[mirror_ubuntu-kernels.git] / fs / proc / base.c

// SPDX-License-Identifier: GPL-2.0
/*
 *  linux/fs/proc/base.c
 *
 *  Copyright (C) 1991, 1992 Linus Torvalds
 *
 *  proc base directory handling functions
 *
 *  1999, Al Viro. Rewritten. Now it covers the whole per-process part.
 *  Instead of using magical inumbers to determine the kind of object
 *  we allocate and fill in-core inodes upon lookup. They don't even
 *  go into icache. We cache the reference to task_struct upon lookup too.
 *  Eventually it should become a filesystem in its own. We don't use the
 *  rest of procfs anymore.
 *
 *
 *  Changelog:
 *  17-Jan-2005
 *  Allan Bezerra
 *  Bruna Moreira <bruna.moreira@indt.org.br>
 *  Edjard Mota <edjard.mota@indt.org.br>
 *  Ilias Biris <ilias.biris@indt.org.br>
 *  Mauricio Lin <mauricio.lin@indt.org.br>
 *
 *  Embedded Linux Lab - 10LE Instituto Nokia de Tecnologia - INdT
 *
 *  A new process specific entry (smaps) included in /proc. It shows the
 *  size of rss for each memory area. The maps entry lacks information
 *  about physical memory size (rss) for each mapped file, i.e.,
 *  rss information for executables and library files.
 *  This additional information is useful for any tools that need to know
 *  about physical memory consumption for a process specific library.
 *
 *  Changelog:
 *  21-Feb-2005
 *  Embedded Linux Lab - 10LE Instituto Nokia de Tecnologia - INdT
 *  Pud inclusion in the page table walking.
 *
 *  ChangeLog:
 *  10-Mar-2005
 *  10LE Instituto Nokia de Tecnologia - INdT:
 *  A better way to walks through the page table as suggested by Hugh Dickins.
 *
 *  Simo Piiroinen <simo.piiroinen@nokia.com>:
 *  Smaps information related to shared, private, clean and dirty pages.
 *
 *  Paul Mundt <paul.mundt@nokia.com>:
 *  Overall revision about smaps.
 */

#include <linux/uaccess.h>

#include <linux/errno.h>
#include <linux/time.h>
#include <linux/proc_fs.h>
#include <linux/stat.h>
#include <linux/task_io_accounting_ops.h>
#include <linux/init.h>
#include <linux/capability.h>
#include <linux/file.h>
#include <linux/fdtable.h>
#include <linux/generic-radix-tree.h>
#include <linux/string.h>
#include <linux/seq_file.h>
#include <linux/namei.h>
#include <linux/mnt_namespace.h>
#include <linux/mm.h>
#include <linux/swap.h>
#include <linux/rcupdate.h>
#include <linux/kallsyms.h>
#include <linux/stacktrace.h>
#include <linux/resource.h>
#include <linux/module.h>
#include <linux/mount.h>
#include <linux/security.h>
#include <linux/ptrace.h>
#include <linux/tracehook.h>
#include <linux/printk.h>
#include <linux/cache.h>
#include <linux/cgroup.h>
#include <linux/cpuset.h>
#include <linux/audit.h>
#include <linux/poll.h>
#include <linux/nsproxy.h>
#include <linux/oom.h>
#include <linux/elf.h>
#include <linux/pid_namespace.h>
#include <linux/user_namespace.h>
#include <linux/fs_struct.h>
#include <linux/slab.h>
#include <linux/sched/autogroup.h>
#include <linux/sched/mm.h>
#include <linux/sched/coredump.h>
#include <linux/sched/debug.h>
#include <linux/sched/stat.h>
#include <linux/posix-timers.h>
#include <linux/time_namespace.h>
#include <linux/resctrl.h>
#include <trace/events/oom.h>
#include "internal.h"
#include "fd.h"

#include "../../lib/kstrtox.h"

/* NOTE:
 *      Implementing inode permission operations in /proc is almost
 *      certainly an error.  Permission checks need to happen during
 *      each system call not at open time.  The reason is that most of
 *      what we wish to check for permissions in /proc varies at runtime.
 *
 *      The classic example of a problem is opening file descriptors
 *      in /proc for a task before it execs a suid executable.
 */

static u8 nlink_tid __ro_after_init;
static u8 nlink_tgid __ro_after_init;

struct pid_entry {
        const char *name;
        unsigned int len;
        umode_t mode;
        const struct inode_operations *iop;
        const struct file_operations *fop;
        union proc_op op;
};

#define NOD(NAME, MODE, IOP, FOP, OP) {                 \
        .name = (NAME),                                 \
        .len  = sizeof(NAME) - 1,                       \
        .mode = MODE,                                   \
        .iop  = IOP,                                    \
        .fop  = FOP,                                    \
        .op   = OP,                                     \
}

#define DIR(NAME, MODE, iops, fops)     \
        NOD(NAME, (S_IFDIR|(MODE)), &iops, &fops, {} )
#define LNK(NAME, get_link)                                     \
        NOD(NAME, (S_IFLNK|S_IRWXUGO),                          \
                &proc_pid_link_inode_operations, NULL,          \
                { .proc_get_link = get_link } )
#define REG(NAME, MODE, fops)                           \
        NOD(NAME, (S_IFREG|(MODE)), NULL, &fops, {})
#define ONE(NAME, MODE, show)                           \
        NOD(NAME, (S_IFREG|(MODE)),                     \
                NULL, &proc_single_file_operations,     \
                { .proc_show = show } )
#define ATTR(LSM, NAME, MODE)                           \
        NOD(NAME, (S_IFREG|(MODE)),                     \
                NULL, &proc_pid_attr_operations,        \
                { .lsm = LSM })

/*
 * Count the number of hardlinks for the pid_entry table, excluding the .
 * and .. links.
 */
static unsigned int __init pid_entry_nlink(const struct pid_entry *entries,
        unsigned int n)
{
        unsigned int i;
        unsigned int count;

        count = 2;
        for (i = 0; i < n; ++i) {
                if (S_ISDIR(entries[i].mode))
                        ++count;
        }

        return count;
}

static int get_task_root(struct task_struct *task, struct path *root)
{
        int result = -ENOENT;

        task_lock(task);
        if (task->fs) {
                get_fs_root(task->fs, root);
                result = 0;
        }
        task_unlock(task);
        return result;
}

static int proc_cwd_link(struct dentry *dentry, struct path *path)
{
        struct task_struct *task = get_proc_task(d_inode(dentry));
        int result = -ENOENT;

        if (task) {
                task_lock(task);
                if (task->fs) {
                        get_fs_pwd(task->fs, path);
                        result = 0;
                }
                task_unlock(task);
                put_task_struct(task);
        }
        return result;
}

static int proc_root_link(struct dentry *dentry, struct path *path)
{
        struct task_struct *task = get_proc_task(d_inode(dentry));
        int result = -ENOENT;

        if (task) {
                result = get_task_root(task, path);
                put_task_struct(task);
        }
        return result;
}

/*
 * If the user used setproctitle(), we just get the string from
 * user space at arg_start, and limit it to a maximum of one page.
 */
static ssize_t get_mm_proctitle(struct mm_struct *mm, char __user *buf,
                                size_t count, unsigned long pos,
                                unsigned long arg_start)
{
        char *page;
        int ret, got;

        if (pos >= PAGE_SIZE)
                return 0;

        page = (char *)__get_free_page(GFP_KERNEL);
        if (!page)
                return -ENOMEM;

        ret = 0;
        got = access_remote_vm(mm, arg_start, page, PAGE_SIZE, FOLL_ANON);
        if (got > 0) {
                int len = strnlen(page, got);

                /* Include the NUL character if it was found */
                if (len < got)
                        len++;

                if (len > pos) {
                        len -= pos;
                        if (len > count)
                                len = count;
                        len -= copy_to_user(buf, page+pos, len);
                        if (!len)
                                len = -EFAULT;
                        ret = len;
                }
        }
        free_page((unsigned long)page);
        return ret;
}

static ssize_t get_mm_cmdline(struct mm_struct *mm, char __user *buf,
                              size_t count, loff_t *ppos)
{
        unsigned long arg_start, arg_end, env_start, env_end;
        unsigned long pos, len;
        char *page, c;

        /* Check if process spawned far enough to have cmdline. */
        if (!mm->env_end)
                return 0;

        spin_lock(&mm->arg_lock);
        arg_start = mm->arg_start;
        arg_end = mm->arg_end;
        env_start = mm->env_start;
        env_end = mm->env_end;
        spin_unlock(&mm->arg_lock);

        if (arg_start >= arg_end)
                return 0;

        /*
         * We allow setproctitle() to overwrite the argument
         * strings, and overflow past the original end. But
         * only when it overflows into the environment area.
         */
        if (env_start != arg_end || env_end < env_start)
                env_start = env_end = arg_end;
        len = env_end - arg_start;

        /* We're not going to care if "*ppos" has high bits set */
        pos = *ppos;
        if (pos >= len)
                return 0;
        if (count > len - pos)
                count = len - pos;
        if (!count)
                return 0;

        /*
         * Magical special case: if the argv[] end byte is not
         * zero, the user has overwritten it with setproctitle(3).
         *
         * Possible future enhancement: do this only once when
         * pos is 0, and set a flag in the 'struct file'.
         */
        if (access_remote_vm(mm, arg_end-1, &c, 1, FOLL_ANON) == 1 && c)
                return get_mm_proctitle(mm, buf, count, pos, arg_start);

        /*
         * For the non-setproctitle() case we limit things strictly
         * to the [arg_start, arg_end[ range.
         */
        pos += arg_start;
        if (pos < arg_start || pos >= arg_end)
                return 0;
        if (count > arg_end - pos)
                count = arg_end - pos;

        page = (char *)__get_free_page(GFP_KERNEL);
        if (!page)
                return -ENOMEM;

        len = 0;
        while (count) {
                int got;
                size_t size = min_t(size_t, PAGE_SIZE, count);

                got = access_remote_vm(mm, pos, page, size, FOLL_ANON);
                if (got <= 0)
                        break;
                got -= copy_to_user(buf, page, got);
                if (unlikely(!got)) {
                        if (!len)
                                len = -EFAULT;
                        break;
                }
                pos += got;
                buf += got;
                len += got;
                count -= got;
        }

        free_page((unsigned long)page);
        return len;
}

static ssize_t get_task_cmdline(struct task_struct *tsk, char __user *buf,
                                size_t count, loff_t *pos)
{
        struct mm_struct *mm;
        ssize_t ret;

        mm = get_task_mm(tsk);
        if (!mm)
                return 0;

        ret = get_mm_cmdline(mm, buf, count, pos);
        mmput(mm);
        return ret;
}

static ssize_t proc_pid_cmdline_read(struct file *file, char __user *buf,
                                     size_t count, loff_t *pos)
{
        struct task_struct *tsk;
        ssize_t ret;

        BUG_ON(*pos < 0);

        tsk = get_proc_task(file_inode(file));
        if (!tsk)
                return -ESRCH;
        ret = get_task_cmdline(tsk, buf, count, pos);
        put_task_struct(tsk);
        if (ret > 0)
                *pos += ret;
        return ret;
}

static const struct file_operations proc_pid_cmdline_ops = {
        .read   = proc_pid_cmdline_read,
        .llseek = generic_file_llseek,
};

#ifdef CONFIG_KALLSYMS
/*
 * Provides a wchan file via kallsyms in a proper one-value-per-file format.
 * Returns the resolved symbol.  If that fails, simply return the address.
 */
static int proc_pid_wchan(struct seq_file *m, struct pid_namespace *ns,
                          struct pid *pid, struct task_struct *task)
{
        unsigned long wchan;
        char symname[KSYM_NAME_LEN];

        if (!ptrace_may_access(task, PTRACE_MODE_READ_FSCREDS))
                goto print0;

        wchan = get_wchan(task);
        if (wchan && !lookup_symbol_name(wchan, symname)) {
                seq_puts(m, symname);
                return 0;
        }

print0:
        seq_putc(m, '0');
        return 0;
}
#endif /* CONFIG_KALLSYMS */

static int lock_trace(struct task_struct *task)
{
        int err = mutex_lock_killable(&task->signal->exec_update_mutex);
        if (err)
                return err;
        if (!ptrace_may_access(task, PTRACE_MODE_ATTACH_FSCREDS)) {
                mutex_unlock(&task->signal->exec_update_mutex);
                return -EPERM;
        }
        return 0;
}

static void unlock_trace(struct task_struct *task)
{
        mutex_unlock(&task->signal->exec_update_mutex);
}

#ifdef CONFIG_STACKTRACE

#define MAX_STACK_TRACE_DEPTH   64

static int proc_pid_stack(struct seq_file *m, struct pid_namespace *ns,
                          struct pid *pid, struct task_struct *task)
{
        unsigned long *entries;
        int err;

        /*
         * The ability to racily run the kernel stack unwinder on a running task
         * and then observe the unwinder output is scary; while it is useful for
         * debugging kernel issues, it can also allow an attacker to leak kernel
         * stack contents.
         * Doing this in a manner that is at least safe from races would require
         * some work to ensure that the remote task can not be scheduled; and
         * even then, this would still expose the unwinder as local attack
         * surface.
         * Therefore, this interface is restricted to root.
         */
        if (!file_ns_capable(m->file, &init_user_ns, CAP_SYS_ADMIN))
                return -EACCES;

        entries = kmalloc_array(MAX_STACK_TRACE_DEPTH, sizeof(*entries),
                                GFP_KERNEL);
        if (!entries)
                return -ENOMEM;

        err = lock_trace(task);
        if (!err) {
                unsigned int i, nr_entries;

                nr_entries = stack_trace_save_tsk(task, entries,
                                                  MAX_STACK_TRACE_DEPTH, 0);

                for (i = 0; i < nr_entries; i++) {
                        seq_printf(m, "[<0>] %pB\n", (void *)entries[i]);
                }

                unlock_trace(task);
        }
        kfree(entries);

        return err;
}
#endif

#ifdef CONFIG_SCHED_INFO
/*
 * Provides /proc/PID/schedstat
 */
static int proc_pid_schedstat(struct seq_file *m, struct pid_namespace *ns,
                              struct pid *pid, struct task_struct *task)
{
        if (unlikely(!sched_info_on()))
                seq_puts(m, "0 0 0\n");
        else
                seq_printf(m, "%llu %llu %lu\n",
                   (unsigned long long)task->se.sum_exec_runtime,
                   (unsigned long long)task->sched_info.run_delay,
                   task->sched_info.pcount);

        return 0;
}
#endif

#ifdef CONFIG_LATENCYTOP
static int lstats_show_proc(struct seq_file *m, void *v)
{
        int i;
        struct inode *inode = m->private;
        struct task_struct *task = get_proc_task(inode);

        if (!task)
                return -ESRCH;
        seq_puts(m, "Latency Top version : v0.1\n");
        for (i = 0; i < LT_SAVECOUNT; i++) {
                struct latency_record *lr = &task->latency_record[i];
                if (lr->backtrace[0]) {
                        int q;
                        seq_printf(m, "%i %li %li",
                                   lr->count, lr->time, lr->max);
                        for (q = 0; q < LT_BACKTRACEDEPTH; q++) {
                                unsigned long bt = lr->backtrace[q];

