cgroup-v1: Require capabilities to set release_agent

[mirror_ubuntu-focal-kernel.git] / kernel / cgroup / cgroup-v1.c

// SPDX-License-Identifier: GPL-2.0-only
#include "cgroup-internal.h"

#include <linux/ctype.h>
#include <linux/kmod.h>
#include <linux/sort.h>
#include <linux/delay.h>
#include <linux/mm.h>
#include <linux/sched/signal.h>
#include <linux/sched/task.h>
#include <linux/magic.h>
#include <linux/slab.h>
#include <linux/vmalloc.h>
#include <linux/delayacct.h>
#include <linux/pid_namespace.h>
#include <linux/cgroupstats.h>
#include <linux/fs_parser.h>

#include <trace/events/cgroup.h>

#define cg_invalf(fc, fmt, ...) invalf(fc, fmt, ## __VA_ARGS__)

/*
 * pidlists linger the following amount before being destroyed.  The goal
 * is avoiding frequent destruction in the middle of consecutive read calls
 * Expiring in the middle is a performance problem not a correctness one.
 * 1 sec should be enough.
 */
#define CGROUP_PIDLIST_DESTROY_DELAY    HZ

/* Controllers blocked by the commandline in v1 */
static u16 cgroup_no_v1_mask;

/* disable named v1 mounts */
static bool cgroup_no_v1_named;

/*
 * pidlist destructions need to be flushed on cgroup destruction.  Use a
 * separate workqueue as flush domain.
 */
static struct workqueue_struct *cgroup_pidlist_destroy_wq;

/*
 * Protects cgroup_subsys->release_agent_path.  Modifying it also requires
 * cgroup_mutex.  Reading requires either cgroup_mutex or this spinlock.
 */
static DEFINE_SPINLOCK(release_agent_path_lock);

bool cgroup1_ssid_disabled(int ssid)
{
        return cgroup_no_v1_mask & (1 << ssid);
}

/**
 * cgroup_attach_task_all - attach task 'tsk' to all cgroups of task 'from'
 * @from: attach to all cgroups of a given task
 * @tsk: the task to be attached
 */
int cgroup_attach_task_all(struct task_struct *from, struct task_struct *tsk)
{
        struct cgroup_root *root;
        int retval = 0;

        mutex_lock(&cgroup_mutex);
        percpu_down_write(&cgroup_threadgroup_rwsem);
        for_each_root(root) {
                struct cgroup *from_cgrp;

                if (root == &cgrp_dfl_root)
                        continue;

                spin_lock_irq(&css_set_lock);
                from_cgrp = task_cgroup_from_root(from, root);
                spin_unlock_irq(&css_set_lock);

                retval = cgroup_attach_task(from_cgrp, tsk, false);
                if (retval)
                        break;
        }
        percpu_up_write(&cgroup_threadgroup_rwsem);
        mutex_unlock(&cgroup_mutex);

        return retval;
}
EXPORT_SYMBOL_GPL(cgroup_attach_task_all);

/**
 * cgroup_trasnsfer_tasks - move tasks from one cgroup to another
 * @to: cgroup to which the tasks will be moved
 * @from: cgroup in which the tasks currently reside
 *
 * Locking rules between cgroup_post_fork() and the migration path
 * guarantee that, if a task is forking while being migrated, the new child
 * is guaranteed to be either visible in the source cgroup after the
 * parent's migration is complete or put into the target cgroup.  No task
 * can slip out of migration through forking.
 */
int cgroup_transfer_tasks(struct cgroup *to, struct cgroup *from)
{
        DEFINE_CGROUP_MGCTX(mgctx);
        struct cgrp_cset_link *link;
        struct css_task_iter it;
        struct task_struct *task;
        int ret;

        if (cgroup_on_dfl(to))
                return -EINVAL;

        ret = cgroup_migrate_vet_dst(to);
        if (ret)
                return ret;

        mutex_lock(&cgroup_mutex);

        percpu_down_write(&cgroup_threadgroup_rwsem);

        /* all tasks in @from are being moved, all csets are source */
        spin_lock_irq(&css_set_lock);
        list_for_each_entry(link, &from->cset_links, cset_link)
                cgroup_migrate_add_src(link->cset, to, &mgctx);
        spin_unlock_irq(&css_set_lock);

        ret = cgroup_migrate_prepare_dst(&mgctx);
        if (ret)
                goto out_err;

        /*
         * Migrate tasks one-by-one until @from is empty.  This fails iff
         * ->can_attach() fails.
         */
        do {
                css_task_iter_start(&from->self, 0, &it);

                do {
                        task = css_task_iter_next(&it);
                } while (task && (task->flags & PF_EXITING));

                if (task)
                        get_task_struct(task);
                css_task_iter_end(&it);

                if (task) {
                        ret = cgroup_migrate(task, false, &mgctx);
                        if (!ret)
                                TRACE_CGROUP_PATH(transfer_tasks, to, task, false);
                        put_task_struct(task);
                }
        } while (task && !ret);
out_err:
        cgroup_migrate_finish(&mgctx);
        percpu_up_write(&cgroup_threadgroup_rwsem);
        mutex_unlock(&cgroup_mutex);
        return ret;
}

/*
 * Stuff for reading the 'tasks'/'procs' files.
 *
 * Reading this file can return large amounts of data if a cgroup has
 * *lots* of attached tasks. So it may need several calls to read(),
 * but we cannot guarantee that the information we produce is correct
 * unless we produce it entirely atomically.
 *
 */

