nbd: make sure request completion won't concurrent

[mirror_ubuntu-jammy-kernel.git] / fs / coredump.c

// SPDX-License-Identifier: GPL-2.0
#include <linux/slab.h>
#include <linux/file.h>
#include <linux/fdtable.h>
#include <linux/freezer.h>
#include <linux/mm.h>
#include <linux/stat.h>
#include <linux/fcntl.h>
#include <linux/swap.h>
#include <linux/ctype.h>
#include <linux/string.h>
#include <linux/init.h>
#include <linux/pagemap.h>
#include <linux/perf_event.h>
#include <linux/highmem.h>
#include <linux/spinlock.h>
#include <linux/key.h>
#include <linux/personality.h>
#include <linux/binfmts.h>
#include <linux/coredump.h>
#include <linux/sched/coredump.h>
#include <linux/sched/signal.h>
#include <linux/sched/task_stack.h>
#include <linux/utsname.h>
#include <linux/pid_namespace.h>
#include <linux/module.h>
#include <linux/namei.h>
#include <linux/mount.h>
#include <linux/security.h>
#include <linux/syscalls.h>
#include <linux/tsacct_kern.h>
#include <linux/cn_proc.h>
#include <linux/audit.h>
#include <linux/tracehook.h>
#include <linux/kmod.h>
#include <linux/fsnotify.h>
#include <linux/fs_struct.h>
#include <linux/pipe_fs_i.h>
#include <linux/oom.h>
#include <linux/compat.h>
#include <linux/fs.h>
#include <linux/path.h>
#include <linux/timekeeping.h>
#include <linux/elf.h>

#include <linux/uaccess.h>
#include <asm/mmu_context.h>
#include <asm/tlb.h>
#include <asm/exec.h>

#include <trace/events/task.h>
#include "internal.h"

#include <trace/events/sched.h>

static bool dump_vma_snapshot(struct coredump_params *cprm);
static void free_vma_snapshot(struct coredump_params *cprm);

int core_uses_pid;
unsigned int core_pipe_limit;
char core_pattern[CORENAME_MAX_SIZE] = "core";
static int core_name_size = CORENAME_MAX_SIZE;

struct core_name {
        char *corename;
        int used, size;
};

/* The maximal length of core_pattern is also specified in sysctl.c */

static int expand_corename(struct core_name *cn, int size)
{
        char *corename = krealloc(cn->corename, size, GFP_KERNEL);

        if (!corename)
                return -ENOMEM;

        if (size > core_name_size) /* racy but harmless */
                core_name_size = size;

        cn->size = ksize(corename);
        cn->corename = corename;
        return 0;
}

static __printf(2, 0) int cn_vprintf(struct core_name *cn, const char *fmt,
                                     va_list arg)
{
        int free, need;
        va_list arg_copy;

again:
        free = cn->size - cn->used;

        va_copy(arg_copy, arg);
        need = vsnprintf(cn->corename + cn->used, free, fmt, arg_copy);
        va_end(arg_copy);

        if (need < free) {
                cn->used += need;
                return 0;
        }

        if (!expand_corename(cn, cn->size + need - free + 1))
                goto again;

        return -ENOMEM;
}

static __printf(2, 3) int cn_printf(struct core_name *cn, const char *fmt, ...)
{
        va_list arg;
        int ret;

        va_start(arg, fmt);
        ret = cn_vprintf(cn, fmt, arg);
        va_end(arg);

        return ret;
}

static __printf(2, 3)
int cn_esc_printf(struct core_name *cn, const char *fmt, ...)
{
        int cur = cn->used;
        va_list arg;
        int ret;

        va_start(arg, fmt);
        ret = cn_vprintf(cn, fmt, arg);
        va_end(arg);

        if (ret == 0) {
                /*
                 * Ensure that this coredump name component can't cause the
                 * resulting corefile path to consist of a ".." or ".".
                 */
                if ((cn->used - cur == 1 && cn->corename[cur] == '.') ||
                                (cn->used - cur == 2 && cn->corename[cur] == '.'
                                && cn->corename[cur+1] == '.'))
                        cn->corename[cur] = '!';