                                if (!bt)
                                        break;
                                seq_printf(m, " %ps", (void *)bt);
                        }
                        seq_putc(m, '\n');
                }

        }
        put_task_struct(task);
        return 0;
}

static int lstats_open(struct inode *inode, struct file *file)
{
        return single_open(file, lstats_show_proc, inode);
}

static ssize_t lstats_write(struct file *file, const char __user *buf,
                            size_t count, loff_t *offs)
{
        struct task_struct *task = get_proc_task(file_inode(file));

        if (!task)
                return -ESRCH;
        clear_tsk_latency_tracing(task);
        put_task_struct(task);

        return count;
}

static const struct file_operations proc_lstats_operations = {
        .open           = lstats_open,
        .read           = seq_read,
        .write          = lstats_write,
        .llseek         = seq_lseek,
        .release        = single_release,
};

#endif

static int proc_oom_score(struct seq_file *m, struct pid_namespace *ns,
                          struct pid *pid, struct task_struct *task)
{
        unsigned long totalpages = totalram_pages() + total_swap_pages;
        unsigned long points = 0;

        points = oom_badness(task, totalpages) * 1000 / totalpages;
        seq_printf(m, "%lu\n", points);

        return 0;
}

struct limit_names {
        const char *name;
        const char *unit;
};

static const struct limit_names lnames[RLIM_NLIMITS] = {
        [RLIMIT_CPU] = {"Max cpu time", "seconds"},
        [RLIMIT_FSIZE] = {"Max file size", "bytes"},
        [RLIMIT_DATA] = {"Max data size", "bytes"},
        [RLIMIT_STACK] = {"Max stack size", "bytes"},
        [RLIMIT_CORE] = {"Max core file size", "bytes"},
        [RLIMIT_RSS] = {"Max resident set", "bytes"},
        [RLIMIT_NPROC] = {"Max processes", "processes"},
        [RLIMIT_NOFILE] = {"Max open files", "files"},
        [RLIMIT_MEMLOCK] = {"Max locked memory", "bytes"},
        [RLIMIT_AS] = {"Max address space", "bytes"},
        [RLIMIT_LOCKS] = {"Max file locks", "locks"},
        [RLIMIT_SIGPENDING] = {"Max pending signals", "signals"},
        [RLIMIT_MSGQUEUE] = {"Max msgqueue size", "bytes"},
        [RLIMIT_NICE] = {"Max nice priority", NULL},
        [RLIMIT_RTPRIO] = {"Max realtime priority", NULL},
        [RLIMIT_RTTIME] = {"Max realtime timeout", "us"},
};

/* Display limits for a process */
static int proc_pid_limits(struct seq_file *m, struct pid_namespace *ns,
                           struct pid *pid, struct task_struct *task)
{
        unsigned int i;
        unsigned long flags;

        struct rlimit rlim[RLIM_NLIMITS];

        if (!lock_task_sighand(task, &flags))
                return 0;
        memcpy(rlim, task->signal->rlim, sizeof(struct rlimit) * RLIM_NLIMITS);
        unlock_task_sighand(task, &flags);

        /*
         * print the file header
         */
        seq_puts(m, "Limit                     "
                "Soft Limit           "
                "Hard Limit           "
                "Units     \n");

        for (i = 0; i < RLIM_NLIMITS; i++) {
                if (rlim[i].rlim_cur == RLIM_INFINITY)
                        seq_printf(m, "%-25s %-20s ",
                                   lnames[i].name, "unlimited");
                else
                        seq_printf(m, "%-25s %-20lu ",
                                   lnames[i].name, rlim[i].rlim_cur);

                if (rlim[i].rlim_max == RLIM_INFINITY)
                        seq_printf(m, "%-20s ", "unlimited");
                else
                        seq_printf(m, "%-20lu ", rlim[i].rlim_max);

                if (lnames[i].unit)
                        seq_printf(m, "%-10s\n", lnames[i].unit);
                else
                        seq_putc(m, '\n');
        }

        return 0;
}

#ifdef CONFIG_HAVE_ARCH_TRACEHOOK
static int proc_pid_syscall(struct seq_file *m, struct pid_namespace *ns,
                            struct pid *pid, struct task_struct *task)
{
        struct syscall_info info;
        u64 *args = &info.data.args[0];
        int res;

        res = lock_trace(task);
        if (res)
                return res;

        if (task_current_syscall(task, &info))
                seq_puts(m, "running\n");
        else if (info.data.nr < 0)
                seq_printf(m, "%d 0x%llx 0x%llx\n",
                           info.data.nr, info.sp, info.data.instruction_pointer);
        else
                seq_printf(m,
                       "%d 0x%llx 0x%llx 0x%llx 0x%llx 0x%llx 0x%llx 0x%llx 0x%llx\n",
                       info.data.nr,
                       args[0], args[1], args[2], args[3], args[4], args[5],
                       info.sp, info.data.instruction_pointer);
        unlock_trace(task);

        return 0;
}
#endif /* CONFIG_HAVE_ARCH_TRACEHOOK */

/************************************************************************/
/*                       Here the fs part begins                        */
/************************************************************************/

/* permission checks */
static int proc_fd_access_allowed(struct inode *inode)
{
        struct task_struct *task;
        int allowed = 0;
        /* Allow access to a task's file descriptors if it is us or we
         * may use ptrace attach to the process and find out that
         * information.
         */
        task = get_proc_task(inode);
        if (task) {
                allowed = ptrace_may_access(task, PTRACE_MODE_READ_FSCREDS);
                put_task_struct(task);
        }
        return allowed;
}

int proc_setattr(struct dentry *dentry, struct iattr *attr)
{
        int error;
        struct inode *inode = d_inode(dentry);

        if (attr->ia_valid & ATTR_MODE)
                return -EPERM;

        error = setattr_prepare(dentry, attr);
        if (error)
                return error;

        setattr_copy(inode, attr);
        mark_inode_dirty(inode);
        return 0;
}

/*
 * May current process learn task's sched/cmdline info (for hide_pid_min=1)
 * or euid/egid (for hide_pid_min=2)?
 */
static bool has_pid_permissions(struct proc_fs_info *fs_info,
                                 struct task_struct *task,
                                 enum proc_hidepid hide_pid_min)
{
        /*
         * If 'hidpid' mount option is set force a ptrace check,
         * we indicate that we are using a filesystem syscall
         * by passing PTRACE_MODE_READ_FSCREDS
         */
        if (fs_info->hide_pid == HIDEPID_NOT_PTRACEABLE)
                return ptrace_may_access(task, PTRACE_MODE_READ_FSCREDS);

        if (fs_info->hide_pid < hide_pid_min)
                return true;
        if (in_group_p(fs_info->pid_gid))
                return true;
        return ptrace_may_access(task, PTRACE_MODE_READ_FSCREDS);
}


static int proc_pid_permission(struct inode *inode, int mask)
{
        struct proc_fs_info *fs_info = proc_sb_info(inode->i_sb);
        struct task_struct *task;
        bool has_perms;

        task = get_proc_task(inode);
        if (!task)
                return -ESRCH;
        has_perms = has_pid_permissions(fs_info, task, HIDEPID_NO_ACCESS);
        put_task_struct(task);

        if (!has_perms) {
                if (fs_info->hide_pid == HIDEPID_INVISIBLE) {
                        /*
                         * Let's make getdents(), stat(), and open()
                         * consistent with each other.  If a process
                         * may not stat() a file, it shouldn't be seen
                         * in procfs at all.
                         */
                        return -ENOENT;
                }

                return -EPERM;
        }
        return generic_permission(inode, mask);
}



static const struct inode_operations proc_def_inode_operations = {
        .setattr        = proc_setattr,
};

static int proc_single_show(struct seq_file *m, void *v)
{
        struct inode *inode = m->private;
        struct pid_namespace *ns = proc_pid_ns(inode->i_sb);
        struct pid *pid = proc_pid(inode);
        struct task_struct *task;
        int ret;

        task = get_pid_task(pid, PIDTYPE_PID);
        if (!task)
                return -ESRCH;

        ret = PROC_I(inode)->op.proc_show(m, ns, pid, task);

        put_task_struct(task);
        return ret;
}

static int proc_single_open(struct inode *inode, struct file *filp)
{
        return single_open(filp, proc_single_show, inode);
}

static const struct file_operations proc_single_file_operations = {
        .open           = proc_single_open,
        .read           = seq_read,
        .llseek         = seq_lseek,
        .release        = single_release,
};


struct mm_struct *proc_mem_open(struct inode *inode, unsigned int mode)
{
        struct task_struct *task = get_proc_task(inode);
        struct mm_struct *mm = ERR_PTR(-ESRCH);

        if (task) {
                mm = mm_access(task, mode | PTRACE_MODE_FSCREDS);
                put_task_struct(task);

                if (!IS_ERR_OR_NULL(mm)) {
                        /* ensure this mm_struct can't be freed */
                        mmgrab(mm);
                        /* but do not pin its memory */
                        mmput(mm);
                }
        }

        return mm;
}

static int __mem_open(struct inode *inode, struct file *file, unsigned int mode)
{
        struct mm_struct *mm = proc_mem_open(inode, mode);

        if (IS_ERR(mm))
                return PTR_ERR(mm);

        file->private_data = mm;
        return 0;
}

static int mem_open(struct inode *inode, struct file *file)
{
        int ret = __mem_open(inode, file, PTRACE_MODE_ATTACH);

        /* OK to pass negative loff_t, we can catch out-of-range */
        file->f_mode |= FMODE_UNSIGNED_OFFSET;

        return ret;
}

static ssize_t mem_rw(struct file *file, char __user *buf,
                        size_t count, loff_t *ppos, int write)
{
        struct mm_struct *mm = file->private_data;
        unsigned long addr = *ppos;
        ssize_t copied;
        char *page;
        unsigned int flags;

        if (!mm)
                return 0;

        page = (char *)__get_free_page(GFP_KERNEL);
        if (!page)
                return -ENOMEM;

        copied = 0;
        if (!mmget_not_zero(mm))
                goto free;

        flags = FOLL_FORCE | (write ? FOLL_WRITE : 0);

        while (count > 0) {
                int this_len = min_t(int, count, PAGE_SIZE);

                if (write && copy_from_user(page, buf, this_len)) {
                        copied = -EFAULT;
                        break;
                }

                this_len = access_remote_vm(mm, addr, page, this_len, flags);
                if (!this_len) {
                        if (!copied)
                                copied = -EIO;
                        break;
                }

                if (!write && copy_to_user(buf, page, this_len)) {
                        copied = -EFAULT;
                        break;
                }

                buf += this_len;
                addr += this_len;
                copied += this_len;
                count -= this_len;
        }
        *ppos = addr;

        mmput(mm);
free:
        free_page((unsigned long) page);
        return copied;
}

static ssize_t mem_read(struct file *file, char __user *buf,
                        size_t count, loff_t *ppos)
{
        return mem_rw(file, buf, count, ppos, 0);
}

static ssize_t mem_write(struct file *file, const char __user *buf,
                         size_t count, loff_t *ppos)
{
        return mem_rw(file, (char __user*)buf, count, ppos, 1);
}

loff_t mem_lseek(struct file *file, loff_t offset, int orig)
{
        switch (orig) {
        case 0:
                file->f_pos = offset;
                break;
        case 1:
                file->f_pos += offset;
                break;
        default:
                return -EINVAL;
        }
        force_successful_syscall_return();
        return file->f_pos;
}

static int mem_release(struct inode *inode, struct file *file)
{
        struct mm_struct *mm = file->private_data;
        if (mm)
                mmdrop(mm);
        return 0;
}

static const struct file_operations proc_mem_operations = {
        .llseek         = mem_lseek,
        .read           = mem_read,
        .write          = mem_write,
        .open           = mem_open,
        .release        = mem_release,
};

static int environ_open(struct inode *inode, struct file *file)
{
        return __mem_open(inode, file, PTRACE_MODE_READ);
}

static ssize_t environ_read(struct file *file, char __user *buf,
                        size_t count, loff_t *ppos)
{
        char *page;
        unsigned long src = *ppos;
        int ret = 0;
        struct mm_struct *mm = file->private_data;
        unsigned long env_start, env_end;