/* which pidlist file are we talking about? */
enum cgroup_filetype {
        CGROUP_FILE_PROCS,
        CGROUP_FILE_TASKS,
};

/*
 * A pidlist is a list of pids that virtually represents the contents of one
 * of the cgroup files ("procs" or "tasks"). We keep a list of such pidlists,
 * a pair (one each for procs, tasks) for each pid namespace that's relevant
 * to the cgroup.
 */
struct cgroup_pidlist {
        /*
         * used to find which pidlist is wanted. doesn't change as long as
         * this particular list stays in the list.
        */
        struct { enum cgroup_filetype type; struct pid_namespace *ns; } key;
        /* array of xids */
        pid_t *list;
        /* how many elements the above list has */
        int length;
        /* each of these stored in a list by its cgroup */
        struct list_head links;
        /* pointer to the cgroup we belong to, for list removal purposes */
        struct cgroup *owner;
        /* for delayed destruction */
        struct delayed_work destroy_dwork;
};

/*
 * Used to destroy all pidlists lingering waiting for destroy timer.  None
 * should be left afterwards.
 */
void cgroup1_pidlist_destroy_all(struct cgroup *cgrp)
{
        struct cgroup_pidlist *l, *tmp_l;

        mutex_lock(&cgrp->pidlist_mutex);
        list_for_each_entry_safe(l, tmp_l, &cgrp->pidlists, links)
                mod_delayed_work(cgroup_pidlist_destroy_wq, &l->destroy_dwork, 0);
        mutex_unlock(&cgrp->pidlist_mutex);

        flush_workqueue(cgroup_pidlist_destroy_wq);
        BUG_ON(!list_empty(&cgrp->pidlists));
}

static void cgroup_pidlist_destroy_work_fn(struct work_struct *work)
{
        struct delayed_work *dwork = to_delayed_work(work);
        struct cgroup_pidlist *l = container_of(dwork, struct cgroup_pidlist,
                                                destroy_dwork);
        struct cgroup_pidlist *tofree = NULL;

        mutex_lock(&l->owner->pidlist_mutex);

        /*
         * Destroy iff we didn't get queued again.  The state won't change
         * as destroy_dwork can only be queued while locked.
         */
        if (!delayed_work_pending(dwork)) {
                list_del(&l->links);
                kvfree(l->list);
                put_pid_ns(l->key.ns);
                tofree = l;
        }

        mutex_unlock(&l->owner->pidlist_mutex);
        kfree(tofree);
}

/*
 * pidlist_uniq - given a kmalloc()ed list, strip out all duplicate entries
 * Returns the number of unique elements.
 */
static int pidlist_uniq(pid_t *list, int length)
{
        int src, dest = 1;

        /*
         * we presume the 0th element is unique, so i starts at 1. trivial
         * edge cases first; no work needs to be done for either
         */
        if (length == 0 || length == 1)
                return length;
        /* src and dest walk down the list; dest counts unique elements */
        for (src = 1; src < length; src++) {
                /* find next unique element */
                while (list[src] == list[src-1]) {
                        src++;
                        if (src == length)
                                goto after;
                }
                /* dest always points to where the next unique element goes */
                list[dest] = list[src];
                dest++;
        }
after:
        return dest;
}

/*
 * The two pid files - task and cgroup.procs - guaranteed that the result
 * is sorted, which forced this whole pidlist fiasco.  As pid order is
 * different per namespace, each namespace needs differently sorted list,
 * making it impossible to use, for example, single rbtree of member tasks
 * sorted by task pointer.  As pidlists can be fairly large, allocating one
 * per open file is dangerous, so cgroup had to implement shared pool of
 * pidlists keyed by cgroup and namespace.
 */
static int cmppid(const void *a, const void *b)
{
        return *(pid_t *)a - *(pid_t *)b;
}

static struct cgroup_pidlist *cgroup_pidlist_find(struct cgroup *cgrp,
                                                  enum cgroup_filetype type)
{
        struct cgroup_pidlist *l;
        /* don't need task_nsproxy() if we're looking at ourself */
        struct pid_namespace *ns = task_active_pid_ns(current);

        lockdep_assert_held(&cgrp->pidlist_mutex);

        list_for_each_entry(l, &cgrp->pidlists, links)
                if (l->key.type == type && l->key.ns == ns)
                        return l;
        return NULL;
}

/*
 * find the appropriate pidlist for our purpose (given procs vs tasks)
 * returns with the lock on that pidlist already held, and takes care
 * of the use count, or returns NULL with no locks held if we're out of
 * memory.
 */
static struct cgroup_pidlist *cgroup_pidlist_find_create(struct cgroup *cgrp,
                                                enum cgroup_filetype type)
{
        struct cgroup_pidlist *l;

        lockdep_assert_held(&cgrp->pidlist_mutex);

        l = cgroup_pidlist_find(cgrp, type);
        if (l)
                return l;

        /* entry not found; create a new one */
        l = kzalloc(sizeof(struct cgroup_pidlist), GFP_KERNEL);
        if (!l)
                return l;

        INIT_DELAYED_WORK(&l->destroy_dwork, cgroup_pidlist_destroy_work_fn);
        l->key.type = type;
        /* don't need task_nsproxy() if we're looking at ourself */
        l->key.ns = get_pid_ns(task_active_pid_ns(current));
        l->owner = cgrp;
        list_add(&l->links, &cgrp->pidlists);
        return l;
}