                /*
                 * Empty names are fishy and could be used to create a "//" in a
                 * corefile name, causing the coredump to happen one directory
                 * level too high. Enforce that all components of the core
                 * pattern are at least one character long.
                 */
                if (cn->used == cur)
                        ret = cn_printf(cn, "!");
        }

        for (; cur < cn->used; ++cur) {
                if (cn->corename[cur] == '/')
                        cn->corename[cur] = '!';
        }
        return ret;
}

static int cn_print_exe_file(struct core_name *cn, bool name_only)
{
        struct file *exe_file;
        char *pathbuf, *path, *ptr;
        int ret;

        exe_file = get_mm_exe_file(current->mm);
        if (!exe_file)
                return cn_esc_printf(cn, "%s (path unknown)", current->comm);

        pathbuf = kmalloc(PATH_MAX, GFP_KERNEL);
        if (!pathbuf) {
                ret = -ENOMEM;
                goto put_exe_file;
        }

        path = file_path(exe_file, pathbuf, PATH_MAX);
        if (IS_ERR(path)) {
                ret = PTR_ERR(path);
                goto free_buf;
        }

        if (name_only) {
                ptr = strrchr(path, '/');
                if (ptr)
                        path = ptr + 1;
        }
        ret = cn_esc_printf(cn, "%s", path);

free_buf:
        kfree(pathbuf);
put_exe_file:
        fput(exe_file);
        return ret;
}

/* format_corename will inspect the pattern parameter, and output a
 * name into corename, which must have space for at least
 * CORENAME_MAX_SIZE bytes plus one byte for the zero terminator.
 */
static int format_corename(struct core_name *cn, struct coredump_params *cprm,
                           size_t **argv, int *argc)
{
        const struct cred *cred = current_cred();
        const char *pat_ptr = core_pattern;
        int ispipe = (*pat_ptr == '|');
        bool was_space = false;
        int pid_in_pattern = 0;
        int err = 0;

        cn->used = 0;
        cn->corename = NULL;
        if (expand_corename(cn, core_name_size))
                return -ENOMEM;
        cn->corename[0] = '\0';

        if (ispipe) {
                int argvs = sizeof(core_pattern) / 2;
                (*argv) = kmalloc_array(argvs, sizeof(**argv), GFP_KERNEL);
                if (!(*argv))
                        return -ENOMEM;
                (*argv)[(*argc)++] = 0;
                ++pat_ptr;
                if (!(*pat_ptr))
                        return -ENOMEM;
        }

        /* Repeat as long as we have more pattern to process and more output
           space */
        while (*pat_ptr) {
                /*
                 * Split on spaces before doing template expansion so that
                 * %e and %E don't get split if they have spaces in them
                 */
                if (ispipe) {
                        if (isspace(*pat_ptr)) {
                                if (cn->used != 0)
                                        was_space = true;
                                pat_ptr++;
                                continue;
                        } else if (was_space) {
                                was_space = false;
                                err = cn_printf(cn, "%c", '\0');
                                if (err)
                                        return err;
                                (*argv)[(*argc)++] = cn->used;
                        }
                }
                if (*pat_ptr != '%') {
                        err = cn_printf(cn, "%c", *pat_ptr++);
                } else {
                        switch (*++pat_ptr) {
                        /* single % at the end, drop that */
                        case 0:
                                goto out;
                        /* Double percent, output one percent */
                        case '%':
                                err = cn_printf(cn, "%c", '%');
                                break;
                        /* pid */
                        case 'p':
                                pid_in_pattern = 1;
                                err = cn_printf(cn, "%d",
                                              task_tgid_vnr(current));
                                break;
                        /* global pid */
                        case 'P':
                                err = cn_printf(cn, "%d",
                                              task_tgid_nr(current));
                                break;
                        case 'i':
                                err = cn_printf(cn, "%d",
                                              task_pid_vnr(current));
                                break;
                        case 'I':
                                err = cn_printf(cn, "%d",
                                              task_pid_nr(current));
                                break;
                        /* uid */
                        case 'u':
                                err = cn_printf(cn, "%u",
                                                from_kuid(&init_user_ns,
                                                          cred->uid));
                                break;
                        /* gid */
                        case 'g':
                                err = cn_printf(cn, "%u",
                                                from_kgid(&init_user_ns,
                                                          cred->gid));
                                break;
                        case 'd':
                                err = cn_printf(cn, "%d",
                                        __get_dumpable(cprm->mm_flags));
                                break;
                        /* signal that caused the coredump */
                        case 's':
                                err = cn_printf(cn, "%d",
                                                cprm->siginfo->si_signo);
                                break;
                        /* UNIX time of coredump */
                        case 't': {
                                time64_t time;