        /* Ensure the process spawned far enough to have an environment. */
        if (!mm || !mm->env_end)
                return 0;

        page = (char *)__get_free_page(GFP_KERNEL);
        if (!page)
                return -ENOMEM;

        ret = 0;
        if (!mmget_not_zero(mm))
                goto free;

        spin_lock(&mm->arg_lock);
        env_start = mm->env_start;
        env_end = mm->env_end;
        spin_unlock(&mm->arg_lock);

        while (count > 0) {
                size_t this_len, max_len;
                int retval;

                if (src >= (env_end - env_start))
                        break;

                this_len = env_end - (env_start + src);

                max_len = min_t(size_t, PAGE_SIZE, count);
                this_len = min(max_len, this_len);

                retval = access_remote_vm(mm, (env_start + src), page, this_len, FOLL_ANON);

                if (retval <= 0) {
                        ret = retval;
                        break;
                }

                if (copy_to_user(buf, page, retval)) {
                        ret = -EFAULT;
                        break;
                }

                ret += retval;
                src += retval;
                buf += retval;
                count -= retval;
        }
        *ppos = src;
        mmput(mm);

free:
        free_page((unsigned long) page);
        return ret;
}

static const struct file_operations proc_environ_operations = {
        .open           = environ_open,
        .read           = environ_read,
        .llseek         = generic_file_llseek,
        .release        = mem_release,
};

static int auxv_open(struct inode *inode, struct file *file)
{
        return __mem_open(inode, file, PTRACE_MODE_READ_FSCREDS);
}

static ssize_t auxv_read(struct file *file, char __user *buf,
                        size_t count, loff_t *ppos)
{
        struct mm_struct *mm = file->private_data;
        unsigned int nwords = 0;

        if (!mm)
                return 0;
        do {
                nwords += 2;
        } while (mm->saved_auxv[nwords - 2] != 0); /* AT_NULL */
        return simple_read_from_buffer(buf, count, ppos, mm->saved_auxv,
                                       nwords * sizeof(mm->saved_auxv[0]));
}

static const struct file_operations proc_auxv_operations = {
        .open           = auxv_open,
        .read           = auxv_read,
        .llseek         = generic_file_llseek,
        .release        = mem_release,
};

static ssize_t oom_adj_read(struct file *file, char __user *buf, size_t count,
                            loff_t *ppos)
{
        struct task_struct *task = get_proc_task(file_inode(file));
        char buffer[PROC_NUMBUF];
        int oom_adj = OOM_ADJUST_MIN;
        size_t len;

        if (!task)
                return -ESRCH;
        if (task->signal->oom_score_adj == OOM_SCORE_ADJ_MAX)
                oom_adj = OOM_ADJUST_MAX;
        else
                oom_adj = (task->signal->oom_score_adj * -OOM_DISABLE) /
                          OOM_SCORE_ADJ_MAX;
        put_task_struct(task);
        len = snprintf(buffer, sizeof(buffer), "%d\n", oom_adj);
        return simple_read_from_buffer(buf, count, ppos, buffer, len);
}

static int __set_oom_adj(struct file *file, int oom_adj, bool legacy)
{
        static DEFINE_MUTEX(oom_adj_mutex);
        struct mm_struct *mm = NULL;
        struct task_struct *task;
        int err = 0;

        task = get_proc_task(file_inode(file));
        if (!task)
                return -ESRCH;

        mutex_lock(&oom_adj_mutex);
        if (legacy) {
                if (oom_adj < task->signal->oom_score_adj &&
                                !capable(CAP_SYS_RESOURCE)) {
                        err = -EACCES;
                        goto err_unlock;
                }
                /*
                 * /proc/pid/oom_adj is provided for legacy purposes, ask users to use
                 * /proc/pid/oom_score_adj instead.
                 */
                pr_warn_once("%s (%d): /proc/%d/oom_adj is deprecated, please use /proc/%d/oom_score_adj instead.\n",
                          current->comm, task_pid_nr(current), task_pid_nr(task),
                          task_pid_nr(task));
        } else {
                if ((short)oom_adj < task->signal->oom_score_adj_min &&
                                !capable(CAP_SYS_RESOURCE)) {
                        err = -EACCES;
                        goto err_unlock;
                }
        }

        /*
         * Make sure we will check other processes sharing the mm if this is
         * not vfrok which wants its own oom_score_adj.
         * pin the mm so it doesn't go away and get reused after task_unlock
         */
        if (!task->vfork_done) {
                struct task_struct *p = find_lock_task_mm(task);

                if (p) {
                        if (atomic_read(&p->mm->mm_users) > 1) {
                                mm = p->mm;
                                mmgrab(mm);
                        }
                        task_unlock(p);
                }
        }

        task->signal->oom_score_adj = oom_adj;
        if (!legacy && has_capability_noaudit(current, CAP_SYS_RESOURCE))
                task->signal->oom_score_adj_min = (short)oom_adj;
        trace_oom_score_adj_update(task);

        if (mm) {
                struct task_struct *p;

                rcu_read_lock();
                for_each_process(p) {
                        if (same_thread_group(task, p))
                                continue;

                        /* do not touch kernel threads or the global init */
                        if (p->flags & PF_KTHREAD || is_global_init(p))
                                continue;

                        task_lock(p);
                        if (!p->vfork_done && process_shares_mm(p, mm)) {
                                p->signal->oom_score_adj = oom_adj;
                                if (!legacy && has_capability_noaudit(current, CAP_SYS_RESOURCE))
                                        p->signal->oom_score_adj_min = (short)oom_adj;
                        }
                        task_unlock(p);
                }
                rcu_read_unlock();
                mmdrop(mm);
        }
err_unlock:
        mutex_unlock(&oom_adj_mutex);
        put_task_struct(task);
        return err;
}

/*
 * /proc/pid/oom_adj exists solely for backwards compatibility with previous
 * kernels.  The effective policy is defined by oom_score_adj, which has a
 * different scale: oom_adj grew exponentially and oom_score_adj grows linearly.
 * Values written to oom_adj are simply mapped linearly to oom_score_adj.
 * Processes that become oom disabled via oom_adj will still be oom disabled
 * with this implementation.
 *
 * oom_adj cannot be removed since existing userspace binaries use it.
 */
static ssize_t oom_adj_write(struct file *file, const char __user *buf,
                             size_t count, loff_t *ppos)
{
        char buffer[PROC_NUMBUF];
        int oom_adj;
        int err;

        memset(buffer, 0, sizeof(buffer));
        if (count > sizeof(buffer) - 1)
                count = sizeof(buffer) - 1;
        if (copy_from_user(buffer, buf, count)) {
                err = -EFAULT;
                goto out;
        }

        err = kstrtoint(strstrip(buffer), 0, &oom_adj);
        if (err)
                goto out;
        if ((oom_adj < OOM_ADJUST_MIN || oom_adj > OOM_ADJUST_MAX) &&
             oom_adj != OOM_DISABLE) {
                err = -EINVAL;
                goto out;
        }

        /*
         * Scale /proc/pid/oom_score_adj appropriately ensuring that a maximum
         * value is always attainable.
         */
        if (oom_adj == OOM_ADJUST_MAX)
                oom_adj = OOM_SCORE_ADJ_MAX;
        else
                oom_adj = (oom_adj * OOM_SCORE_ADJ_MAX) / -OOM_DISABLE;

        err = __set_oom_adj(file, oom_adj, true);
out:
        return err < 0 ? err : count;
}

static const struct file_operations proc_oom_adj_operations = {
        .read           = oom_adj_read,
        .write          = oom_adj_write,
        .llseek         = generic_file_llseek,
};

static ssize_t oom_score_adj_read(struct file *file, char __user *buf,
                                        size_t count, loff_t *ppos)
{
        struct task_struct *task = get_proc_task(file_inode(file));
        char buffer[PROC_NUMBUF];
        short oom_score_adj = OOM_SCORE_ADJ_MIN;
        size_t len;

        if (!task)
                return -ESRCH;
        oom_score_adj = task->signal->oom_score_adj;
        put_task_struct(task);
        len = snprintf(buffer, sizeof(buffer), "%hd\n", oom_score_adj);
        return simple_read_from_buffer(buf, count, ppos, buffer, len);
}

static ssize_t oom_score_adj_write(struct file *file, const char __user *buf,
                                        size_t count, loff_t *ppos)
{
        char buffer[PROC_NUMBUF];
        int oom_score_adj;
        int err;

        memset(buffer, 0, sizeof(buffer));
        if (count > sizeof(buffer) - 1)
                count = sizeof(buffer) - 1;
        if (copy_from_user(buffer, buf, count)) {
                err = -EFAULT;
                goto out;
        }

        err = kstrtoint(strstrip(buffer), 0, &oom_score_adj);
        if (err)
                goto out;
        if (oom_score_adj < OOM_SCORE_ADJ_MIN ||
                        oom_score_adj > OOM_SCORE_ADJ_MAX) {
                err = -EINVAL;
                goto out;
        }

        err = __set_oom_adj(file, oom_score_adj, false);
out:
        return err < 0 ? err : count;
}

static const struct file_operations proc_oom_score_adj_operations = {
        .read           = oom_score_adj_read,
        .write          = oom_score_adj_write,
        .llseek         = default_llseek,
};

#ifdef CONFIG_AUDIT
#define TMPBUFLEN 11
static ssize_t proc_loginuid_read(struct file * file, char __user * buf,
                                  size_t count, loff_t *ppos)
{
        struct inode * inode = file_inode(file);
        struct task_struct *task = get_proc_task(inode);
        ssize_t length;
        char tmpbuf[TMPBUFLEN];

        if (!task)
                return -ESRCH;
        length = scnprintf(tmpbuf, TMPBUFLEN, "%u",
                           from_kuid(file->f_cred->user_ns,
                                     audit_get_loginuid(task)));
        put_task_struct(task);
        return simple_read_from_buffer(buf, count, ppos, tmpbuf, length);
}

static ssize_t proc_loginuid_write(struct file * file, const char __user * buf,
                                   size_t count, loff_t *ppos)
{
        struct inode * inode = file_inode(file);
        uid_t loginuid;
        kuid_t kloginuid;
        int rv;

        rcu_read_lock();
        if (current != pid_task(proc_pid(inode), PIDTYPE_PID)) {
                rcu_read_unlock();
                return -EPERM;
        }
        rcu_read_unlock();

        if (*ppos != 0) {
                /* No partial writes. */
                return -EINVAL;
        }

        rv = kstrtou32_from_user(buf, count, 10, &loginuid);
        if (rv < 0)
                return rv;

        /* is userspace tring to explicitly UNSET the loginuid? */
        if (loginuid == AUDIT_UID_UNSET) {
                kloginuid = INVALID_UID;
        } else {
                kloginuid = make_kuid(file->f_cred->user_ns, loginuid);
                if (!uid_valid(kloginuid))
                        return -EINVAL;
        }

        rv = audit_set_loginuid(kloginuid);
        if (rv < 0)
                return rv;
        return count;
}

static const struct file_operations proc_loginuid_operations = {
        .read           = proc_loginuid_read,
        .write          = proc_loginuid_write,
        .llseek         = generic_file_llseek,
};

static ssize_t proc_sessionid_read(struct file * file, char __user * buf,
                                  size_t count, loff_t *ppos)
{
        struct inode * inode = file_inode(file);
        struct task_struct *task = get_proc_task(inode);
        ssize_t length;
        char tmpbuf[TMPBUFLEN];

        if (!task)
                return -ESRCH;
        length = scnprintf(tmpbuf, TMPBUFLEN, "%u",
                                audit_get_sessionid(task));
        put_task_struct(task);
        return simple_read_from_buffer(buf, count, ppos, tmpbuf, length);
}

static const struct file_operations proc_sessionid_operations = {
        .read           = proc_sessionid_read,
        .llseek         = generic_file_llseek,
};
#endif

#ifdef CONFIG_FAULT_INJECTION
static ssize_t proc_fault_inject_read(struct file * file, char __user * buf,
                                      size_t count, loff_t *ppos)
{
        struct task_struct *task = get_proc_task(file_inode(file));
        char buffer[PROC_NUMBUF];
        size_t len;
        int make_it_fail;

        if (!task)
                return -ESRCH;
        make_it_fail = task->make_it_fail;
        put_task_struct(task);

        len = snprintf(buffer, sizeof(buffer), "%i\n", make_it_fail);

        return simple_read_from_buffer(buf, count, ppos, buffer, len);
}

static ssize_t proc_fault_inject_write(struct file * file,
                        const char __user * buf, size_t count, loff_t *ppos)
{
        struct task_struct *task;
        char buffer[PROC_NUMBUF];
        int make_it_fail;
        int rv;

        if (!capable(CAP_SYS_RESOURCE))
                return -EPERM;
        memset(buffer, 0, sizeof(buffer));
        if (count > sizeof(buffer) - 1)
                count = sizeof(buffer) - 1;
        if (copy_from_user(buffer, buf, count))
                return -EFAULT;
        rv = kstrtoint(strstrip(buffer), 0, &make_it_fail);
        if (rv < 0)
                return rv;
        if (make_it_fail < 0 || make_it_fail > 1)
                return -EINVAL;

        task = get_proc_task(file_inode(file));
        if (!task)
                return -ESRCH;
        task->make_it_fail = make_it_fail;
        put_task_struct(task);

        return count;
}

static const struct file_operations proc_fault_inject_operations = {
        .read           = proc_fault_inject_read,
        .write          = proc_fault_inject_write,
        .llseek         = generic_file_llseek,
};

static ssize_t proc_fail_nth_write(struct file *file, const char __user *buf,
                                   size_t count, loff_t *ppos)
{
        struct task_struct *task;
        int err;
        unsigned int n;

        err = kstrtouint_from_user(buf, count, 0, &n);
        if (err)
                return err;

        task = get_proc_task(file_inode(file));
        if (!task)
                return -ESRCH;
        task->fail_nth = n;
        put_task_struct(task);

        return count;
}

static ssize_t proc_fail_nth_read(struct file *file, char __user *buf,
                                  size_t count, loff_t *ppos)
{
        struct task_struct *task;
        char numbuf[PROC_NUMBUF];
        ssize_t len;

        task = get_proc_task(file_inode(file));
        if (!task)
                return -ESRCH;
        len = snprintf(numbuf, sizeof(numbuf), "%u\n", task->fail_nth);
        put_task_struct(task);
        return simple_read_from_buffer(buf, count, ppos, numbuf, len);
}

static const struct file_operations proc_fail_nth_operations = {
        .read           = proc_fail_nth_read,
        .write          = proc_fail_nth_write,
};
#endif


#ifdef CONFIG_SCHED_DEBUG
/*
 * Print out various scheduling related per-task fields:
 */
static int sched_show(struct seq_file *m, void *v)
{
        struct inode *inode = m->private;
        struct pid_namespace *ns = proc_pid_ns(inode->i_sb);
        struct task_struct *p;

        p = get_proc_task(inode);
        if (!p)
                return -ESRCH;
        proc_sched_show_task(p, ns, m);

        put_task_struct(p);

        return 0;
}

static ssize_t
sched_write(struct file *file, const char __user *buf,
            size_t count, loff_t *offset)
{
        struct inode *inode = file_inode(file);
        struct task_struct *p;

        p = get_proc_task(inode);
        if (!p)
                return -ESRCH;
        proc_sched_set_task(p);

        put_task_struct(p);

        return count;
}

static int sched_open(struct inode *inode, struct file *filp)
{
        return single_open(filp, sched_show, inode);
}

static const struct file_operations proc_pid_sched_operations = {
        .open           = sched_open,
        .read           = seq_read,
        .write          = sched_write,
        .llseek         = seq_lseek,
        .release        = single_release,
};