/*
 * Load a cgroup's pidarray with either procs' tgids or tasks' pids
 */
static int pidlist_array_load(struct cgroup *cgrp, enum cgroup_filetype type,
                              struct cgroup_pidlist **lp)
{
        pid_t *array;
        int length;
        int pid, n = 0; /* used for populating the array */
        struct css_task_iter it;
        struct task_struct *tsk;
        struct cgroup_pidlist *l;

        lockdep_assert_held(&cgrp->pidlist_mutex);

        /*
         * If cgroup gets more users after we read count, we won't have
         * enough space - tough.  This race is indistinguishable to the
         * caller from the case that the additional cgroup users didn't
         * show up until sometime later on.
         */
        length = cgroup_task_count(cgrp);
        array = kvmalloc_array(length, sizeof(pid_t), GFP_KERNEL);
        if (!array)
                return -ENOMEM;
        /* now, populate the array */
        css_task_iter_start(&cgrp->self, 0, &it);
        while ((tsk = css_task_iter_next(&it))) {
                if (unlikely(n == length))
                        break;
                /* get tgid or pid for procs or tasks file respectively */
                if (type == CGROUP_FILE_PROCS)
                        pid = task_tgid_vnr(tsk);
                else
                        pid = task_pid_vnr(tsk);
                if (pid > 0) /* make sure to only use valid results */
                        array[n++] = pid;
        }
        css_task_iter_end(&it);
        length = n;
        /* now sort & (if procs) strip out duplicates */
        sort(array, length, sizeof(pid_t), cmppid, NULL);
        if (type == CGROUP_FILE_PROCS)
                length = pidlist_uniq(array, length);

        l = cgroup_pidlist_find_create(cgrp, type);
        if (!l) {
                kvfree(array);
                return -ENOMEM;
        }

        /* store array, freeing old if necessary */
        kvfree(l->list);
        l->list = array;
        l->length = length;
        *lp = l;
        return 0;
}

/*
 * seq_file methods for the tasks/procs files. The seq_file position is the
 * next pid to display; the seq_file iterator is a pointer to the pid
 * in the cgroup->l->list array.
 */

static void *cgroup_pidlist_start(struct seq_file *s, loff_t *pos)
{
        /*
         * Initially we receive a position value that corresponds to
         * one more than the last pid shown (or 0 on the first call or
         * after a seek to the start). Use a binary-search to find the
         * next pid to display, if any
         */
        struct kernfs_open_file *of = s->private;
        struct cgroup *cgrp = seq_css(s)->cgroup;
        struct cgroup_pidlist *l;
        enum cgroup_filetype type = seq_cft(s)->private;
        int index = 0, pid = *pos;
        int *iter, ret;

        mutex_lock(&cgrp->pidlist_mutex);

        /*
         * !NULL @of->priv indicates that this isn't the first start()
         * after open.  If the matching pidlist is around, we can use that.
         * Look for it.  Note that @of->priv can't be used directly.  It
         * could already have been destroyed.
         */
        if (of->priv)
                of->priv = cgroup_pidlist_find(cgrp, type);

        /*
         * Either this is the first start() after open or the matching
         * pidlist has been destroyed inbetween.  Create a new one.
         */
        if (!of->priv) {
                ret = pidlist_array_load(cgrp, type,
                                         (struct cgroup_pidlist **)&of->priv);
                if (ret)
                        return ERR_PTR(ret);
        }
        l = of->priv;

        if (pid) {
                int end = l->length;

                while (index < end) {
                        int mid = (index + end) / 2;
                        if (l->list[mid] == pid) {
                                index = mid;
                                break;
                        } else if (l->list[mid] <= pid)
                                index = mid + 1;
                        else
                                end = mid;
                }
        }
        /* If we're off the end of the array, we're done */
        if (index >= l->length)
                return NULL;
        /* Update the abstract position to be the actual pid that we found */
        iter = l->list + index;
        *pos = *iter;
        return iter;
}

static void cgroup_pidlist_stop(struct seq_file *s, void *v)
{
        struct kernfs_open_file *of = s->private;
        struct cgroup_pidlist *l = of->priv;

        if (l)
                mod_delayed_work(cgroup_pidlist_destroy_wq, &l->destroy_dwork,
                                 CGROUP_PIDLIST_DESTROY_DELAY);
        mutex_unlock(&seq_css(s)->cgroup->pidlist_mutex);
}

static void *cgroup_pidlist_next(struct seq_file *s, void *v, loff_t *pos)
{
        struct kernfs_open_file *of = s->private;
        struct cgroup_pidlist *l = of->priv;
        pid_t *p = v;
        pid_t *end = l->list + l->length;
        /*
         * Advance to the next pid in the array. If this goes off the
         * end, we're done
         */
        p++;
        if (p >= end) {
                (*pos)++;
                return NULL;
        } else {
                *pos = *p;
                return p;
        }
}

static int cgroup_pidlist_show(struct seq_file *s, void *v)
{
        seq_printf(s, "%d\n", *(int *)v);

        return 0;
}

static ssize_t __cgroup1_procs_write(struct kernfs_open_file *of,
                                     char *buf, size_t nbytes, loff_t off,
                                     bool threadgroup)
{
        struct cgroup *cgrp;
        struct task_struct *task;
        const struct cred *cred, *tcred;
        ssize_t ret;

        cgrp = cgroup_kn_lock_live(of->kn, false);
        if (!cgrp)
                return -ENODEV;

        task = cgroup_procs_write_start(buf, threadgroup);
        ret = PTR_ERR_OR_ZERO(task);
        if (ret)
                goto out_unlock;