                                time = ktime_get_real_seconds();
                                err = cn_printf(cn, "%lld", time);
                                break;
                        }
                        /* hostname */
                        case 'h':
                                down_read(&uts_sem);
                                err = cn_esc_printf(cn, "%s",
                                              utsname()->nodename);
                                up_read(&uts_sem);
                                break;
                        /* executable, could be changed by prctl PR_SET_NAME etc */
                        case 'e':
                                err = cn_esc_printf(cn, "%s", current->comm);
                                break;
                        /* file name of executable */
                        case 'f':
                                err = cn_print_exe_file(cn, true);
                                break;
                        case 'E':
                                err = cn_print_exe_file(cn, false);
                                break;
                        /* core limit size */
                        case 'c':
                                err = cn_printf(cn, "%lu",
                                              rlimit(RLIMIT_CORE));
                                break;
                        default:
                                break;
                        }
                        ++pat_ptr;
                }

                if (err)
                        return err;
        }

out:
        /* Backward compatibility with core_uses_pid:
         *
         * If core_pattern does not include a %p (as is the default)
         * and core_uses_pid is set, then .%pid will be appended to
         * the filename. Do not do this for piped commands. */
        if (!ispipe && !pid_in_pattern && core_uses_pid) {
                err = cn_printf(cn, ".%d", task_tgid_vnr(current));
                if (err)
                        return err;
        }
        return ispipe;
}

static int zap_process(struct task_struct *start, int exit_code, int flags)
{
        struct task_struct *t;
        int nr = 0;

        /* ignore all signals except SIGKILL, see prepare_signal() */
        start->signal->flags = SIGNAL_GROUP_COREDUMP | flags;
        start->signal->group_exit_code = exit_code;
        start->signal->group_stop_count = 0;

        for_each_thread(start, t) {
                task_clear_jobctl_pending(t, JOBCTL_PENDING_MASK);
                if (t != current && t->mm) {
                        sigaddset(&t->pending.signal, SIGKILL);
                        signal_wake_up(t, 1);
                        nr++;
                }
        }

        return nr;
}

static int zap_threads(struct task_struct *tsk, struct mm_struct *mm,
                        struct core_state *core_state, int exit_code)
{
        struct task_struct *g, *p;
        unsigned long flags;
        int nr = -EAGAIN;

        spin_lock_irq(&tsk->sighand->siglock);
        if (!signal_group_exit(tsk->signal)) {
                mm->core_state = core_state;
                tsk->signal->group_exit_task = tsk;
                nr = zap_process(tsk, exit_code, 0);
                clear_tsk_thread_flag(tsk, TIF_SIGPENDING);
        }
        spin_unlock_irq(&tsk->sighand->siglock);
        if (unlikely(nr < 0))
                return nr;

        tsk->flags |= PF_DUMPCORE;
        if (atomic_read(&mm->mm_users) == nr + 1)
                goto done;
        /*
         * We should find and kill all tasks which use this mm, and we should
         * count them correctly into ->nr_threads. We don't take tasklist
         * lock, but this is safe wrt:
         *
         * fork:
         *      None of sub-threads can fork after zap_process(leader). All
         *      processes which were created before this point should be
         *      visible to zap_threads() because copy_process() adds the new
         *      process to the tail of init_task.tasks list, and lock/unlock
         *      of ->siglock provides a memory barrier.
         *
         * do_exit:
         *      The caller holds mm->mmap_lock. This means that the task which
         *      uses this mm can't pass exit_mm(), so it can't exit or clear
         *      its ->mm.
         *
         * de_thread:
         *      It does list_replace_rcu(&leader->tasks, &current->tasks),
         *      we must see either old or new leader, this does not matter.
         *      However, it can change p->sighand, so lock_task_sighand(p)
         *      must be used. Since p->mm != NULL and we hold ->mmap_lock
         *      it can't fail.
         *
         *      Note also that "g" can be the old leader with ->mm == NULL
         *      and already unhashed and thus removed from ->thread_group.
         *      This is OK, __unhash_process()->list_del_rcu() does not
         *      clear the ->next pointer, we will find the new leader via
         *      next_thread().
         */
        rcu_read_lock();
        for_each_process(g) {
                if (g == tsk->group_leader)
                        continue;
                if (g->flags & PF_KTHREAD)
                        continue;

                for_each_thread(g, p) {
                        if (unlikely(!p->mm))
                                continue;
                        if (unlikely(p->mm == mm)) {
                                lock_task_sighand(p, &flags);
                                nr += zap_process(p, exit_code,
                                                        SIGNAL_GROUP_EXIT);
                                unlock_task_sighand(p, &flags);
                        }
                        break;
                }
        }
        rcu_read_unlock();
done:
        atomic_set(&core_state->nr_threads, nr);
        return nr;
}

static int coredump_wait(int exit_code, struct core_state *core_state)
{
        struct task_struct *tsk = current;
        struct mm_struct *mm = tsk->mm;
        int core_waiters = -EBUSY;

        init_completion(&core_state->startup);
        core_state->dumper.task = tsk;
        core_state->dumper.next = NULL;

        if (mmap_write_lock_killable(mm))
                return -EINTR;

        if (!mm->core_state)
                core_waiters = zap_threads(tsk, mm, core_state, exit_code);
        mmap_write_unlock(mm);