#endif

#ifdef CONFIG_SCHED_AUTOGROUP
/*
 * Print out autogroup related information:
 */
static int sched_autogroup_show(struct seq_file *m, void *v)
{
        struct inode *inode = m->private;
        struct task_struct *p;

        p = get_proc_task(inode);
        if (!p)
                return -ESRCH;
        proc_sched_autogroup_show_task(p, m);

        put_task_struct(p);

        return 0;
}

static ssize_t
sched_autogroup_write(struct file *file, const char __user *buf,
            size_t count, loff_t *offset)
{
        struct inode *inode = file_inode(file);
        struct task_struct *p;
        char buffer[PROC_NUMBUF];
        int nice;
        int err;

        memset(buffer, 0, sizeof(buffer));
        if (count > sizeof(buffer) - 1)
                count = sizeof(buffer) - 1;
        if (copy_from_user(buffer, buf, count))
                return -EFAULT;

        err = kstrtoint(strstrip(buffer), 0, &nice);
        if (err < 0)
                return err;

        p = get_proc_task(inode);
        if (!p)
                return -ESRCH;

        err = proc_sched_autogroup_set_nice(p, nice);
        if (err)
                count = err;

        put_task_struct(p);

        return count;
}

static int sched_autogroup_open(struct inode *inode, struct file *filp)
{
        int ret;

        ret = single_open(filp, sched_autogroup_show, NULL);
        if (!ret) {
                struct seq_file *m = filp->private_data;

                m->private = inode;
        }
        return ret;
}

static const struct file_operations proc_pid_sched_autogroup_operations = {
        .open           = sched_autogroup_open,
        .read           = seq_read,
        .write          = sched_autogroup_write,
        .llseek         = seq_lseek,
        .release        = single_release,
};

#endif /* CONFIG_SCHED_AUTOGROUP */

#ifdef CONFIG_TIME_NS
static int timens_offsets_show(struct seq_file *m, void *v)
{
        struct task_struct *p;

        p = get_proc_task(file_inode(m->file));
        if (!p)
                return -ESRCH;
        proc_timens_show_offsets(p, m);

        put_task_struct(p);

        return 0;
}

static ssize_t timens_offsets_write(struct file *file, const char __user *buf,
                                    size_t count, loff_t *ppos)
{
        struct inode *inode = file_inode(file);
        struct proc_timens_offset offsets[2];
        char *kbuf = NULL, *pos, *next_line;
        struct task_struct *p;
        int ret, noffsets;

        /* Only allow < page size writes at the beginning of the file */
        if ((*ppos != 0) || (count >= PAGE_SIZE))
                return -EINVAL;

        /* Slurp in the user data */
        kbuf = memdup_user_nul(buf, count);
        if (IS_ERR(kbuf))
                return PTR_ERR(kbuf);

        /* Parse the user data */
        ret = -EINVAL;
        noffsets = 0;
        for (pos = kbuf; pos; pos = next_line) {
                struct proc_timens_offset *off = &offsets[noffsets];
                char clock[10];
                int err;

                /* Find the end of line and ensure we don't look past it */
                next_line = strchr(pos, '\n');
                if (next_line) {
                        *next_line = '\0';
                        next_line++;
                        if (*next_line == '\0')
                                next_line = NULL;
                }

                err = sscanf(pos, "%9s %lld %lu", clock,
                                &off->val.tv_sec, &off->val.tv_nsec);
                if (err != 3 || off->val.tv_nsec >= NSEC_PER_SEC)
                        goto out;

                clock[sizeof(clock) - 1] = 0;
                if (strcmp(clock, "monotonic") == 0 ||
                    strcmp(clock, __stringify(CLOCK_MONOTONIC)) == 0)
                        off->clockid = CLOCK_MONOTONIC;
                else if (strcmp(clock, "boottime") == 0 ||
                         strcmp(clock, __stringify(CLOCK_BOOTTIME)) == 0)
                        off->clockid = CLOCK_BOOTTIME;
                else
                        goto out;

                noffsets++;
                if (noffsets == ARRAY_SIZE(offsets)) {
                        if (next_line)
                                count = next_line - kbuf;
                        break;
                }
        }

        ret = -ESRCH;
        p = get_proc_task(inode);
        if (!p)
                goto out;
        ret = proc_timens_set_offset(file, p, offsets, noffsets);
        put_task_struct(p);
        if (ret)
                goto out;

        ret = count;
out:
        kfree(kbuf);
        return ret;
}

static int timens_offsets_open(struct inode *inode, struct file *filp)
{
        return single_open(filp, timens_offsets_show, inode);
}

static const struct file_operations proc_timens_offsets_operations = {
        .open           = timens_offsets_open,
        .read           = seq_read,
        .write          = timens_offsets_write,
        .llseek         = seq_lseek,
        .release        = single_release,
};
#endif /* CONFIG_TIME_NS */

static ssize_t comm_write(struct file *file, const char __user *buf,
                                size_t count, loff_t *offset)
{
        struct inode *inode = file_inode(file);
        struct task_struct *p;
        char buffer[TASK_COMM_LEN];
        const size_t maxlen = sizeof(buffer) - 1;

        memset(buffer, 0, sizeof(buffer));
        if (copy_from_user(buffer, buf, count > maxlen ? maxlen : count))
                return -EFAULT;

        p = get_proc_task(inode);
        if (!p)
                return -ESRCH;

        if (same_thread_group(current, p))
                set_task_comm(p, buffer);
        else
                count = -EINVAL;

        put_task_struct(p);

        return count;
}

static int comm_show(struct seq_file *m, void *v)
{
        struct inode *inode = m->private;
        struct task_struct *p;

        p = get_proc_task(inode);
        if (!p)
                return -ESRCH;

        proc_task_name(m, p, false);
        seq_putc(m, '\n');

        put_task_struct(p);

        return 0;
}

static int comm_open(struct inode *inode, struct file *filp)
{
        return single_open(filp, comm_show, inode);
}

static const struct file_operations proc_pid_set_comm_operations = {
        .open           = comm_open,
        .read           = seq_read,
        .write          = comm_write,
        .llseek         = seq_lseek,
        .release        = single_release,
};

static int proc_exe_link(struct dentry *dentry, struct path *exe_path)
{
        struct task_struct *task;
        struct file *exe_file;

        task = get_proc_task(d_inode(dentry));
        if (!task)
                return -ENOENT;
        exe_file = get_task_exe_file(task);
        put_task_struct(task);
        if (exe_file) {
                *exe_path = exe_file->f_path;
                path_get(&exe_file->f_path);
                fput(exe_file);
                return 0;
        } else
                return -ENOENT;
}

static const char *proc_pid_get_link(struct dentry *dentry,
                                     struct inode *inode,
                                     struct delayed_call *done)
{
        struct path path;
        int error = -EACCES;

        if (!dentry)
                return ERR_PTR(-ECHILD);

        /* Are we allowed to snoop on the tasks file descriptors? */
        if (!proc_fd_access_allowed(inode))
                goto out;

        error = PROC_I(inode)->op.proc_get_link(dentry, &path);
        if (error)
                goto out;

        error = nd_jump_link(&path);
out:
        return ERR_PTR(error);
}

static int do_proc_readlink(struct path *path, char __user *buffer, int buflen)
{
        char *tmp = (char *)__get_free_page(GFP_KERNEL);
        char *pathname;
        int len;

        if (!tmp)
                return -ENOMEM;

        pathname = d_path(path, tmp, PAGE_SIZE);
        len = PTR_ERR(pathname);
        if (IS_ERR(pathname))
                goto out;
        len = tmp + PAGE_SIZE - 1 - pathname;

        if (len > buflen)
                len = buflen;
        if (copy_to_user(buffer, pathname, len))
                len = -EFAULT;
 out:
        free_page((unsigned long)tmp);
        return len;
}

static int proc_pid_readlink(struct dentry * dentry, char __user * buffer, int buflen)
{
        int error = -EACCES;
        struct inode *inode = d_inode(dentry);
        struct path path;

        /* Are we allowed to snoop on the tasks file descriptors? */
        if (!proc_fd_access_allowed(inode))
                goto out;

        error = PROC_I(inode)->op.proc_get_link(dentry, &path);
        if (error)
                goto out;

        error = do_proc_readlink(&path, buffer, buflen);
        path_put(&path);
out:
        return error;
}

const struct inode_operations proc_pid_link_inode_operations = {
        .readlink       = proc_pid_readlink,
        .get_link       = proc_pid_get_link,
        .setattr        = proc_setattr,
};


/* building an inode */

void task_dump_owner(struct task_struct *task, umode_t mode,
                     kuid_t *ruid, kgid_t *rgid)
{
        /* Depending on the state of dumpable compute who should own a
         * proc file for a task.
         */
        const struct cred *cred;
        kuid_t uid;
        kgid_t gid;

        if (unlikely(task->flags & PF_KTHREAD)) {
                *ruid = GLOBAL_ROOT_UID;
                *rgid = GLOBAL_ROOT_GID;
                return;
        }

        /* Default to the tasks effective ownership */
        rcu_read_lock();
        cred = __task_cred(task);
        uid = cred->euid;
        gid = cred->egid;
        rcu_read_unlock();

        /*
         * Before the /proc/pid/status file was created the only way to read
         * the effective uid of a /process was to stat /proc/pid.  Reading
         * /proc/pid/status is slow enough that procps and other packages
         * kept stating /proc/pid.  To keep the rules in /proc simple I have
         * made this apply to all per process world readable and executable
         * directories.
         */
        if (mode != (S_IFDIR|S_IRUGO|S_IXUGO)) {
                struct mm_struct *mm;
                task_lock(task);
                mm = task->mm;
                /* Make non-dumpable tasks owned by some root */
                if (mm) {
                        if (get_dumpable(mm) != SUID_DUMP_USER) {
                                struct user_namespace *user_ns = mm->user_ns;

                                uid = make_kuid(user_ns, 0);
                                if (!uid_valid(uid))
                                        uid = GLOBAL_ROOT_UID;

                                gid = make_kgid(user_ns, 0);
                                if (!gid_valid(gid))
                                        gid = GLOBAL_ROOT_GID;
                        }
                } else {
                        uid = GLOBAL_ROOT_UID;
                        gid = GLOBAL_ROOT_GID;
                }
                task_unlock(task);
        }
        *ruid = uid;
        *rgid = gid;
}

void proc_pid_evict_inode(struct proc_inode *ei)
{
        struct pid *pid = ei->pid;

        if (S_ISDIR(ei->vfs_inode.i_mode)) {
                spin_lock(&pid->lock);
                hlist_del_init_rcu(&ei->sibling_inodes);
                spin_unlock(&pid->lock);
        }

        put_pid(pid);
}

struct inode *proc_pid_make_inode(struct super_block * sb,
                                  struct task_struct *task, umode_t mode)
{
        struct inode * inode;
        struct proc_inode *ei;
        struct pid *pid;

        /* We need a new inode */

        inode = new_inode(sb);
        if (!inode)
                goto out;

        /* Common stuff */
        ei = PROC_I(inode);
        inode->i_mode = mode;
        inode->i_ino = get_next_ino();
        inode->i_mtime = inode->i_atime = inode->i_ctime = current_time(inode);
        inode->i_op = &proc_def_inode_operations;

        /*
         * grab the reference to task.
         */
        pid = get_task_pid(task, PIDTYPE_PID);
        if (!pid)
                goto out_unlock;

        /* Let the pid remember us for quick removal */
        ei->pid = pid;
        if (S_ISDIR(mode)) {
                spin_lock(&pid->lock);
                hlist_add_head_rcu(&ei->sibling_inodes, &pid->inodes);
                spin_unlock(&pid->lock);
        }

        task_dump_owner(task, 0, &inode->i_uid, &inode->i_gid);
        security_task_to_inode(task, inode);

out:
        return inode;

out_unlock:
        iput(inode);
        return NULL;
}

int pid_getattr(const struct path *path, struct kstat *stat,
                u32 request_mask, unsigned int query_flags)
{
        struct inode *inode = d_inode(path->dentry);
        struct proc_fs_info *fs_info = proc_sb_info(inode->i_sb);
        struct task_struct *task;

        generic_fillattr(inode, stat);

        stat->uid = GLOBAL_ROOT_UID;
        stat->gid = GLOBAL_ROOT_GID;
        rcu_read_lock();
        task = pid_task(proc_pid(inode), PIDTYPE_PID);
        if (task) {
                if (!has_pid_permissions(fs_info, task, HIDEPID_INVISIBLE)) {
                        rcu_read_unlock();
                        /*
                         * This doesn't prevent learning whether PID exists,
                         * it only makes getattr() consistent with readdir().
                         */
                        return -ENOENT;
                }
                task_dump_owner(task, inode->i_mode, &stat->uid, &stat->gid);
        }
        rcu_read_unlock();
        return 0;
}

/* dentry stuff */

/*
 * Set <pid>/... inode ownership (can change due to setuid(), etc.)
 */
void pid_update_inode(struct task_struct *task, struct inode *inode)
{
        task_dump_owner(task, inode->i_mode, &inode->i_uid, &inode->i_gid);

        inode->i_mode &= ~(S_ISUID | S_ISGID);
        security_task_to_inode(task, inode);
}

/*
 * Rewrite the inode's ownerships here because the owning task may have
 * performed a setuid(), etc.
 *
 */
static int pid_revalidate(struct dentry *dentry, unsigned int flags)
{
        struct inode *inode;
        struct task_struct *task;

        if (flags & LOOKUP_RCU)
                return -ECHILD;

        inode = d_inode(dentry);
        task = get_proc_task(inode);

        if (task) {
                pid_update_inode(task, inode);
                put_task_struct(task);
                return 1;
        }
        return 0;
}

static inline bool proc_inode_is_dead(struct inode *inode)
{
        return !proc_pid(inode)->tasks[PIDTYPE_PID].first;
}

int pid_delete_dentry(const struct dentry *dentry)
{
        /* Is the task we represent dead?
         * If so, then don't put the dentry on the lru list,
         * kill it immediately.
         */
        return proc_inode_is_dead(d_inode(dentry));
}

const struct dentry_operations pid_dentry_operations =
{
        .d_revalidate   = pid_revalidate,
        .d_delete       = pid_delete_dentry,
};