        /*
         * Even if we're attaching all tasks in the thread group, we only
         * need to check permissions on one of them.
         */
        cred = current_cred();
        tcred = get_task_cred(task);
        if (!uid_eq(cred->euid, GLOBAL_ROOT_UID) &&
            !uid_eq(cred->euid, tcred->uid) &&
            !uid_eq(cred->euid, tcred->suid))
                ret = -EACCES;
        put_cred(tcred);
        if (ret)
                goto out_finish;

        ret = cgroup_attach_task(cgrp, task, threadgroup);

out_finish:
        cgroup_procs_write_finish(task);
out_unlock:
        cgroup_kn_unlock(of->kn);

        return ret ?: nbytes;
}

static ssize_t cgroup1_procs_write(struct kernfs_open_file *of,
                                   char *buf, size_t nbytes, loff_t off)
{
        return __cgroup1_procs_write(of, buf, nbytes, off, true);
}

static ssize_t cgroup1_tasks_write(struct kernfs_open_file *of,
                                   char *buf, size_t nbytes, loff_t off)
{
        return __cgroup1_procs_write(of, buf, nbytes, off, false);
}

static ssize_t cgroup_release_agent_write(struct kernfs_open_file *of,
                                          char *buf, size_t nbytes, loff_t off)
{
        struct cgroup *cgrp;

        BUILD_BUG_ON(sizeof(cgrp->root->release_agent_path) < PATH_MAX);

        /*
         * Release agent gets called with all capabilities,
         * require capabilities to set release agent.
         */
        if ((of->file->f_cred->user_ns != &init_user_ns) ||
            !capable(CAP_SYS_ADMIN))
                return -EPERM;

        cgrp = cgroup_kn_lock_live(of->kn, false);
        if (!cgrp)
                return -ENODEV;
        spin_lock(&release_agent_path_lock);
        strlcpy(cgrp->root->release_agent_path, strstrip(buf),
                sizeof(cgrp->root->release_agent_path));
        spin_unlock(&release_agent_path_lock);
        cgroup_kn_unlock(of->kn);
        return nbytes;
}

static int cgroup_release_agent_show(struct seq_file *seq, void *v)
{
        struct cgroup *cgrp = seq_css(seq)->cgroup;

        spin_lock(&release_agent_path_lock);
        seq_puts(seq, cgrp->root->release_agent_path);
        spin_unlock(&release_agent_path_lock);
        seq_putc(seq, '\n');
        return 0;
}

static int cgroup_sane_behavior_show(struct seq_file *seq, void *v)
{
        seq_puts(seq, "0\n");
        return 0;
}

static u64 cgroup_read_notify_on_release(struct cgroup_subsys_state *css,
                                         struct cftype *cft)
{
        return notify_on_release(css->cgroup);
}

static int cgroup_write_notify_on_release(struct cgroup_subsys_state *css,
                                          struct cftype *cft, u64 val)
{
        if (val)
                set_bit(CGRP_NOTIFY_ON_RELEASE, &css->cgroup->flags);
        else
                clear_bit(CGRP_NOTIFY_ON_RELEASE, &css->cgroup->flags);
        return 0;
}

static u64 cgroup_clone_children_read(struct cgroup_subsys_state *css,
                                      struct cftype *cft)
{
        return test_bit(CGRP_CPUSET_CLONE_CHILDREN, &css->cgroup->flags);
}

static int cgroup_clone_children_write(struct cgroup_subsys_state *css,
                                       struct cftype *cft, u64 val)
{
        if (val)
                set_bit(CGRP_CPUSET_CLONE_CHILDREN, &css->cgroup->flags);
        else
                clear_bit(CGRP_CPUSET_CLONE_CHILDREN, &css->cgroup->flags);
        return 0;
}

/* cgroup core interface files for the legacy hierarchies */
struct cftype cgroup1_base_files[] = {
        {
                .name = "cgroup.procs",
                .seq_start = cgroup_pidlist_start,
                .seq_next = cgroup_pidlist_next,
                .seq_stop = cgroup_pidlist_stop,
                .seq_show = cgroup_pidlist_show,
                .private = CGROUP_FILE_PROCS,
                .write = cgroup1_procs_write,
        },
        {
                .name = "cgroup.clone_children",
                .read_u64 = cgroup_clone_children_read,
                .write_u64 = cgroup_clone_children_write,
        },
        {
                .name = "cgroup.sane_behavior",
                .flags = CFTYPE_ONLY_ON_ROOT,
                .seq_show = cgroup_sane_behavior_show,
        },
        {
                .name = "tasks",
                .seq_start = cgroup_pidlist_start,
                .seq_next = cgroup_pidlist_next,
                .seq_stop = cgroup_pidlist_stop,
                .seq_show = cgroup_pidlist_show,
                .private = CGROUP_FILE_TASKS,
                .write = cgroup1_tasks_write,
        },
        {
                .name = "notify_on_release",
                .read_u64 = cgroup_read_notify_on_release,
                .write_u64 = cgroup_write_notify_on_release,
        },
        {
                .name = "release_agent",
                .flags = CFTYPE_ONLY_ON_ROOT,
                .seq_show = cgroup_release_agent_show,
                .write = cgroup_release_agent_write,
                .max_write_len = PATH_MAX - 1,
        },
        { }     /* terminate */
};