        if (core_waiters > 0) {
                struct core_thread *ptr;

                freezer_do_not_count();
                wait_for_completion(&core_state->startup);
                freezer_count();
                /*
                 * Wait for all the threads to become inactive, so that
                 * all the thread context (extended register state, like
                 * fpu etc) gets copied to the memory.
                 */
                ptr = core_state->dumper.next;
                while (ptr != NULL) {
                        wait_task_inactive(ptr->task, 0);
                        ptr = ptr->next;
                }
        }

        return core_waiters;
}

static void coredump_finish(struct mm_struct *mm, bool core_dumped)
{
        struct core_thread *curr, *next;
        struct task_struct *task;

        spin_lock_irq(&current->sighand->siglock);
        if (core_dumped && !__fatal_signal_pending(current))
                current->signal->group_exit_code |= 0x80;
        current->signal->group_exit_task = NULL;
        current->signal->flags = SIGNAL_GROUP_EXIT;
        spin_unlock_irq(&current->sighand->siglock);

        next = mm->core_state->dumper.next;
        while ((curr = next) != NULL) {
                next = curr->next;
                task = curr->task;
                /*
                 * see exit_mm(), curr->task must not see
                 * ->task == NULL before we read ->next.
                 */
                smp_mb();
                curr->task = NULL;
                wake_up_process(task);
        }

        mm->core_state = NULL;
}

static bool dump_interrupted(void)
{
        /*
         * SIGKILL or freezing() interrupt the coredumping. Perhaps we
         * can do try_to_freeze() and check __fatal_signal_pending(),
         * but then we need to teach dump_write() to restart and clear
         * TIF_SIGPENDING.
         */
        return fatal_signal_pending(current) || freezing(current);
}

static void wait_for_dump_helpers(struct file *file)
{
        struct pipe_inode_info *pipe = file->private_data;

        pipe_lock(pipe);
        pipe->readers++;
        pipe->writers--;
        wake_up_interruptible_sync(&pipe->rd_wait);
        kill_fasync(&pipe->fasync_readers, SIGIO, POLL_IN);
        pipe_unlock(pipe);

        /*
         * We actually want wait_event_freezable() but then we need
         * to clear TIF_SIGPENDING and improve dump_interrupted().
         */
        wait_event_interruptible(pipe->rd_wait, pipe->readers == 1);

        pipe_lock(pipe);
        pipe->readers--;
        pipe->writers++;
        pipe_unlock(pipe);
}

/*
 * umh_pipe_setup
 * helper function to customize the process used
 * to collect the core in userspace.  Specifically
 * it sets up a pipe and installs it as fd 0 (stdin)
 * for the process.  Returns 0 on success, or
 * PTR_ERR on failure.
 * Note that it also sets the core limit to 1.  This
 * is a special value that we use to trap recursive
 * core dumps
 */
static int umh_pipe_setup(struct subprocess_info *info, struct cred *new)
{
        struct file *files[2];
        struct coredump_params *cp = (struct coredump_params *)info->data;
        int err = create_pipe_files(files, 0);
        if (err)
                return err;

        cp->file = files[1];

        err = replace_fd(0, files[0], 0);
        fput(files[0]);
        /* and disallow core files too */
        current->signal->rlim[RLIMIT_CORE] = (struct rlimit){1, 1};

        return err;
}

void do_coredump(const kernel_siginfo_t *siginfo)
{
        struct core_state core_state;
        struct core_name cn;
        struct mm_struct *mm = current->mm;
        struct linux_binfmt * binfmt;
        const struct cred *old_cred;
        struct cred *cred;
        int retval = 0;
        int ispipe;
        size_t *argv = NULL;
        int argc = 0;
        /* require nonrelative corefile path and be extra careful */
        bool need_suid_safe = false;
        bool core_dumped = false;
        static atomic_t core_dump_count = ATOMIC_INIT(0);
        struct coredump_params cprm = {
                .siginfo = siginfo,
                .regs = signal_pt_regs(),
                .limit = rlimit(RLIMIT_CORE),
                /*
                 * We must use the same mm->flags while dumping core to avoid
                 * inconsistency of bit flags, since this flag is not protected
                 * by any locks.
                 */
                .mm_flags = mm->flags,
                .vma_meta = NULL,
        };

        audit_core_dumps(siginfo->si_signo);

        binfmt = mm->binfmt;
        if (!binfmt || !binfmt->core_dump)
                goto fail;
        if (!__get_dumpable(cprm.mm_flags))
                goto fail;