/* Lookups */

/*
 * Fill a directory entry.
 *
 * If possible create the dcache entry and derive our inode number and
 * file type from dcache entry.
 *
 * Since all of the proc inode numbers are dynamically generated, the inode
 * numbers do not exist until the inode is cache.  This means creating the
 * the dcache entry in readdir is necessary to keep the inode numbers
 * reported by readdir in sync with the inode numbers reported
 * by stat.
 */
bool proc_fill_cache(struct file *file, struct dir_context *ctx,
        const char *name, unsigned int len,
        instantiate_t instantiate, struct task_struct *task, const void *ptr)
{
        struct dentry *child, *dir = file->f_path.dentry;
        struct qstr qname = QSTR_INIT(name, len);
        struct inode *inode;
        unsigned type = DT_UNKNOWN;
        ino_t ino = 1;

        child = d_hash_and_lookup(dir, &qname);
        if (!child) {
                DECLARE_WAIT_QUEUE_HEAD_ONSTACK(wq);
                child = d_alloc_parallel(dir, &qname, &wq);
                if (IS_ERR(child))
                        goto end_instantiate;
                if (d_in_lookup(child)) {
                        struct dentry *res;
                        res = instantiate(child, task, ptr);
                        d_lookup_done(child);
                        if (unlikely(res)) {
                                dput(child);
                                child = res;
                                if (IS_ERR(child))
                                        goto end_instantiate;
                        }
                }
        }
        inode = d_inode(child);
        ino = inode->i_ino;
        type = inode->i_mode >> 12;
        dput(child);
end_instantiate:
        return dir_emit(ctx, name, len, ino, type);
}

/*
 * dname_to_vma_addr - maps a dentry name into two unsigned longs
 * which represent vma start and end addresses.
 */
static int dname_to_vma_addr(struct dentry *dentry,
                             unsigned long *start, unsigned long *end)
{
        const char *str = dentry->d_name.name;
        unsigned long long sval, eval;
        unsigned int len;

        if (str[0] == '0' && str[1] != '-')
                return -EINVAL;
        len = _parse_integer(str, 16, &sval);
        if (len & KSTRTOX_OVERFLOW)
                return -EINVAL;
        if (sval != (unsigned long)sval)
                return -EINVAL;
        str += len;

        if (*str != '-')
                return -EINVAL;
        str++;

        if (str[0] == '0' && str[1])
                return -EINVAL;
        len = _parse_integer(str, 16, &eval);
        if (len & KSTRTOX_OVERFLOW)
                return -EINVAL;
        if (eval != (unsigned long)eval)
                return -EINVAL;
        str += len;

        if (*str != '\0')
                return -EINVAL;

        *start = sval;
        *end = eval;

        return 0;
}

static int map_files_d_revalidate(struct dentry *dentry, unsigned int flags)
{
        unsigned long vm_start, vm_end;
        bool exact_vma_exists = false;
        struct mm_struct *mm = NULL;
        struct task_struct *task;
        struct inode *inode;
        int status = 0;

        if (flags & LOOKUP_RCU)
                return -ECHILD;

        inode = d_inode(dentry);
        task = get_proc_task(inode);
        if (!task)
                goto out_notask;

        mm = mm_access(task, PTRACE_MODE_READ_FSCREDS);
        if (IS_ERR_OR_NULL(mm))
                goto out;

        if (!dname_to_vma_addr(dentry, &vm_start, &vm_end)) {
                status = down_read_killable(&mm->mmap_sem);
                if (!status) {
                        exact_vma_exists = !!find_exact_vma(mm, vm_start,
                                                            vm_end);
                        up_read(&mm->mmap_sem);
                }
        }

        mmput(mm);

        if (exact_vma_exists) {
                task_dump_owner(task, 0, &inode->i_uid, &inode->i_gid);

                security_task_to_inode(task, inode);
                status = 1;
        }

out:
        put_task_struct(task);

out_notask:
        return status;
}

static const struct dentry_operations tid_map_files_dentry_operations = {
        .d_revalidate   = map_files_d_revalidate,
        .d_delete       = pid_delete_dentry,
};

static int map_files_get_link(struct dentry *dentry, struct path *path)
{
        unsigned long vm_start, vm_end;
        struct vm_area_struct *vma;
        struct task_struct *task;
        struct mm_struct *mm;
        int rc;

        rc = -ENOENT;
        task = get_proc_task(d_inode(dentry));
        if (!task)
                goto out;

        mm = get_task_mm(task);
        put_task_struct(task);
        if (!mm)
                goto out;

        rc = dname_to_vma_addr(dentry, &vm_start, &vm_end);
        if (rc)
                goto out_mmput;

        rc = down_read_killable(&mm->mmap_sem);
        if (rc)
                goto out_mmput;

        rc = -ENOENT;
        vma = find_exact_vma(mm, vm_start, vm_end);
        if (vma && vma->vm_file) {
                *path = vma->vm_file->f_path;
                path_get(path);
                rc = 0;
        }
        up_read(&mm->mmap_sem);

out_mmput:
        mmput(mm);
out:
        return rc;
}

struct map_files_info {
        unsigned long   start;
        unsigned long   end;
        fmode_t         mode;
};

/*
 * Only allow CAP_SYS_ADMIN to follow the links, due to concerns about how the
 * symlinks may be used to bypass permissions on ancestor directories in the
 * path to the file in question.
 */
static const char *
proc_map_files_get_link(struct dentry *dentry,
                        struct inode *inode,
                        struct delayed_call *done)
{
        if (!capable(CAP_SYS_ADMIN))
                return ERR_PTR(-EPERM);

        return proc_pid_get_link(dentry, inode, done);
}

/*
 * Identical to proc_pid_link_inode_operations except for get_link()
 */
static const struct inode_operations proc_map_files_link_inode_operations = {
        .readlink       = proc_pid_readlink,
        .get_link       = proc_map_files_get_link,
        .setattr        = proc_setattr,
};

static struct dentry *
proc_map_files_instantiate(struct dentry *dentry,
                           struct task_struct *task, const void *ptr)
{
        fmode_t mode = (fmode_t)(unsigned long)ptr;
        struct proc_inode *ei;
        struct inode *inode;

        inode = proc_pid_make_inode(dentry->d_sb, task, S_IFLNK |
                                    ((mode & FMODE_READ ) ? S_IRUSR : 0) |
                                    ((mode & FMODE_WRITE) ? S_IWUSR : 0));
        if (!inode)
                return ERR_PTR(-ENOENT);

        ei = PROC_I(inode);
        ei->op.proc_get_link = map_files_get_link;

        inode->i_op = &proc_map_files_link_inode_operations;
        inode->i_size = 64;

        d_set_d_op(dentry, &tid_map_files_dentry_operations);
        return d_splice_alias(inode, dentry);
}

static struct dentry *proc_map_files_lookup(struct inode *dir,
                struct dentry *dentry, unsigned int flags)
{
        unsigned long vm_start, vm_end;
        struct vm_area_struct *vma;
        struct task_struct *task;
        struct dentry *result;
        struct mm_struct *mm;

        result = ERR_PTR(-ENOENT);
        task = get_proc_task(dir);
        if (!task)
                goto out;

        result = ERR_PTR(-EACCES);
        if (!ptrace_may_access(task, PTRACE_MODE_READ_FSCREDS))
                goto out_put_task;

        result = ERR_PTR(-ENOENT);
        if (dname_to_vma_addr(dentry, &vm_start, &vm_end))
                goto out_put_task;

        mm = get_task_mm(task);
        if (!mm)
                goto out_put_task;

        result = ERR_PTR(-EINTR);
        if (down_read_killable(&mm->mmap_sem))
                goto out_put_mm;

        result = ERR_PTR(-ENOENT);
        vma = find_exact_vma(mm, vm_start, vm_end);
        if (!vma)
                goto out_no_vma;

        if (vma->vm_file)
                result = proc_map_files_instantiate(dentry, task,
                                (void *)(unsigned long)vma->vm_file->f_mode);

out_no_vma:
        up_read(&mm->mmap_sem);
out_put_mm:
        mmput(mm);
out_put_task:
        put_task_struct(task);
out:
        return result;
}

static const struct inode_operations proc_map_files_inode_operations = {
        .lookup         = proc_map_files_lookup,
        .permission     = proc_fd_permission,
        .setattr        = proc_setattr,
};

static int
proc_map_files_readdir(struct file *file, struct dir_context *ctx)
{
        struct vm_area_struct *vma;
        struct task_struct *task;
        struct mm_struct *mm;
        unsigned long nr_files, pos, i;
        GENRADIX(struct map_files_info) fa;
        struct map_files_info *p;
        int ret;

        genradix_init(&fa);

        ret = -ENOENT;
        task = get_proc_task(file_inode(file));
        if (!task)
                goto out;

        ret = -EACCES;
        if (!ptrace_may_access(task, PTRACE_MODE_READ_FSCREDS))
                goto out_put_task;

        ret = 0;
        if (!dir_emit_dots(file, ctx))
                goto out_put_task;

        mm = get_task_mm(task);
        if (!mm)
                goto out_put_task;

        ret = down_read_killable(&mm->mmap_sem);
        if (ret) {
                mmput(mm);
                goto out_put_task;
        }

        nr_files = 0;

        /*
         * We need two passes here:
         *
         *  1) Collect vmas of mapped files with mmap_sem taken
         *  2) Release mmap_sem and instantiate entries
         *
         * otherwise we get lockdep complained, since filldir()
         * routine might require mmap_sem taken in might_fault().
         */

        for (vma = mm->mmap, pos = 2; vma; vma = vma->vm_next) {
                if (!vma->vm_file)
                        continue;
                if (++pos <= ctx->pos)
                        continue;

                p = genradix_ptr_alloc(&fa, nr_files++, GFP_KERNEL);
                if (!p) {
                        ret = -ENOMEM;
                        up_read(&mm->mmap_sem);
                        mmput(mm);
                        goto out_put_task;
                }

                p->start = vma->vm_start;
                p->end = vma->vm_end;
                p->mode = vma->vm_file->f_mode;
        }
        up_read(&mm->mmap_sem);
        mmput(mm);

        for (i = 0; i < nr_files; i++) {
                char buf[4 * sizeof(long) + 2]; /* max: %lx-%lx\0 */
                unsigned int len;

                p = genradix_ptr(&fa, i);
                len = snprintf(buf, sizeof(buf), "%lx-%lx", p->start, p->end);
                if (!proc_fill_cache(file, ctx,
                                      buf, len,
                                      proc_map_files_instantiate,
                                      task,
                                      (void *)(unsigned long)p->mode))
                        break;
                ctx->pos++;
        }

out_put_task:
        put_task_struct(task);
out:
        genradix_free(&fa);
        return ret;
}

static const struct file_operations proc_map_files_operations = {
        .read           = generic_read_dir,
        .iterate_shared = proc_map_files_readdir,
        .llseek         = generic_file_llseek,
};

#if defined(CONFIG_CHECKPOINT_RESTORE) && defined(CONFIG_POSIX_TIMERS)
struct timers_private {
        struct pid *pid;
        struct task_struct *task;
        struct sighand_struct *sighand;
        struct pid_namespace *ns;
        unsigned long flags;
};

static void *timers_start(struct seq_file *m, loff_t *pos)
{
        struct timers_private *tp = m->private;

        tp->task = get_pid_task(tp->pid, PIDTYPE_PID);
        if (!tp->task)
                return ERR_PTR(-ESRCH);

        tp->sighand = lock_task_sighand(tp->task, &tp->flags);
        if (!tp->sighand)
                return ERR_PTR(-ESRCH);

        return seq_list_start(&tp->task->signal->posix_timers, *pos);
}

static void *timers_next(struct seq_file *m, void *v, loff_t *pos)
{
        struct timers_private *tp = m->private;
        return seq_list_next(v, &tp->task->signal->posix_timers, pos);
}

static void timers_stop(struct seq_file *m, void *v)
{
        struct timers_private *tp = m->private;

        if (tp->sighand) {
                unlock_task_sighand(tp->task, &tp->flags);
                tp->sighand = NULL;
        }

        if (tp->task) {
                put_task_struct(tp->task);
                tp->task = NULL;
        }
}

static int show_timer(struct seq_file *m, void *v)
{
        struct k_itimer *timer;
        struct timers_private *tp = m->private;
        int notify;
        static const char * const nstr[] = {
                [SIGEV_SIGNAL] = "signal",
                [SIGEV_NONE] = "none",
                [SIGEV_THREAD] = "thread",
        };

        timer = list_entry((struct list_head *)v, struct k_itimer, list);
        notify = timer->it_sigev_notify;

        seq_printf(m, "ID: %d\n", timer->it_id);
        seq_printf(m, "signal: %d/%px\n",
                   timer->sigq->info.si_signo,
                   timer->sigq->info.si_value.sival_ptr);
        seq_printf(m, "notify: %s/%s.%d\n",
                   nstr[notify & ~SIGEV_THREAD_ID],
                   (notify & SIGEV_THREAD_ID) ? "tid" : "pid",
                   pid_nr_ns(timer->it_pid, tp->ns));
        seq_printf(m, "ClockID: %d\n", timer->it_clock);

        return 0;
}

static const struct seq_operations proc_timers_seq_ops = {
        .start  = timers_start,
        .next   = timers_next,
        .stop   = timers_stop,
        .show   = show_timer,
};

static int proc_timers_open(struct inode *inode, struct file *file)
{
        struct timers_private *tp;

        tp = __seq_open_private(file, &proc_timers_seq_ops,
                        sizeof(struct timers_private));
        if (!tp)
                return -ENOMEM;

        tp->pid = proc_pid(inode);
        tp->ns = proc_pid_ns(inode->i_sb);
        return 0;
}

static const struct file_operations proc_timers_operations = {
        .open           = proc_timers_open,
        .read           = seq_read,
        .llseek         = seq_lseek,
        .release        = seq_release_private,
};
#endif

static ssize_t timerslack_ns_write(struct file *file, const char __user *buf,
                                        size_t count, loff_t *offset)
{
        struct inode *inode = file_inode(file);
        struct task_struct *p;
        u64 slack_ns;
        int err;

        err = kstrtoull_from_user(buf, count, 10, &slack_ns);
        if (err < 0)
                return err;

        p = get_proc_task(inode);
        if (!p)
                return -ESRCH;

        if (p != current) {
                rcu_read_lock();
                if (!ns_capable(__task_cred(p)->user_ns, CAP_SYS_NICE)) {
                        rcu_read_unlock();
                        count = -EPERM;
                        goto out;
                }
                rcu_read_unlock();

                err = security_task_setscheduler(p);
                if (err) {
                        count = err;
                        goto out;
                }
        }

        task_lock(p);
        if (slack_ns == 0)
                p->timer_slack_ns = p->default_timer_slack_ns;
        else
                p->timer_slack_ns = slack_ns;
        task_unlock(p);

out:
        put_task_struct(p);

        return count;
}

static int timerslack_ns_show(struct seq_file *m, void *v)
{
        struct inode *inode = m->private;
        struct task_struct *p;
        int err = 0;

        p = get_proc_task(inode);
        if (!p)
                return -ESRCH;

        if (p != current) {
                rcu_read_lock();
                if (!ns_capable(__task_cred(p)->user_ns, CAP_SYS_NICE)) {
                        rcu_read_unlock();
                        err = -EPERM;
                        goto out;
                }
                rcu_read_unlock();

                err = security_task_getscheduler(p);
                if (err)
                        goto out;
        }

        task_lock(p);
        seq_printf(m, "%llu\n", p->timer_slack_ns);
        task_unlock(p);

out:
        put_task_struct(p);

        return err;
}

static int timerslack_ns_open(struct inode *inode, struct file *filp)
{
        return single_open(filp, timerslack_ns_show, inode);
}

static const struct file_operations proc_pid_set_timerslack_ns_operations = {
        .open           = timerslack_ns_open,
        .read           = seq_read,
        .write          = timerslack_ns_write,
        .llseek         = seq_lseek,
        .release        = single_release,
};

static struct dentry *proc_pident_instantiate(struct dentry *dentry,
        struct task_struct *task, const void *ptr)
{
        const struct pid_entry *p = ptr;
        struct inode *inode;
        struct proc_inode *ei;

        inode = proc_pid_make_inode(dentry->d_sb, task, p->mode);
        if (!inode)
                return ERR_PTR(-ENOENT);

        ei = PROC_I(inode);
        if (S_ISDIR(inode->i_mode))
                set_nlink(inode, 2);    /* Use getattr to fix if necessary */
        if (p->iop)
                inode->i_op = p->iop;
        if (p->fop)
                inode->i_fop = p->fop;
        ei->op = p->op;
        pid_update_inode(task, inode);
        d_set_d_op(dentry, &pid_dentry_operations);
        return d_splice_alias(inode, dentry);
}

static struct dentry *proc_pident_lookup(struct inode *dir, 
                                         struct dentry *dentry,
                                         const struct pid_entry *p,
                                         const struct pid_entry *end)
{
        struct task_struct *task = get_proc_task(dir);
        struct dentry *res = ERR_PTR(-ENOENT);

        if (!task)
                goto out_no_task;