/* Display information about each subsystem and each hierarchy */
int proc_cgroupstats_show(struct seq_file *m, void *v)
{
        struct cgroup_subsys *ss;
        int i;

        seq_puts(m, "#subsys_name\thierarchy\tnum_cgroups\tenabled\n");
        /*
         * ideally we don't want subsystems moving around while we do this.
         * cgroup_mutex is also necessary to guarantee an atomic snapshot of
         * subsys/hierarchy state.
         */
        mutex_lock(&cgroup_mutex);

        for_each_subsys(ss, i)
                seq_printf(m, "%s\t%d\t%d\t%d\n",
                           ss->legacy_name, ss->root->hierarchy_id,
                           atomic_read(&ss->root->nr_cgrps),
                           cgroup_ssid_enabled(i));

        mutex_unlock(&cgroup_mutex);
        return 0;
}

/**
 * cgroupstats_build - build and fill cgroupstats
 * @stats: cgroupstats to fill information into
 * @dentry: A dentry entry belonging to the cgroup for which stats have
 * been requested.
 *
 * Build and fill cgroupstats so that taskstats can export it to user
 * space.
 */
int cgroupstats_build(struct cgroupstats *stats, struct dentry *dentry)
{
        struct kernfs_node *kn = kernfs_node_from_dentry(dentry);
        struct cgroup *cgrp;
        struct css_task_iter it;
        struct task_struct *tsk;

        /* it should be kernfs_node belonging to cgroupfs and is a directory */
        if (dentry->d_sb->s_type != &cgroup_fs_type || !kn ||
            kernfs_type(kn) != KERNFS_DIR)
                return -EINVAL;

        mutex_lock(&cgroup_mutex);

        /*
         * We aren't being called from kernfs and there's no guarantee on
         * @kn->priv's validity.  For this and css_tryget_online_from_dir(),
         * @kn->priv is RCU safe.  Let's do the RCU dancing.
         */
        rcu_read_lock();
        cgrp = rcu_dereference(*(void __rcu __force **)&kn->priv);
        if (!cgrp || cgroup_is_dead(cgrp)) {
                rcu_read_unlock();
                mutex_unlock(&cgroup_mutex);
                return -ENOENT;
        }
        rcu_read_unlock();

        css_task_iter_start(&cgrp->self, 0, &it);
        while ((tsk = css_task_iter_next(&it))) {
                switch (tsk->state) {
                case TASK_RUNNING:
                        stats->nr_running++;
                        break;
                case TASK_INTERRUPTIBLE:
                        stats->nr_sleeping++;
                        break;
                case TASK_UNINTERRUPTIBLE:
                        stats->nr_uninterruptible++;
                        break;
                case TASK_STOPPED:
                        stats->nr_stopped++;
                        break;
                default:
                        if (delayacct_is_task_waiting_on_io(tsk))
                                stats->nr_io_wait++;
                        break;
                }
        }
        css_task_iter_end(&it);

        mutex_unlock(&cgroup_mutex);
        return 0;
}

void cgroup1_check_for_release(struct cgroup *cgrp)
{
        if (notify_on_release(cgrp) && !cgroup_is_populated(cgrp) &&
            !css_has_online_children(&cgrp->self) && !cgroup_is_dead(cgrp))
                schedule_work(&cgrp->release_agent_work);
}

/*
 * Notify userspace when a cgroup is released, by running the
 * configured release agent with the name of the cgroup (path
 * relative to the root of cgroup file system) as the argument.
 *
 * Most likely, this user command will try to rmdir this cgroup.
 *
 * This races with the possibility that some other task will be
 * attached to this cgroup before it is removed, or that some other
 * user task will 'mkdir' a child cgroup of this cgroup.  That's ok.
 * The presumed 'rmdir' will fail quietly if this cgroup is no longer
 * unused, and this cgroup will be reprieved from its death sentence,
 * to continue to serve a useful existence.  Next time it's released,
 * we will get notified again, if it still has 'notify_on_release' set.
 *
 * The final arg to call_usermodehelper() is UMH_WAIT_EXEC, which
 * means only wait until the task is successfully execve()'d.  The
 * separate release agent task is forked by call_usermodehelper(),
 * then control in this thread returns here, without waiting for the
 * release agent task.  We don't bother to wait because the caller of
 * this routine has no use for the exit status of the release agent
 * task, so no sense holding our caller up for that.
 */
void cgroup1_release_agent(struct work_struct *work)
{
        struct cgroup *cgrp =
                container_of(work, struct cgroup, release_agent_work);
        char *pathbuf = NULL, *agentbuf = NULL;
        char *argv[3], *envp[3];
        int ret;

        mutex_lock(&cgroup_mutex);

        pathbuf = kmalloc(PATH_MAX, GFP_KERNEL);
        agentbuf = kstrdup(cgrp->root->release_agent_path, GFP_KERNEL);
        if (!pathbuf || !agentbuf || !strlen(agentbuf))
                goto out;

        spin_lock_irq(&css_set_lock);
        ret = cgroup_path_ns_locked(cgrp, pathbuf, PATH_MAX, &init_cgroup_ns);
        spin_unlock_irq(&css_set_lock);
        if (ret < 0 || ret >= PATH_MAX)
                goto out;

        argv[0] = agentbuf;
        argv[1] = pathbuf;
        argv[2] = NULL;