        cred = prepare_creds();
        if (!cred)
                goto fail;
        /*
         * We cannot trust fsuid as being the "true" uid of the process
         * nor do we know its entire history. We only know it was tainted
         * so we dump it as root in mode 2, and only into a controlled
         * environment (pipe handler or fully qualified path).
         */
        if (__get_dumpable(cprm.mm_flags) == SUID_DUMP_ROOT) {
                /* Setuid core dump mode */
                cred->fsuid = GLOBAL_ROOT_UID;  /* Dump root private */
                need_suid_safe = true;
        }

        retval = coredump_wait(siginfo->si_signo, &core_state);
        if (retval < 0)
                goto fail_creds;

        old_cred = override_creds(cred);

        ispipe = format_corename(&cn, &cprm, &argv, &argc);

        if (ispipe) {
                int argi;
                int dump_count;
                char **helper_argv;
                struct subprocess_info *sub_info;

                if (ispipe < 0) {
                        printk(KERN_WARNING "format_corename failed\n");
                        printk(KERN_WARNING "Aborting core\n");
                        goto fail_unlock;
                }

                if (cprm.limit == 1) {
                        /* See umh_pipe_setup() which sets RLIMIT_CORE = 1.
                         *
                         * Normally core limits are irrelevant to pipes, since
                         * we're not writing to the file system, but we use
                         * cprm.limit of 1 here as a special value, this is a
                         * consistent way to catch recursive crashes.
                         * We can still crash if the core_pattern binary sets
                         * RLIM_CORE = !1, but it runs as root, and can do
                         * lots of stupid things.
                         *
                         * Note that we use task_tgid_vnr here to grab the pid
                         * of the process group leader.  That way we get the
                         * right pid if a thread in a multi-threaded
                         * core_pattern process dies.
                         */
                        printk(KERN_WARNING
                                "Process %d(%s) has RLIMIT_CORE set to 1\n",
                                task_tgid_vnr(current), current->comm);
                        printk(KERN_WARNING "Aborting core\n");
                        goto fail_unlock;
                }
                cprm.limit = RLIM_INFINITY;

                dump_count = atomic_inc_return(&core_dump_count);
                if (core_pipe_limit && (core_pipe_limit < dump_count)) {
                        printk(KERN_WARNING "Pid %d(%s) over core_pipe_limit\n",
                               task_tgid_vnr(current), current->comm);
                        printk(KERN_WARNING "Skipping core dump\n");
                        goto fail_dropcount;
                }

                helper_argv = kmalloc_array(argc + 1, sizeof(*helper_argv),
                                            GFP_KERNEL);
                if (!helper_argv) {
                        printk(KERN_WARNING "%s failed to allocate memory\n",
                               __func__);
                        goto fail_dropcount;
                }
                for (argi = 0; argi < argc; argi++)
                        helper_argv[argi] = cn.corename + argv[argi];
                helper_argv[argi] = NULL;

                retval = -ENOMEM;
                sub_info = call_usermodehelper_setup(helper_argv[0],
                                                helper_argv, NULL, GFP_KERNEL,
                                                umh_pipe_setup, NULL, &cprm);
                if (sub_info)
                        retval = call_usermodehelper_exec(sub_info,
                                                          UMH_WAIT_EXEC);

                kfree(helper_argv);
                if (retval) {
                        printk(KERN_INFO "Core dump to |%s pipe failed\n",
                               cn.corename);
                        goto close_fail;
                }
        } else {
                struct user_namespace *mnt_userns;
                struct inode *inode;
                int open_flags = O_CREAT | O_RDWR | O_NOFOLLOW |
                                 O_LARGEFILE | O_EXCL;

                if (cprm.limit < binfmt->min_coredump)
                        goto fail_unlock;

                if (need_suid_safe && cn.corename[0] != '/') {
                        printk(KERN_WARNING "Pid %d(%s) can only dump core "\
                                "to fully qualified path!\n",
                                task_tgid_vnr(current), current->comm);
                        printk(KERN_WARNING "Skipping core dump\n");
                        goto fail_unlock;
                }

                /*
                 * Unlink the file if it exists unless this is a SUID
                 * binary - in that case, we're running around with root
                 * privs and don't want to unlink another user's coredump.
                 */
                if (!need_suid_safe) {
                        /*
                         * If it doesn't exist, that's fine. If there's some
                         * other problem, we'll catch it at the filp_open().
                         */
                        do_unlinkat(AT_FDCWD, getname_kernel(cn.corename));
                }

                /*
                 * There is a race between unlinking and creating the
                 * file, but if that causes an EEXIST here, that's
                 * fine - another process raced with us while creating
                 * the corefile, and the other process won. To userspace,
                 * what matters is that at least one of the two processes
                 * writes its coredump successfully, not which one.
                 */
                if (need_suid_safe) {
                        /*
                         * Using user namespaces, normal user tasks can change
                         * their current->fs->root to point to arbitrary
                         * directories. Since the intention of the "only dump
                         * with a fully qualified path" rule is to control where
                         * coredumps may be placed using root privileges,
                         * current->fs->root must not be used. Instead, use the
                         * root directory of init_task.
                         */
                        struct path root;