        /*
         * Yes, it does not scale. And it should not. Don't add
         * new entries into /proc/<tgid>/ without very good reasons.
         */
        for (; p < end; p++) {
                if (p->len != dentry->d_name.len)
                        continue;
                if (!memcmp(dentry->d_name.name, p->name, p->len)) {
                        res = proc_pident_instantiate(dentry, task, p);
                        break;
                }
        }
        put_task_struct(task);
out_no_task:
        return res;
}

static int proc_pident_readdir(struct file *file, struct dir_context *ctx,
                const struct pid_entry *ents, unsigned int nents)
{
        struct task_struct *task = get_proc_task(file_inode(file));
        const struct pid_entry *p;

        if (!task)
                return -ENOENT;

        if (!dir_emit_dots(file, ctx))
                goto out;

        if (ctx->pos >= nents + 2)
                goto out;

        for (p = ents + (ctx->pos - 2); p < ents + nents; p++) {
                if (!proc_fill_cache(file, ctx, p->name, p->len,
                                proc_pident_instantiate, task, p))
                        break;
                ctx->pos++;
        }
out:
        put_task_struct(task);
        return 0;
}

#ifdef CONFIG_SECURITY
static ssize_t proc_pid_attr_read(struct file * file, char __user * buf,
                                  size_t count, loff_t *ppos)
{
        struct inode * inode = file_inode(file);
        char *p = NULL;
        ssize_t length;
        struct task_struct *task = get_proc_task(inode);

        if (!task)
                return -ESRCH;

        length = security_getprocattr(task, PROC_I(inode)->op.lsm,
                                      (char*)file->f_path.dentry->d_name.name,
                                      &p);
        put_task_struct(task);
        if (length > 0)
                length = simple_read_from_buffer(buf, count, ppos, p, length);
        kfree(p);
        return length;
}

static ssize_t proc_pid_attr_write(struct file * file, const char __user * buf,
                                   size_t count, loff_t *ppos)
{
        struct inode * inode = file_inode(file);
        struct task_struct *task;
        void *page;
        int rv;

        rcu_read_lock();
        task = pid_task(proc_pid(inode), PIDTYPE_PID);
        if (!task) {
                rcu_read_unlock();
                return -ESRCH;
        }
        /* A task may only write its own attributes. */
        if (current != task) {
                rcu_read_unlock();
                return -EACCES;
        }
        /* Prevent changes to overridden credentials. */
        if (current_cred() != current_real_cred()) {
                rcu_read_unlock();
                return -EBUSY;
        }
        rcu_read_unlock();

        if (count > PAGE_SIZE)
                count = PAGE_SIZE;

        /* No partial writes. */
        if (*ppos != 0)
                return -EINVAL;

        page = memdup_user(buf, count);
        if (IS_ERR(page)) {
                rv = PTR_ERR(page);
                goto out;
        }

        /* Guard against adverse ptrace interaction */
        rv = mutex_lock_interruptible(&current->signal->cred_guard_mutex);
        if (rv < 0)
                goto out_free;

        rv = security_setprocattr(PROC_I(inode)->op.lsm,
                                  file->f_path.dentry->d_name.name, page,
                                  count);
        mutex_unlock(&current->signal->cred_guard_mutex);
out_free:
        kfree(page);
out:
        return rv;
}

static const struct file_operations proc_pid_attr_operations = {
        .read           = proc_pid_attr_read,
        .write          = proc_pid_attr_write,
        .llseek         = generic_file_llseek,
};

#define LSM_DIR_OPS(LSM) \
static int proc_##LSM##_attr_dir_iterate(struct file *filp, \
                             struct dir_context *ctx) \
{ \
        return proc_pident_readdir(filp, ctx, \
                                   LSM##_attr_dir_stuff, \
                                   ARRAY_SIZE(LSM##_attr_dir_stuff)); \
} \
\
static const struct file_operations proc_##LSM##_attr_dir_ops = { \
        .read           = generic_read_dir, \
        .iterate        = proc_##LSM##_attr_dir_iterate, \
        .llseek         = default_llseek, \
}; \
\
static struct dentry *proc_##LSM##_attr_dir_lookup(struct inode *dir, \
                                struct dentry *dentry, unsigned int flags) \
{ \
        return proc_pident_lookup(dir, dentry, \
                                  LSM##_attr_dir_stuff, \
                                  LSM##_attr_dir_stuff + ARRAY_SIZE(LSM##_attr_dir_stuff)); \
} \
\
static const struct inode_operations proc_##LSM##_attr_dir_inode_ops = { \
        .lookup         = proc_##LSM##_attr_dir_lookup, \
        .getattr        = pid_getattr, \
        .setattr        = proc_setattr, \
}

#ifdef CONFIG_SECURITY_SMACK
static const struct pid_entry smack_attr_dir_stuff[] = {
        ATTR("smack", "current",        0666),
};
LSM_DIR_OPS(smack);
#endif

static const struct pid_entry attr_dir_stuff[] = {
        ATTR(NULL, "current",           0666),
        ATTR(NULL, "prev",              0444),
        ATTR(NULL, "exec",              0666),
        ATTR(NULL, "fscreate",          0666),
        ATTR(NULL, "keycreate",         0666),
        ATTR(NULL, "sockcreate",        0666),
#ifdef CONFIG_SECURITY_SMACK
        DIR("smack",                    0555,
            proc_smack_attr_dir_inode_ops, proc_smack_attr_dir_ops),
#endif
};

static int proc_attr_dir_readdir(struct file *file, struct dir_context *ctx)
{
        return proc_pident_readdir(file, ctx, 
                                   attr_dir_stuff, ARRAY_SIZE(attr_dir_stuff));
}

static const struct file_operations proc_attr_dir_operations = {
        .read           = generic_read_dir,
        .iterate_shared = proc_attr_dir_readdir,
        .llseek         = generic_file_llseek,
};

static struct dentry *proc_attr_dir_lookup(struct inode *dir,
                                struct dentry *dentry, unsigned int flags)
{
        return proc_pident_lookup(dir, dentry,
                                  attr_dir_stuff,
                                  attr_dir_stuff + ARRAY_SIZE(attr_dir_stuff));
}

static const struct inode_operations proc_attr_dir_inode_operations = {
        .lookup         = proc_attr_dir_lookup,
        .getattr        = pid_getattr,
        .setattr        = proc_setattr,
};

#endif

#ifdef CONFIG_ELF_CORE
static ssize_t proc_coredump_filter_read(struct file *file, char __user *buf,
                                         size_t count, loff_t *ppos)
{
        struct task_struct *task = get_proc_task(file_inode(file));
        struct mm_struct *mm;
        char buffer[PROC_NUMBUF];
        size_t len;
        int ret;

        if (!task)
                return -ESRCH;

        ret = 0;
        mm = get_task_mm(task);
        if (mm) {
                len = snprintf(buffer, sizeof(buffer), "%08lx\n",
                               ((mm->flags & MMF_DUMP_FILTER_MASK) >>
                                MMF_DUMP_FILTER_SHIFT));
                mmput(mm);
                ret = simple_read_from_buffer(buf, count, ppos, buffer, len);
        }

        put_task_struct(task);

        return ret;
}

static ssize_t proc_coredump_filter_write(struct file *file,
                                          const char __user *buf,
                                          size_t count,
                                          loff_t *ppos)
{
        struct task_struct *task;
        struct mm_struct *mm;
        unsigned int val;
        int ret;
        int i;
        unsigned long mask;

        ret = kstrtouint_from_user(buf, count, 0, &val);
        if (ret < 0)
                return ret;

        ret = -ESRCH;
        task = get_proc_task(file_inode(file));
        if (!task)
                goto out_no_task;

        mm = get_task_mm(task);
        if (!mm)
                goto out_no_mm;
        ret = 0;

        for (i = 0, mask = 1; i < MMF_DUMP_FILTER_BITS; i++, mask <<= 1) {
                if (val & mask)
                        set_bit(i + MMF_DUMP_FILTER_SHIFT, &mm->flags);
                else
                        clear_bit(i + MMF_DUMP_FILTER_SHIFT, &mm->flags);
        }

        mmput(mm);
 out_no_mm:
        put_task_struct(task);
 out_no_task:
        if (ret < 0)
                return ret;
        return count;
}

static const struct file_operations proc_coredump_filter_operations = {
        .read           = proc_coredump_filter_read,
        .write          = proc_coredump_filter_write,
        .llseek         = generic_file_llseek,
};
#endif

#ifdef CONFIG_TASK_IO_ACCOUNTING
static int do_io_accounting(struct task_struct *task, struct seq_file *m, int whole)
{
        struct task_io_accounting acct = task->ioac;
        unsigned long flags;
        int result;

        result = mutex_lock_killable(&task->signal->exec_update_mutex);
        if (result)
                return result;

        if (!ptrace_may_access(task, PTRACE_MODE_READ_FSCREDS)) {
                result = -EACCES;
                goto out_unlock;
        }

        if (whole && lock_task_sighand(task, &flags)) {
                struct task_struct *t = task;

                task_io_accounting_add(&acct, &task->signal->ioac);
                while_each_thread(task, t)
                        task_io_accounting_add(&acct, &t->ioac);

                unlock_task_sighand(task, &flags);
        }
        seq_printf(m,
                   "rchar: %llu\n"
                   "wchar: %llu\n"
                   "syscr: %llu\n"
                   "syscw: %llu\n"
                   "read_bytes: %llu\n"
                   "write_bytes: %llu\n"
                   "cancelled_write_bytes: %llu\n",
                   (unsigned long long)acct.rchar,
                   (unsigned long long)acct.wchar,
                   (unsigned long long)acct.syscr,
                   (unsigned long long)acct.syscw,
                   (unsigned long long)acct.read_bytes,
                   (unsigned long long)acct.write_bytes,
                   (unsigned long long)acct.cancelled_write_bytes);
        result = 0;

out_unlock:
        mutex_unlock(&task->signal->exec_update_mutex);
        return result;
}

static int proc_tid_io_accounting(struct seq_file *m, struct pid_namespace *ns,
                                  struct pid *pid, struct task_struct *task)
{
        return do_io_accounting(task, m, 0);
}

static int proc_tgid_io_accounting(struct seq_file *m, struct pid_namespace *ns,
                                   struct pid *pid, struct task_struct *task)
{
        return do_io_accounting(task, m, 1);
}
#endif /* CONFIG_TASK_IO_ACCOUNTING */

#ifdef CONFIG_USER_NS
static int proc_id_map_open(struct inode *inode, struct file *file,
        const struct seq_operations *seq_ops)
{
        struct user_namespace *ns = NULL;
        struct task_struct *task;
        struct seq_file *seq;
        int ret = -EINVAL;

        task = get_proc_task(inode);
        if (task) {
                rcu_read_lock();
                ns = get_user_ns(task_cred_xxx(task, user_ns));
                rcu_read_unlock();
                put_task_struct(task);
        }
        if (!ns)
                goto err;

        ret = seq_open(file, seq_ops);
        if (ret)
                goto err_put_ns;

        seq = file->private_data;
        seq->private = ns;

        return 0;
err_put_ns:
        put_user_ns(ns);
err:
        return ret;
}

static int proc_id_map_release(struct inode *inode, struct file *file)
{
        struct seq_file *seq = file->private_data;
        struct user_namespace *ns = seq->private;
        put_user_ns(ns);
        return seq_release(inode, file);
}

static int proc_uid_map_open(struct inode *inode, struct file *file)
{
        return proc_id_map_open(inode, file, &proc_uid_seq_operations);
}

static int proc_gid_map_open(struct inode *inode, struct file *file)
{
        return proc_id_map_open(inode, file, &proc_gid_seq_operations);
}

static int proc_projid_map_open(struct inode *inode, struct file *file)
{
        return proc_id_map_open(inode, file, &proc_projid_seq_operations);
}

static const struct file_operations proc_uid_map_operations = {
        .open           = proc_uid_map_open,
        .write          = proc_uid_map_write,
        .read           = seq_read,
        .llseek         = seq_lseek,
        .release        = proc_id_map_release,
};

static const struct file_operations proc_gid_map_operations = {
        .open           = proc_gid_map_open,
        .write          = proc_gid_map_write,
        .read           = seq_read,
        .llseek         = seq_lseek,
        .release        = proc_id_map_release,
};

static const struct file_operations proc_projid_map_operations = {
        .open           = proc_projid_map_open,
        .write          = proc_projid_map_write,
        .read           = seq_read,
        .llseek         = seq_lseek,
        .release        = proc_id_map_release,
};

static int proc_setgroups_open(struct inode *inode, struct file *file)
{
        struct user_namespace *ns = NULL;
        struct task_struct *task;
        int ret;

        ret = -ESRCH;
        task = get_proc_task(inode);
        if (task) {
                rcu_read_lock();
                ns = get_user_ns(task_cred_xxx(task, user_ns));
                rcu_read_unlock();
                put_task_struct(task);
        }
        if (!ns)
                goto err;

        if (file->f_mode & FMODE_WRITE) {
                ret = -EACCES;
                if (!ns_capable(ns, CAP_SYS_ADMIN))
                        goto err_put_ns;
        }

        ret = single_open(file, &proc_setgroups_show, ns);
        if (ret)
                goto err_put_ns;

        return 0;
err_put_ns:
        put_user_ns(ns);
err:
        return ret;
}

static int proc_setgroups_release(struct inode *inode, struct file *file)
{
        struct seq_file *seq = file->private_data;
        struct user_namespace *ns = seq->private;
        int ret = single_release(inode, file);
        put_user_ns(ns);
        return ret;
}

static const struct file_operations proc_setgroups_operations = {
        .open           = proc_setgroups_open,
        .write          = proc_setgroups_write,
        .read           = seq_read,
        .llseek         = seq_lseek,
        .release        = proc_setgroups_release,
};
#endif /* CONFIG_USER_NS */

static int proc_pid_personality(struct seq_file *m, struct pid_namespace *ns,
                                struct pid *pid, struct task_struct *task)
{
        int err = lock_trace(task);
        if (!err) {
                seq_printf(m, "%08x\n", task->personality);
                unlock_trace(task);
        }
        return err;
}