        /* minimal command environment */
        envp[0] = "HOME=/";
        envp[1] = "PATH=/sbin:/bin:/usr/sbin:/usr/bin";
        envp[2] = NULL;

        mutex_unlock(&cgroup_mutex);
        call_usermodehelper(argv[0], argv, envp, UMH_WAIT_EXEC);
        goto out_free;
out:
        mutex_unlock(&cgroup_mutex);
out_free:
        kfree(agentbuf);
        kfree(pathbuf);
}

/*
 * cgroup_rename - Only allow simple rename of directories in place.
 */
static int cgroup1_rename(struct kernfs_node *kn, struct kernfs_node *new_parent,
                          const char *new_name_str)
{
        struct cgroup *cgrp = kn->priv;
        int ret;

        /* do not accept '\n' to prevent making /proc/<pid>/cgroup unparsable */
        if (strchr(new_name_str, '\n'))
                return -EINVAL;

        if (kernfs_type(kn) != KERNFS_DIR)
                return -ENOTDIR;
        if (kn->parent != new_parent)
                return -EIO;

        /*
         * We're gonna grab cgroup_mutex which nests outside kernfs
         * active_ref.  kernfs_rename() doesn't require active_ref
         * protection.  Break them before grabbing cgroup_mutex.
         */
        kernfs_break_active_protection(new_parent);
        kernfs_break_active_protection(kn);

        mutex_lock(&cgroup_mutex);

        ret = kernfs_rename(kn, new_parent, new_name_str);
        if (!ret)
                TRACE_CGROUP_PATH(rename, cgrp);

        mutex_unlock(&cgroup_mutex);

        kernfs_unbreak_active_protection(kn);
        kernfs_unbreak_active_protection(new_parent);
        return ret;
}

static int cgroup1_show_options(struct seq_file *seq, struct kernfs_root *kf_root)
{
        struct cgroup_root *root = cgroup_root_from_kf(kf_root);
        struct cgroup_subsys *ss;
        int ssid;

        for_each_subsys(ss, ssid)
                if (root->subsys_mask & (1 << ssid))
                        seq_show_option(seq, ss->legacy_name, NULL);
        if (root->flags & CGRP_ROOT_NOPREFIX)
                seq_puts(seq, ",noprefix");
        if (root->flags & CGRP_ROOT_XATTR)
                seq_puts(seq, ",xattr");
        if (root->flags & CGRP_ROOT_CPUSET_V2_MODE)
                seq_puts(seq, ",cpuset_v2_mode");

        spin_lock(&release_agent_path_lock);
        if (strlen(root->release_agent_path))
                seq_show_option(seq, "release_agent",
                                root->release_agent_path);
        spin_unlock(&release_agent_path_lock);

        if (test_bit(CGRP_CPUSET_CLONE_CHILDREN, &root->cgrp.flags))
                seq_puts(seq, ",clone_children");
        if (strlen(root->name))
                seq_show_option(seq, "name", root->name);
        return 0;
}

enum cgroup1_param {
        Opt_all,
        Opt_clone_children,
        Opt_cpuset_v2_mode,
        Opt_name,
        Opt_none,
        Opt_noprefix,
        Opt_release_agent,
        Opt_xattr,
};

static const struct fs_parameter_spec cgroup1_param_specs[] = {
        fsparam_flag  ("all",           Opt_all),
        fsparam_flag  ("clone_children", Opt_clone_children),
        fsparam_flag  ("cpuset_v2_mode", Opt_cpuset_v2_mode),
        fsparam_string("name",          Opt_name),
        fsparam_flag  ("none",          Opt_none),
        fsparam_flag  ("noprefix",      Opt_noprefix),
        fsparam_string("release_agent", Opt_release_agent),
        fsparam_flag  ("xattr",         Opt_xattr),
        {}
};

const struct fs_parameter_description cgroup1_fs_parameters = {
        .name           = "cgroup1",
        .specs          = cgroup1_param_specs,
};

int cgroup1_parse_param(struct fs_context *fc, struct fs_parameter *param)
{
        struct cgroup_fs_context *ctx = cgroup_fc2context(fc);
        struct cgroup_subsys *ss;
        struct fs_parse_result result;
        int opt, i;

        opt = fs_parse(fc, &cgroup1_fs_parameters, param, &result);
        if (opt == -ENOPARAM) {
                if (strcmp(param->key, "source") == 0) {
                        if (param->type != fs_value_is_string)
                                return invalf(fc, "Non-string source");
                        if (fc->source)
                                return invalf(fc, "Multiple sources not supported");
                        fc->source = param->string;
                        param->string = NULL;
                        return 0;
                }
                for_each_subsys(ss, i) {
                        if (strcmp(param->key, ss->legacy_name))
                                continue;
                        ctx->subsys_mask |= (1 << i);
                        return 0;
                }
                return cg_invalf(fc, "cgroup1: Unknown subsys name '%s'", param->key);
        }
        if (opt < 0)
                return opt;