                        task_lock(&init_task);
                        get_fs_root(init_task.fs, &root);
                        task_unlock(&init_task);
                        cprm.file = file_open_root(&root, cn.corename,
                                                   open_flags, 0600);
                        path_put(&root);
                } else {
                        cprm.file = filp_open(cn.corename, open_flags, 0600);
                }
                if (IS_ERR(cprm.file))
                        goto fail_unlock;

                inode = file_inode(cprm.file);
                if (inode->i_nlink > 1)
                        goto close_fail;
                if (d_unhashed(cprm.file->f_path.dentry))
                        goto close_fail;
                /*
                 * AK: actually i see no reason to not allow this for named
                 * pipes etc, but keep the previous behaviour for now.
                 */
                if (!S_ISREG(inode->i_mode))
                        goto close_fail;
                /*
                 * Don't dump core if the filesystem changed owner or mode
                 * of the file during file creation. This is an issue when
                 * a process dumps core while its cwd is e.g. on a vfat
                 * filesystem.
                 */
                mnt_userns = file_mnt_user_ns(cprm.file);
                if (!uid_eq(i_uid_into_mnt(mnt_userns, inode),
                            current_fsuid())) {
                        pr_info_ratelimited("Core dump to %s aborted: cannot preserve file owner\n",
                                            cn.corename);
                        goto close_fail;
                }
                if ((inode->i_mode & 0677) != 0600) {
                        pr_info_ratelimited("Core dump to %s aborted: cannot preserve file permissions\n",
                                            cn.corename);
                        goto close_fail;
                }
                if (!(cprm.file->f_mode & FMODE_CAN_WRITE))
                        goto close_fail;
                if (do_truncate(mnt_userns, cprm.file->f_path.dentry,
                                0, 0, cprm.file))
                        goto close_fail;
        }

        /* get us an unshared descriptor table; almost always a no-op */
        /* The cell spufs coredump code reads the file descriptor tables */
        retval = unshare_files();
        if (retval)
                goto close_fail;
        if (!dump_interrupted()) {
                /*
                 * umh disabled with CONFIG_STATIC_USERMODEHELPER_PATH="" would
                 * have this set to NULL.
                 */
                if (!cprm.file) {
                        pr_info("Core dump to |%s disabled\n", cn.corename);
                        goto close_fail;
                }
                if (!dump_vma_snapshot(&cprm))
                        goto close_fail;

                file_start_write(cprm.file);
                core_dumped = binfmt->core_dump(&cprm);
                /*
                 * Ensures that file size is big enough to contain the current
                 * file postion. This prevents gdb from complaining about
                 * a truncated file if the last "write" to the file was
                 * dump_skip.
                 */
                if (cprm.to_skip) {
                        cprm.to_skip--;
                        dump_emit(&cprm, "", 1);
                }
                file_end_write(cprm.file);
                free_vma_snapshot(&cprm);
        }
        if (ispipe && core_pipe_limit)
                wait_for_dump_helpers(cprm.file);
close_fail:
        if (cprm.file)
                filp_close(cprm.file, NULL);
fail_dropcount:
        if (ispipe)
                atomic_dec(&core_dump_count);
fail_unlock:
        kfree(argv);
        kfree(cn.corename);
        coredump_finish(mm, core_dumped);
        revert_creds(old_cred);
fail_creds:
        put_cred(cred);
fail:
        return;
}

/*
 * Core dumping helper functions.  These are the only things you should
 * do on a core-file: use only these functions to write out all the
 * necessary info.
 */
static int __dump_emit(struct coredump_params *cprm, const void *addr, int nr)
{
        struct file *file = cprm->file;
        loff_t pos = file->f_pos;
        ssize_t n;
        if (cprm->written + nr > cprm->limit)
                return 0;


        if (dump_interrupted())
                return 0;
        n = __kernel_write(file, addr, nr, &pos);
        if (n != nr)
                return 0;
        file->f_pos = pos;
        cprm->written += n;
        cprm->pos += n;

        return 1;
}

static int __dump_skip(struct coredump_params *cprm, size_t nr)
{
        static char zeroes[PAGE_SIZE];
        struct file *file = cprm->file;
        if (file->f_op->llseek && file->f_op->llseek != no_llseek) {
                if (dump_interrupted() ||
                    file->f_op->llseek(file, nr, SEEK_CUR) < 0)
                        return 0;
                cprm->pos += nr;
                return 1;
        } else {
                while (nr > PAGE_SIZE) {
                        if (!__dump_emit(cprm, zeroes, PAGE_SIZE))
                                return 0;
                        nr -= PAGE_SIZE;
                }
                return __dump_emit(cprm, zeroes, nr);
        }
}