#ifdef CONFIG_LIVEPATCH
static int proc_pid_patch_state(struct seq_file *m, struct pid_namespace *ns,
                                struct pid *pid, struct task_struct *task)
{
        seq_printf(m, "%d\n", task->patch_state);
        return 0;
}
#endif /* CONFIG_LIVEPATCH */

#ifdef CONFIG_STACKLEAK_METRICS
static int proc_stack_depth(struct seq_file *m, struct pid_namespace *ns,
                                struct pid *pid, struct task_struct *task)
{
        unsigned long prev_depth = THREAD_SIZE -
                                (task->prev_lowest_stack & (THREAD_SIZE - 1));
        unsigned long depth = THREAD_SIZE -
                                (task->lowest_stack & (THREAD_SIZE - 1));

        seq_printf(m, "previous stack depth: %lu\nstack depth: %lu\n",
                                                        prev_depth, depth);
        return 0;
}
#endif /* CONFIG_STACKLEAK_METRICS */

/*
 * Thread groups
 */
static const struct file_operations proc_task_operations;
static const struct inode_operations proc_task_inode_operations;

static const struct pid_entry tgid_base_stuff[] = {
        DIR("task",       S_IRUGO|S_IXUGO, proc_task_inode_operations, proc_task_operations),
        DIR("fd",         S_IRUSR|S_IXUSR, proc_fd_inode_operations, proc_fd_operations),
        DIR("map_files",  S_IRUSR|S_IXUSR, proc_map_files_inode_operations, proc_map_files_operations),
        DIR("fdinfo",     S_IRUSR|S_IXUSR, proc_fdinfo_inode_operations, proc_fdinfo_operations),
        DIR("ns",         S_IRUSR|S_IXUGO, proc_ns_dir_inode_operations, proc_ns_dir_operations),
#ifdef CONFIG_NET
        DIR("net",        S_IRUGO|S_IXUGO, proc_net_inode_operations, proc_net_operations),
#endif
        REG("environ",    S_IRUSR, proc_environ_operations),
        REG("auxv",       S_IRUSR, proc_auxv_operations),
        ONE("status",     S_IRUGO, proc_pid_status),
        ONE("personality", S_IRUSR, proc_pid_personality),
        ONE("limits",     S_IRUGO, proc_pid_limits),
#ifdef CONFIG_SCHED_DEBUG
        REG("sched",      S_IRUGO|S_IWUSR, proc_pid_sched_operations),
#endif
#ifdef CONFIG_SCHED_AUTOGROUP
        REG("autogroup",  S_IRUGO|S_IWUSR, proc_pid_sched_autogroup_operations),
#endif
#ifdef CONFIG_TIME_NS
        REG("timens_offsets",  S_IRUGO|S_IWUSR, proc_timens_offsets_operations),
#endif
        REG("comm",      S_IRUGO|S_IWUSR, proc_pid_set_comm_operations),
#ifdef CONFIG_HAVE_ARCH_TRACEHOOK
        ONE("syscall",    S_IRUSR, proc_pid_syscall),
#endif
        REG("cmdline",    S_IRUGO, proc_pid_cmdline_ops),
        ONE("stat",       S_IRUGO, proc_tgid_stat),
        ONE("statm",      S_IRUGO, proc_pid_statm),
        REG("maps",       S_IRUGO, proc_pid_maps_operations),
#ifdef CONFIG_NUMA
        REG("numa_maps",  S_IRUGO, proc_pid_numa_maps_operations),
#endif
        REG("mem",        S_IRUSR|S_IWUSR, proc_mem_operations),
        LNK("cwd",        proc_cwd_link),
        LNK("root",       proc_root_link),
        LNK("exe",        proc_exe_link),
        REG("mounts",     S_IRUGO, proc_mounts_operations),
        REG("mountinfo",  S_IRUGO, proc_mountinfo_operations),
        REG("mountstats", S_IRUSR, proc_mountstats_operations),
#ifdef CONFIG_PROC_PAGE_MONITOR
        REG("clear_refs", S_IWUSR, proc_clear_refs_operations),
        REG("smaps",      S_IRUGO, proc_pid_smaps_operations),
        REG("smaps_rollup", S_IRUGO, proc_pid_smaps_rollup_operations),
        REG("pagemap",    S_IRUSR, proc_pagemap_operations),
#endif
#ifdef CONFIG_SECURITY
        DIR("attr",       S_IRUGO|S_IXUGO, proc_attr_dir_inode_operations, proc_attr_dir_operations),
#endif
#ifdef CONFIG_KALLSYMS
        ONE("wchan",      S_IRUGO, proc_pid_wchan),
#endif
#ifdef CONFIG_STACKTRACE
        ONE("stack",      S_IRUSR, proc_pid_stack),
#endif
#ifdef CONFIG_SCHED_INFO
        ONE("schedstat",  S_IRUGO, proc_pid_schedstat),
#endif
#ifdef CONFIG_LATENCYTOP
        REG("latency",  S_IRUGO, proc_lstats_operations),
#endif
#ifdef CONFIG_PROC_PID_CPUSET
        ONE("cpuset",     S_IRUGO, proc_cpuset_show),
#endif
#ifdef CONFIG_CGROUPS
        ONE("cgroup",  S_IRUGO, proc_cgroup_show),
#endif
#ifdef CONFIG_PROC_CPU_RESCTRL
        ONE("cpu_resctrl_groups", S_IRUGO, proc_resctrl_show),
#endif
        ONE("oom_score",  S_IRUGO, proc_oom_score),
        REG("oom_adj",    S_IRUGO|S_IWUSR, proc_oom_adj_operations),
        REG("oom_score_adj", S_IRUGO|S_IWUSR, proc_oom_score_adj_operations),
#ifdef CONFIG_AUDIT
        REG("loginuid",   S_IWUSR|S_IRUGO, proc_loginuid_operations),
        REG("sessionid",  S_IRUGO, proc_sessionid_operations),
#endif
#ifdef CONFIG_FAULT_INJECTION
        REG("make-it-fail", S_IRUGO|S_IWUSR, proc_fault_inject_operations),
        REG("fail-nth", 0644, proc_fail_nth_operations),
#endif
#ifdef CONFIG_ELF_CORE
        REG("coredump_filter", S_IRUGO|S_IWUSR, proc_coredump_filter_operations),
#endif
#ifdef CONFIG_TASK_IO_ACCOUNTING
        ONE("io",       S_IRUSR, proc_tgid_io_accounting),
#endif
#ifdef CONFIG_USER_NS
        REG("uid_map",    S_IRUGO|S_IWUSR, proc_uid_map_operations),
        REG("gid_map",    S_IRUGO|S_IWUSR, proc_gid_map_operations),
        REG("projid_map", S_IRUGO|S_IWUSR, proc_projid_map_operations),
        REG("setgroups",  S_IRUGO|S_IWUSR, proc_setgroups_operations),
#endif
#if defined(CONFIG_CHECKPOINT_RESTORE) && defined(CONFIG_POSIX_TIMERS)
        REG("timers",     S_IRUGO, proc_timers_operations),
#endif
        REG("timerslack_ns", S_IRUGO|S_IWUGO, proc_pid_set_timerslack_ns_operations),
#ifdef CONFIG_LIVEPATCH
        ONE("patch_state",  S_IRUSR, proc_pid_patch_state),
#endif
#ifdef CONFIG_STACKLEAK_METRICS
        ONE("stack_depth", S_IRUGO, proc_stack_depth),
#endif
#ifdef CONFIG_PROC_PID_ARCH_STATUS
        ONE("arch_status", S_IRUGO, proc_pid_arch_status),
#endif
};

static int proc_tgid_base_readdir(struct file *file, struct dir_context *ctx)
{
        return proc_pident_readdir(file, ctx,
                                   tgid_base_stuff, ARRAY_SIZE(tgid_base_stuff));
}

static const struct file_operations proc_tgid_base_operations = {
        .read           = generic_read_dir,
        .iterate_shared = proc_tgid_base_readdir,
        .llseek         = generic_file_llseek,
};

struct pid *tgid_pidfd_to_pid(const struct file *file)
{
        if (file->f_op != &proc_tgid_base_operations)
                return ERR_PTR(-EBADF);

        return proc_pid(file_inode(file));
}

static struct dentry *proc_tgid_base_lookup(struct inode *dir, struct dentry *dentry, unsigned int flags)
{
        return proc_pident_lookup(dir, dentry,
                                  tgid_base_stuff,
                                  tgid_base_stuff + ARRAY_SIZE(tgid_base_stuff));
}

static const struct inode_operations proc_tgid_base_inode_operations = {
        .lookup         = proc_tgid_base_lookup,
        .getattr        = pid_getattr,
        .setattr        = proc_setattr,
        .permission     = proc_pid_permission,
};

/**
 * proc_flush_pid -  Remove dcache entries for @pid from the /proc dcache.
 * @pid: pid that should be flushed.
 *
 * This function walks a list of inodes (that belong to any proc
 * filesystem) that are attached to the pid and flushes them from
 * the dentry cache.
 *
 * It is safe and reasonable to cache /proc entries for a task until
 * that task exits.  After that they just clog up the dcache with
 * useless entries, possibly causing useful dcache entries to be
 * flushed instead.  This routine is provided to flush those useless
 * dcache entries when a process is reaped.
 *
 * NOTE: This routine is just an optimization so it does not guarantee
 *       that no dcache entries will exist after a process is reaped
 *       it just makes it very unlikely that any will persist.
 */

void proc_flush_pid(struct pid *pid)
{
        proc_invalidate_siblings_dcache(&pid->inodes, &pid->lock);
}

static struct dentry *proc_pid_instantiate(struct dentry * dentry,
                                   struct task_struct *task, const void *ptr)
{
        struct inode *inode;

        inode = proc_pid_make_inode(dentry->d_sb, task, S_IFDIR | S_IRUGO | S_IXUGO);
        if (!inode)
                return ERR_PTR(-ENOENT);

        inode->i_op = &proc_tgid_base_inode_operations;
        inode->i_fop = &proc_tgid_base_operations;
        inode->i_flags|=S_IMMUTABLE;

        set_nlink(inode, nlink_tgid);
        pid_update_inode(task, inode);

        d_set_d_op(dentry, &pid_dentry_operations);
        return d_splice_alias(inode, dentry);
}

struct dentry *proc_pid_lookup(struct dentry *dentry, unsigned int flags)
{
        struct task_struct *task;
        unsigned tgid;
        struct proc_fs_info *fs_info;
        struct pid_namespace *ns;
        struct dentry *result = ERR_PTR(-ENOENT);

        tgid = name_to_int(&dentry->d_name);
        if (tgid == ~0U)
                goto out;

        fs_info = proc_sb_info(dentry->d_sb);
        ns = fs_info->pid_ns;
        rcu_read_lock();
        task = find_task_by_pid_ns(tgid, ns);
        if (task)
                get_task_struct(task);
        rcu_read_unlock();
        if (!task)
                goto out;

        /* Limit procfs to only ptraceable tasks */
        if (fs_info->hide_pid == HIDEPID_NOT_PTRACEABLE) {
                if (!has_pid_permissions(fs_info, task, HIDEPID_NO_ACCESS))
                        goto out_put_task;
        }

        result = proc_pid_instantiate(dentry, task, NULL);
out_put_task:
        put_task_struct(task);
out:
        return result;
}

/*
 * Find the first task with tgid >= tgid
 *
 */
struct tgid_iter {
        unsigned int tgid;
        struct task_struct *task;
};
static struct tgid_iter next_tgid(struct pid_namespace *ns, struct tgid_iter iter)
{
        struct pid *pid;

        if (iter.task)
                put_task_struct(iter.task);
        rcu_read_lock();
retry:
        iter.task = NULL;
        pid = find_ge_pid(iter.tgid, ns);
        if (pid) {
                iter.tgid = pid_nr_ns(pid, ns);
                iter.task = pid_task(pid, PIDTYPE_TGID);
                if (!iter.task) {
                        iter.tgid += 1;
                        goto retry;
                }
                get_task_struct(iter.task);
        }
        rcu_read_unlock();
        return iter;
}

#define TGID_OFFSET (FIRST_PROCESS_ENTRY + 2)