        switch (opt) {
        case Opt_none:
                /* Explicitly have no subsystems */
                ctx->none = true;
                break;
        case Opt_all:
                ctx->all_ss = true;
                break;
        case Opt_noprefix:
                ctx->flags |= CGRP_ROOT_NOPREFIX;
                break;
        case Opt_clone_children:
                ctx->cpuset_clone_children = true;
                break;
        case Opt_cpuset_v2_mode:
                ctx->flags |= CGRP_ROOT_CPUSET_V2_MODE;
                break;
        case Opt_xattr:
                ctx->flags |= CGRP_ROOT_XATTR;
                break;
        case Opt_release_agent:
                /* Specifying two release agents is forbidden */
                if (ctx->release_agent)
                        return cg_invalf(fc, "cgroup1: release_agent respecified");
                /*
                 * Release agent gets called with all capabilities,
                 * require capabilities to set release agent.
                 */
                if ((fc->user_ns != &init_user_ns) || !capable(CAP_SYS_ADMIN))
                        return cg_invalf(fc, "cgroup1: Setting release_agent not allowed");
                ctx->release_agent = param->string;
                param->string = NULL;
                break;
        case Opt_name:
                /* blocked by boot param? */
                if (cgroup_no_v1_named)
                        return -ENOENT;
                /* Can't specify an empty name */
                if (!param->size)
                        return cg_invalf(fc, "cgroup1: Empty name");
                if (param->size > MAX_CGROUP_ROOT_NAMELEN - 1)
                        return cg_invalf(fc, "cgroup1: Name too long");
                /* Must match [\w.-]+ */
                for (i = 0; i < param->size; i++) {
                        char c = param->string[i];
                        if (isalnum(c))
                                continue;
                        if ((c == '.') || (c == '-') || (c == '_'))
                                continue;
                        return cg_invalf(fc, "cgroup1: Invalid name");
                }
                /* Specifying two names is forbidden */
                if (ctx->name)
                        return cg_invalf(fc, "cgroup1: name respecified");
                ctx->name = param->string;
                param->string = NULL;
                break;
        }
        return 0;
}

static int check_cgroupfs_options(struct fs_context *fc)
{
        struct cgroup_fs_context *ctx = cgroup_fc2context(fc);
        u16 mask = U16_MAX;
        u16 enabled = 0;
        struct cgroup_subsys *ss;
        int i;

#ifdef CONFIG_CPUSETS
        mask = ~((u16)1 << cpuset_cgrp_id);
#endif
        for_each_subsys(ss, i)
                if (cgroup_ssid_enabled(i) && !cgroup1_ssid_disabled(i))
                        enabled |= 1 << i;

        ctx->subsys_mask &= enabled;

        /*
         * In absense of 'none', 'name=' or subsystem name options,
         * let's default to 'all'.
         */
        if (!ctx->subsys_mask && !ctx->none && !ctx->name)
                ctx->all_ss = true;

        if (ctx->all_ss) {
                /* Mutually exclusive option 'all' + subsystem name */
                if (ctx->subsys_mask)
                        return cg_invalf(fc, "cgroup1: subsys name conflicts with all");
                /* 'all' => select all the subsystems */
                ctx->subsys_mask = enabled;
        }

        /*
         * We either have to specify by name or by subsystems. (So all
         * empty hierarchies must have a name).
         */
        if (!ctx->subsys_mask && !ctx->name)
                return cg_invalf(fc, "cgroup1: Need name or subsystem set");

        /*
         * Option noprefix was introduced just for backward compatibility
         * with the old cpuset, so we allow noprefix only if mounting just
         * the cpuset subsystem.
         */
        if ((ctx->flags & CGRP_ROOT_NOPREFIX) && (ctx->subsys_mask & mask))
                return cg_invalf(fc, "cgroup1: noprefix used incorrectly");

        /* Can't specify "none" and some subsystems */
        if (ctx->subsys_mask && ctx->none)
                return cg_invalf(fc, "cgroup1: none used incorrectly");

        return 0;
}

int cgroup1_reconfigure(struct fs_context *fc)
{
        struct cgroup_fs_context *ctx = cgroup_fc2context(fc);
        struct kernfs_root *kf_root = kernfs_root_from_sb(fc->root->d_sb);
        struct cgroup_root *root = cgroup_root_from_kf(kf_root);
        int ret = 0;
        u16 added_mask, removed_mask;

        cgroup_lock_and_drain_offline(&cgrp_dfl_root.cgrp);

        /* See what subsystems are wanted */
        ret = check_cgroupfs_options(fc);
        if (ret)
                goto out_unlock;

        if (ctx->subsys_mask != root->subsys_mask || ctx->release_agent)
                pr_warn("option changes via remount are deprecated (pid=%d comm=%s)\n",
                        task_tgid_nr(current), current->comm);

        added_mask = ctx->subsys_mask & ~root->subsys_mask;
        removed_mask = root->subsys_mask & ~ctx->subsys_mask;

        /* Don't allow flags or name to change at remount */
        if ((ctx->flags ^ root->flags) ||
            (ctx->name && strcmp(ctx->name, root->name))) {
                cg_invalf(fc, "option or name mismatch, new: 0x%x \"%s\", old: 0x%x \"%s\"",
                       ctx->flags, ctx->name ?: "", root->flags, root->name);
                ret = -EINVAL;
                goto out_unlock;
        }

        /* remounting is not allowed for populated hierarchies */
        if (!list_empty(&root->cgrp.self.children)) {
                ret = -EBUSY;
                goto out_unlock;
        }

        ret = rebind_subsystems(root, added_mask);
        if (ret)
                goto out_unlock;

        WARN_ON(rebind_subsystems(&cgrp_dfl_root, removed_mask));

        if (ctx->release_agent) {
                spin_lock(&release_agent_path_lock);
                strcpy(root->release_agent_path, ctx->release_agent);
                spin_unlock(&release_agent_path_lock);
        }

        trace_cgroup_remount(root);

 out_unlock:
        mutex_unlock(&cgroup_mutex);
        return ret;
}

struct kernfs_syscall_ops cgroup1_kf_syscall_ops = {
        .rename                 = cgroup1_rename,
        .show_options           = cgroup1_show_options,
        .mkdir                  = cgroup_mkdir,
        .rmdir                  = cgroup_rmdir,
        .show_path              = cgroup_show_path,
};