int dump_emit(struct coredump_params *cprm, const void *addr, int nr)
{
        if (cprm->to_skip) {
                if (!__dump_skip(cprm, cprm->to_skip))
                        return 0;
                cprm->to_skip = 0;
        }
        return __dump_emit(cprm, addr, nr);
}
EXPORT_SYMBOL(dump_emit);

void dump_skip_to(struct coredump_params *cprm, unsigned long pos)
{
        cprm->to_skip = pos - cprm->pos;
}
EXPORT_SYMBOL(dump_skip_to);

void dump_skip(struct coredump_params *cprm, size_t nr)
{
        cprm->to_skip += nr;
}
EXPORT_SYMBOL(dump_skip);

#ifdef CONFIG_ELF_CORE
int dump_user_range(struct coredump_params *cprm, unsigned long start,
                    unsigned long len)
{
        unsigned long addr;

        for (addr = start; addr < start + len; addr += PAGE_SIZE) {
                struct page *page;
                int stop;

                /*
                 * To avoid having to allocate page tables for virtual address
                 * ranges that have never been used yet, and also to make it
                 * easy to generate sparse core files, use a helper that returns
                 * NULL when encountering an empty page table entry that would
                 * otherwise have been filled with the zero page.
                 */
                page = get_dump_page(addr);
                if (page) {
                        void *kaddr = kmap_local_page(page);

                        stop = !dump_emit(cprm, kaddr, PAGE_SIZE);
                        kunmap_local(kaddr);
                        put_page(page);
                        if (stop)
                                return 0;
                } else {
                        dump_skip(cprm, PAGE_SIZE);
                }
        }
        return 1;
}
#endif

int dump_align(struct coredump_params *cprm, int align)
{
        unsigned mod = (cprm->pos + cprm->to_skip) & (align - 1);
        if (align & (align - 1))
                return 0;
        if (mod)
                cprm->to_skip += align - mod;
        return 1;
}
EXPORT_SYMBOL(dump_align);

/*
 * The purpose of always_dump_vma() is to make sure that special kernel mappings
 * that are useful for post-mortem analysis are included in every core dump.
 * In that way we ensure that the core dump is fully interpretable later
 * without matching up the same kernel and hardware config to see what PC values
 * meant. These special mappings include - vDSO, vsyscall, and other
 * architecture specific mappings
 */
static bool always_dump_vma(struct vm_area_struct *vma)
{
        /* Any vsyscall mappings? */
        if (vma == get_gate_vma(vma->vm_mm))
                return true;

        /*
         * Assume that all vmas with a .name op should always be dumped.
         * If this changes, a new vm_ops field can easily be added.
         */
        if (vma->vm_ops && vma->vm_ops->name && vma->vm_ops->name(vma))
                return true;

        /*
         * arch_vma_name() returns non-NULL for special architecture mappings,
         * such as vDSO sections.
         */
        if (arch_vma_name(vma))
                return true;

        return false;
}

#define DUMP_SIZE_MAYBE_ELFHDR_PLACEHOLDER 1

/*
 * Decide how much of @vma's contents should be included in a core dump.
 */
static unsigned long vma_dump_size(struct vm_area_struct *vma,
                                   unsigned long mm_flags)
{
#define FILTER(type)    (mm_flags & (1UL << MMF_DUMP_##type))

        /* always dump the vdso and vsyscall sections */
        if (always_dump_vma(vma))
                goto whole;

        if (vma->vm_flags & VM_DONTDUMP)
                return 0;

        /* support for DAX */
        if (vma_is_dax(vma)) {
                if ((vma->vm_flags & VM_SHARED) && FILTER(DAX_SHARED))
                        goto whole;
                if (!(vma->vm_flags & VM_SHARED) && FILTER(DAX_PRIVATE))
                        goto whole;
                return 0;
        }

        /* Hugetlb memory check */
        if (is_vm_hugetlb_page(vma)) {
                if ((vma->vm_flags & VM_SHARED) && FILTER(HUGETLB_SHARED))
                        goto whole;
                if (!(vma->vm_flags & VM_SHARED) && FILTER(HUGETLB_PRIVATE))
                        goto whole;
                return 0;
        }

        /* Do not dump I/O mapped devices or special mappings */
        if (vma->vm_flags & VM_IO)
                return 0;