/* for the /proc/ directory itself, after non-process stuff has been done */
int proc_pid_readdir(struct file *file, struct dir_context *ctx)
{
        struct tgid_iter iter;
        struct proc_fs_info *fs_info = proc_sb_info(file_inode(file)->i_sb);
        struct pid_namespace *ns = proc_pid_ns(file_inode(file)->i_sb);
        loff_t pos = ctx->pos;

        if (pos >= PID_MAX_LIMIT + TGID_OFFSET)
                return 0;

        if (pos == TGID_OFFSET - 2) {
                struct inode *inode = d_inode(fs_info->proc_self);
                if (!dir_emit(ctx, "self", 4, inode->i_ino, DT_LNK))
                        return 0;
                ctx->pos = pos = pos + 1;
        }
        if (pos == TGID_OFFSET - 1) {
                struct inode *inode = d_inode(fs_info->proc_thread_self);
                if (!dir_emit(ctx, "thread-self", 11, inode->i_ino, DT_LNK))
                        return 0;
                ctx->pos = pos = pos + 1;
        }
        iter.tgid = pos - TGID_OFFSET;
        iter.task = NULL;
        for (iter = next_tgid(ns, iter);
             iter.task;
             iter.tgid += 1, iter = next_tgid(ns, iter)) {
                char name[10 + 1];
                unsigned int len;

                cond_resched();
                if (!has_pid_permissions(fs_info, iter.task, HIDEPID_INVISIBLE))
                        continue;

                len = snprintf(name, sizeof(name), "%u", iter.tgid);
                ctx->pos = iter.tgid + TGID_OFFSET;
                if (!proc_fill_cache(file, ctx, name, len,
                                     proc_pid_instantiate, iter.task, NULL)) {
                        put_task_struct(iter.task);
                        return 0;
                }
        }
        ctx->pos = PID_MAX_LIMIT + TGID_OFFSET;
        return 0;
}

/*
 * proc_tid_comm_permission is a special permission function exclusively
 * used for the node /proc/<pid>/task/<tid>/comm.
 * It bypasses generic permission checks in the case where a task of the same
 * task group attempts to access the node.
 * The rationale behind this is that glibc and bionic access this node for
 * cross thread naming (pthread_set/getname_np(!self)). However, if
 * PR_SET_DUMPABLE gets set to 0 this node among others becomes uid=0 gid=0,
 * which locks out the cross thread naming implementation.
 * This function makes sure that the node is always accessible for members of
 * same thread group.
 */
static int proc_tid_comm_permission(struct inode *inode, int mask)
{
        bool is_same_tgroup;
        struct task_struct *task;

        task = get_proc_task(inode);
        if (!task)
                return -ESRCH;
        is_same_tgroup = same_thread_group(current, task);
        put_task_struct(task);

        if (likely(is_same_tgroup && !(mask & MAY_EXEC))) {
                /* This file (/proc/<pid>/task/<tid>/comm) can always be
                 * read or written by the members of the corresponding
                 * thread group.
                 */
                return 0;
        }

        return generic_permission(inode, mask);
}

static const struct inode_operations proc_tid_comm_inode_operations = {
                .permission = proc_tid_comm_permission,
};

/*
 * Tasks
 */
static const struct pid_entry tid_base_stuff[] = {
        DIR("fd",        S_IRUSR|S_IXUSR, proc_fd_inode_operations, proc_fd_operations),
        DIR("fdinfo",    S_IRUSR|S_IXUSR, proc_fdinfo_inode_operations, proc_fdinfo_operations),
        DIR("ns",        S_IRUSR|S_IXUGO, proc_ns_dir_inode_operations, proc_ns_dir_operations),
#ifdef CONFIG_NET
        DIR("net",        S_IRUGO|S_IXUGO, proc_net_inode_operations, proc_net_operations),
#endif
        REG("environ",   S_IRUSR, proc_environ_operations),
        REG("auxv",      S_IRUSR, proc_auxv_operations),
        ONE("status",    S_IRUGO, proc_pid_status),
        ONE("personality", S_IRUSR, proc_pid_personality),
        ONE("limits",    S_IRUGO, proc_pid_limits),
#ifdef CONFIG_SCHED_DEBUG
        REG("sched",     S_IRUGO|S_IWUSR, proc_pid_sched_operations),
#endif
        NOD("comm",      S_IFREG|S_IRUGO|S_IWUSR,
                         &proc_tid_comm_inode_operations,
                         &proc_pid_set_comm_operations, {}),
#ifdef CONFIG_HAVE_ARCH_TRACEHOOK
        ONE("syscall",   S_IRUSR, proc_pid_syscall),
#endif
        REG("cmdline",   S_IRUGO, proc_pid_cmdline_ops),
        ONE("stat",      S_IRUGO, proc_tid_stat),
        ONE("statm",     S_IRUGO, proc_pid_statm),
        REG("maps",      S_IRUGO, proc_pid_maps_operations),
#ifdef CONFIG_PROC_CHILDREN
        REG("children",  S_IRUGO, proc_tid_children_operations),
#endif
#ifdef CONFIG_NUMA
        REG("numa_maps", S_IRUGO, proc_pid_numa_maps_operations),
#endif
        REG("mem",       S_IRUSR|S_IWUSR, proc_mem_operations),
        LNK("cwd",       proc_cwd_link),
        LNK("root",      proc_root_link),
        LNK("exe",       proc_exe_link),
        REG("mounts",    S_IRUGO, proc_mounts_operations),
        REG("mountinfo",  S_IRUGO, proc_mountinfo_operations),
#ifdef CONFIG_PROC_PAGE_MONITOR
        REG("clear_refs", S_IWUSR, proc_clear_refs_operations),
        REG("smaps",     S_IRUGO, proc_pid_smaps_operations),
        REG("smaps_rollup", S_IRUGO, proc_pid_smaps_rollup_operations),
        REG("pagemap",    S_IRUSR, proc_pagemap_operations),
#endif
#ifdef CONFIG_SECURITY
        DIR("attr",      S_IRUGO|S_IXUGO, proc_attr_dir_inode_operations, proc_attr_dir_operations),
#endif
#ifdef CONFIG_KALLSYMS
        ONE("wchan",     S_IRUGO, proc_pid_wchan),
#endif
#ifdef CONFIG_STACKTRACE
        ONE("stack",      S_IRUSR, proc_pid_stack),
#endif
#ifdef CONFIG_SCHED_INFO
        ONE("schedstat", S_IRUGO, proc_pid_schedstat),
#endif
#ifdef CONFIG_LATENCYTOP
        REG("latency",  S_IRUGO, proc_lstats_operations),
#endif
#ifdef CONFIG_PROC_PID_CPUSET
        ONE("cpuset",    S_IRUGO, proc_cpuset_show),
#endif
#ifdef CONFIG_CGROUPS
        ONE("cgroup",  S_IRUGO, proc_cgroup_show),
#endif
#ifdef CONFIG_PROC_CPU_RESCTRL
        ONE("cpu_resctrl_groups", S_IRUGO, proc_resctrl_show),
#endif
        ONE("oom_score", S_IRUGO, proc_oom_score),
        REG("oom_adj",   S_IRUGO|S_IWUSR, proc_oom_adj_operations),
        REG("oom_score_adj", S_IRUGO|S_IWUSR, proc_oom_score_adj_operations),
#ifdef CONFIG_AUDIT
        REG("loginuid",  S_IWUSR|S_IRUGO, proc_loginuid_operations),
        REG("sessionid",  S_IRUGO, proc_sessionid_operations),
#endif
#ifdef CONFIG_FAULT_INJECTION
        REG("make-it-fail", S_IRUGO|S_IWUSR, proc_fault_inject_operations),
        REG("fail-nth", 0644, proc_fail_nth_operations),
#endif
#ifdef CONFIG_TASK_IO_ACCOUNTING
        ONE("io",       S_IRUSR, proc_tid_io_accounting),
#endif
#ifdef CONFIG_USER_NS
        REG("uid_map",    S_IRUGO|S_IWUSR, proc_uid_map_operations),
        REG("gid_map",    S_IRUGO|S_IWUSR, proc_gid_map_operations),
        REG("projid_map", S_IRUGO|S_IWUSR, proc_projid_map_operations),
        REG("setgroups",  S_IRUGO|S_IWUSR, proc_setgroups_operations),
#endif
#ifdef CONFIG_LIVEPATCH
        ONE("patch_state",  S_IRUSR, proc_pid_patch_state),
#endif
#ifdef CONFIG_PROC_PID_ARCH_STATUS
        ONE("arch_status", S_IRUGO, proc_pid_arch_status),
#endif
};

static int proc_tid_base_readdir(struct file *file, struct dir_context *ctx)
{
        return proc_pident_readdir(file, ctx,
                                   tid_base_stuff, ARRAY_SIZE(tid_base_stuff));
}

static struct dentry *proc_tid_base_lookup(struct inode *dir, struct dentry *dentry, unsigned int flags)
{
        return proc_pident_lookup(dir, dentry,
                                  tid_base_stuff,
                                  tid_base_stuff + ARRAY_SIZE(tid_base_stuff));
}

static const struct file_operations proc_tid_base_operations = {
        .read           = generic_read_dir,
        .iterate_shared = proc_tid_base_readdir,
        .llseek         = generic_file_llseek,
};

static const struct inode_operations proc_tid_base_inode_operations = {
        .lookup         = proc_tid_base_lookup,
        .getattr        = pid_getattr,
        .setattr        = proc_setattr,
};

static struct dentry *proc_task_instantiate(struct dentry *dentry,
        struct task_struct *task, const void *ptr)
{
        struct inode *inode;
        inode = proc_pid_make_inode(dentry->d_sb, task, S_IFDIR | S_IRUGO | S_IXUGO);
        if (!inode)
                return ERR_PTR(-ENOENT);

        inode->i_op = &proc_tid_base_inode_operations;
        inode->i_fop = &proc_tid_base_operations;
        inode->i_flags |= S_IMMUTABLE;

        set_nlink(inode, nlink_tid);
        pid_update_inode(task, inode);

        d_set_d_op(dentry, &pid_dentry_operations);
        return d_splice_alias(inode, dentry);
}

static struct dentry *proc_task_lookup(struct inode *dir, struct dentry * dentry, unsigned int flags)
{
        struct task_struct *task;
        struct task_struct *leader = get_proc_task(dir);
        unsigned tid;
        struct proc_fs_info *fs_info;
        struct pid_namespace *ns;
        struct dentry *result = ERR_PTR(-ENOENT);

        if (!leader)
                goto out_no_task;

        tid = name_to_int(&dentry->d_name);
        if (tid == ~0U)
                goto out;

        fs_info = proc_sb_info(dentry->d_sb);
        ns = fs_info->pid_ns;
        rcu_read_lock();
        task = find_task_by_pid_ns(tid, ns);
        if (task)
                get_task_struct(task);
        rcu_read_unlock();
        if (!task)
                goto out;
        if (!same_thread_group(leader, task))
                goto out_drop_task;

        result = proc_task_instantiate(dentry, task, NULL);
out_drop_task:
        put_task_struct(task);
out:
        put_task_struct(leader);
out_no_task:
        return result;
}

/*
 * Find the first tid of a thread group to return to user space.
 *
 * Usually this is just the thread group leader, but if the users
 * buffer was too small or there was a seek into the middle of the
 * directory we have more work todo.
 *
 * In the case of a short read we start with find_task_by_pid.
 *
 * In the case of a seek we start with the leader and walk nr
 * threads past it.
 */
static struct task_struct *first_tid(struct pid *pid, int tid, loff_t f_pos,
                                        struct pid_namespace *ns)
{
        struct task_struct *pos, *task;
        unsigned long nr = f_pos;

        if (nr != f_pos)        /* 32bit overflow? */
                return NULL;

        rcu_read_lock();
        task = pid_task(pid, PIDTYPE_PID);
        if (!task)
                goto fail;

        /* Attempt to start with the tid of a thread */
        if (tid && nr) {
                pos = find_task_by_pid_ns(tid, ns);
                if (pos && same_thread_group(pos, task))
                        goto found;
        }

        /* If nr exceeds the number of threads there is nothing todo */
        if (nr >= get_nr_threads(task))
                goto fail;

        /* If we haven't found our starting place yet start
         * with the leader and walk nr threads forward.
         */
        pos = task = task->group_leader;
        do {
                if (!nr--)
                        goto found;
        } while_each_thread(task, pos);
fail:
        pos = NULL;
        goto out;
found:
        get_task_struct(pos);
out:
        rcu_read_unlock();
        return pos;
}

/*
 * Find the next thread in the thread list.
 * Return NULL if there is an error or no next thread.
 *
 * The reference to the input task_struct is released.
 */
static struct task_struct *next_tid(struct task_struct *start)
{
        struct task_struct *pos = NULL;
        rcu_read_lock();
        if (pid_alive(start)) {
                pos = next_thread(start);
                if (thread_group_leader(pos))
                        pos = NULL;
                else
                        get_task_struct(pos);
        }
        rcu_read_unlock();
        put_task_struct(start);
        return pos;
}

/* for the /proc/TGID/task/ directories */
static int proc_task_readdir(struct file *file, struct dir_context *ctx)
{
        struct inode *inode = file_inode(file);
        struct task_struct *task;
        struct pid_namespace *ns;
        int tid;

        if (proc_inode_is_dead(inode))
                return -ENOENT;

        if (!dir_emit_dots(file, ctx))
                return 0;

        /* f_version caches the tgid value that the last readdir call couldn't
         * return. lseek aka telldir automagically resets f_version to 0.
         */
        ns = proc_pid_ns(inode->i_sb);
        tid = (int)file->f_version;
        file->f_version = 0;
        for (task = first_tid(proc_pid(inode), tid, ctx->pos - 2, ns);
             task;
             task = next_tid(task), ctx->pos++) {
                char name[10 + 1];
                unsigned int len;
                tid = task_pid_nr_ns(task, ns);
                len = snprintf(name, sizeof(name), "%u", tid);
                if (!proc_fill_cache(file, ctx, name, len,
                                proc_task_instantiate, task, NULL)) {
                        /* returning this tgid failed, save it as the first
                         * pid for the next readir call */
                        file->f_version = (u64)tid;
                        put_task_struct(task);
                        break;
                }
        }

        return 0;
}

static int proc_task_getattr(const struct path *path, struct kstat *stat,
                             u32 request_mask, unsigned int query_flags)
{
        struct inode *inode = d_inode(path->dentry);
        struct task_struct *p = get_proc_task(inode);
        generic_fillattr(inode, stat);

        if (p) {
                stat->nlink += get_nr_threads(p);
                put_task_struct(p);
        }

        return 0;
}

static const struct inode_operations proc_task_inode_operations = {
        .lookup         = proc_task_lookup,
        .getattr        = proc_task_getattr,
        .setattr        = proc_setattr,
        .permission     = proc_pid_permission,
};

static const struct file_operations proc_task_operations = {
        .read           = generic_read_dir,
        .iterate_shared = proc_task_readdir,
        .llseek         = generic_file_llseek,
};

void __init set_proc_pid_nlink(void)
{
        nlink_tid = pid_entry_nlink(tid_base_stuff, ARRAY_SIZE(tid_base_stuff));
        nlink_tgid = pid_entry_nlink(tgid_base_stuff, ARRAY_SIZE(tgid_base_stuff));
}