/*
 * The guts of cgroup1 mount - find or create cgroup_root to use.
 * Called with cgroup_mutex held; returns 0 on success, -E... on
 * error and positive - in case when the candidate is busy dying.
 * On success it stashes a reference to cgroup_root into given
 * cgroup_fs_context; that reference is *NOT* counting towards the
 * cgroup_root refcount.
 */
static int cgroup1_root_to_use(struct fs_context *fc)
{
        struct cgroup_fs_context *ctx = cgroup_fc2context(fc);
        struct cgroup_root *root;
        struct cgroup_subsys *ss;
        int i, ret;

        /* First find the desired set of subsystems */
        ret = check_cgroupfs_options(fc);
        if (ret)
                return ret;

        /*
         * Destruction of cgroup root is asynchronous, so subsystems may
         * still be dying after the previous unmount.  Let's drain the
         * dying subsystems.  We just need to ensure that the ones
         * unmounted previously finish dying and don't care about new ones
         * starting.  Testing ref liveliness is good enough.
         */
        for_each_subsys(ss, i) {
                if (!(ctx->subsys_mask & (1 << i)) ||
                    ss->root == &cgrp_dfl_root)
                        continue;

                if (!percpu_ref_tryget_live(&ss->root->cgrp.self.refcnt))
                        return 1;       /* restart */
                cgroup_put(&ss->root->cgrp);
        }

        for_each_root(root) {
                bool name_match = false;

                if (root == &cgrp_dfl_root)
                        continue;

                /*
                 * If we asked for a name then it must match.  Also, if
                 * name matches but sybsys_mask doesn't, we should fail.
                 * Remember whether name matched.
                 */
                if (ctx->name) {
                        if (strcmp(ctx->name, root->name))
                                continue;
                        name_match = true;
                }

                /*
                 * If we asked for subsystems (or explicitly for no
                 * subsystems) then they must match.
                 */
                if ((ctx->subsys_mask || ctx->none) &&
                    (ctx->subsys_mask != root->subsys_mask)) {
                        if (!name_match)
                                continue;
                        return -EBUSY;
                }

                if (root->flags ^ ctx->flags)
                        pr_warn("new mount options do not match the existing superblock, will be ignored\n");

                ctx->root = root;
                return 0;
        }

        /*
         * No such thing, create a new one.  name= matching without subsys
         * specification is allowed for already existing hierarchies but we
         * can't create new one without subsys specification.
         */
        if (!ctx->subsys_mask && !ctx->none)
                return cg_invalf(fc, "cgroup1: No subsys list or none specified");

        /* Hierarchies may only be created in the initial cgroup namespace. */
        if (ctx->ns != &init_cgroup_ns)
                return -EPERM;

        root = kzalloc(sizeof(*root), GFP_KERNEL);
        if (!root)
                return -ENOMEM;

        ctx->root = root;
        init_cgroup_root(ctx);

        ret = cgroup_setup_root(root, ctx->subsys_mask);
        if (ret)
                cgroup_free_root(root);
        return ret;
}

int cgroup1_get_tree(struct fs_context *fc)
{
        struct cgroup_fs_context *ctx = cgroup_fc2context(fc);
        int ret;

        /* Check if the caller has permission to mount. */
        if (!ns_capable(ctx->ns->user_ns, CAP_SYS_ADMIN))
                return -EPERM;

        cgroup_lock_and_drain_offline(&cgrp_dfl_root.cgrp);

        ret = cgroup1_root_to_use(fc);
        if (!ret && !percpu_ref_tryget_live(&ctx->root->cgrp.self.refcnt))
                ret = 1;        /* restart */

        mutex_unlock(&cgroup_mutex);

        if (!ret)
                ret = cgroup_do_get_tree(fc);

        if (!ret && percpu_ref_is_dying(&ctx->root->cgrp.self.refcnt)) {
                fc_drop_locked(fc);
                ret = 1;
        }

        if (unlikely(ret > 0)) {
                msleep(10);
                return restart_syscall();
        }
        return ret;
}

static int __init cgroup1_wq_init(void)
{
        /*
         * Used to destroy pidlists and separate to serve as flush domain.
         * Cap @max_active to 1 too.
         */
        cgroup_pidlist_destroy_wq = alloc_workqueue("cgroup_pidlist_destroy",
                                                    0, 1);
        BUG_ON(!cgroup_pidlist_destroy_wq);
        return 0;
}
core_initcall(cgroup1_wq_init);

static int __init cgroup_no_v1(char *str)
{
        struct cgroup_subsys *ss;
        char *token;
        int i;

        while ((token = strsep(&str, ",")) != NULL) {
                if (!*token)
                        continue;

                if (!strcmp(token, "all")) {
                        cgroup_no_v1_mask = U16_MAX;
                        continue;
                }

                if (!strcmp(token, "named")) {
                        cgroup_no_v1_named = true;
                        continue;
                }

                for_each_subsys(ss, i) {
                        if (strcmp(token, ss->name) &&
                            strcmp(token, ss->legacy_name))
                                continue;

                        cgroup_no_v1_mask |= 1 << i;
                }
        }
        return 1;
}
__setup("cgroup_no_v1=", cgroup_no_v1);