        /* By default, dump shared memory if mapped from an anonymous file. */
        if (vma->vm_flags & VM_SHARED) {
                if (file_inode(vma->vm_file)->i_nlink == 0 ?
                    FILTER(ANON_SHARED) : FILTER(MAPPED_SHARED))
                        goto whole;
                return 0;
        }

        /* Dump segments that have been written to.  */
        if ((!IS_ENABLED(CONFIG_MMU) || vma->anon_vma) && FILTER(ANON_PRIVATE))
                goto whole;
        if (vma->vm_file == NULL)
                return 0;

        if (FILTER(MAPPED_PRIVATE))
                goto whole;

        /*
         * If this is the beginning of an executable file mapping,
         * dump the first page to aid in determining what was mapped here.
         */
        if (FILTER(ELF_HEADERS) &&
            vma->vm_pgoff == 0 && (vma->vm_flags & VM_READ)) {
                if ((READ_ONCE(file_inode(vma->vm_file)->i_mode) & 0111) != 0)
                        return PAGE_SIZE;

                /*
                 * ELF libraries aren't always executable.
                 * We'll want to check whether the mapping starts with the ELF
                 * magic, but not now - we're holding the mmap lock,
                 * so copy_from_user() doesn't work here.
                 * Use a placeholder instead, and fix it up later in
                 * dump_vma_snapshot().
                 */
                return DUMP_SIZE_MAYBE_ELFHDR_PLACEHOLDER;
        }

#undef  FILTER

        return 0;

whole:
        return vma->vm_end - vma->vm_start;
}

static struct vm_area_struct *first_vma(struct task_struct *tsk,
                                        struct vm_area_struct *gate_vma)
{
        struct vm_area_struct *ret = tsk->mm->mmap;

        if (ret)
                return ret;
        return gate_vma;
}

/*
 * Helper function for iterating across a vma list.  It ensures that the caller
 * will visit `gate_vma' prior to terminating the search.
 */
static struct vm_area_struct *next_vma(struct vm_area_struct *this_vma,
                                       struct vm_area_struct *gate_vma)
{
        struct vm_area_struct *ret;

        ret = this_vma->vm_next;
        if (ret)
                return ret;
        if (this_vma == gate_vma)
                return NULL;
        return gate_vma;
}

static void free_vma_snapshot(struct coredump_params *cprm)
{
        if (cprm->vma_meta) {
                int i;
                for (i = 0; i < cprm->vma_count; i++) {
                        struct file *file = cprm->vma_meta[i].file;
                        if (file)
                                fput(file);
                }
                kvfree(cprm->vma_meta);
                cprm->vma_meta = NULL;
        }
}

/*
 * Under the mmap_lock, take a snapshot of relevant information about the task's
 * VMAs.
 */
static bool dump_vma_snapshot(struct coredump_params *cprm)
{
        struct vm_area_struct *vma, *gate_vma;
        struct mm_struct *mm = current->mm;
        int i;

        /*
         * Once the stack expansion code is fixed to not change VMA bounds
         * under mmap_lock in read mode, this can be changed to take the
         * mmap_lock in read mode.
         */
        if (mmap_write_lock_killable(mm))
                return false;

        cprm->vma_data_size = 0;
        gate_vma = get_gate_vma(mm);
        cprm->vma_count = mm->map_count + (gate_vma ? 1 : 0);

        cprm->vma_meta = kvmalloc_array(cprm->vma_count, sizeof(*cprm->vma_meta), GFP_KERNEL);
        if (!cprm->vma_meta) {
                mmap_write_unlock(mm);
                return false;
        }

        for (i = 0, vma = first_vma(current, gate_vma); vma != NULL;
                        vma = next_vma(vma, gate_vma), i++) {
                struct core_vma_metadata *m = cprm->vma_meta + i;

                m->start = vma->vm_start;
                m->end = vma->vm_end;
                m->flags = vma->vm_flags;
                m->dump_size = vma_dump_size(vma, cprm->mm_flags);
                m->pgoff = vma->vm_pgoff;

                m->file = vma->vm_file;
                if (m->file)
                        get_file(m->file);
        }

        mmap_write_unlock(mm);

        for (i = 0; i < cprm->vma_count; i++) {
                struct core_vma_metadata *m = cprm->vma_meta + i;

                if (m->dump_size == DUMP_SIZE_MAYBE_ELFHDR_PLACEHOLDER) {
                        char elfmag[SELFMAG];

                        if (copy_from_user(elfmag, (void __user *)m->start, SELFMAG) ||
                                        memcmp(elfmag, ELFMAG, SELFMAG) != 0) {
                                m->dump_size = 0;
                        } else {
                                m->dump_size = PAGE_SIZE;
                        }
                }

                cprm->vma_data_size += m->dump_size;
        }

        return true;
}