Release 4.15 kernel/cgroup/cgroup-v1.c

#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 <trace/events/cgroup.h>

/*
 * 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;

/*
 * 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);
}

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/**
 * 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;
}
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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_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;
}

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/*
 * 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;
};

/*
 * The following two functions "fix" the issue where there are more pids
 * than kmalloc will give memory for; in such cases, we use vmalloc/vfree.
 * TODO: replace with a kernel-wide solution to this problem
 */

#define PIDLIST_TOO_LARGE(c) ((c) * sizeof(pid_t) > (PAGE_SIZE * 2))


static void *pidlist_allocate(int count)
{
	if (PIDLIST_TOO_LARGE(count))
		return vmalloc(count * sizeof(pid_t));
	else
		return kmalloc(count * sizeof(pid_t), GFP_KERNEL);
}

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static void pidlist_free(void *p)
{
	kvfree(p);
}

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/*
 * 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));
}

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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);
		pidlist_free(l->list);
		put_pid_ns(l->key.ns);
		tofree = l;
	}

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

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/*
 * 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;
}

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/*
 * 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;
}

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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;
}

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/*
 * 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;
}

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/**
 * cgroup_task_count - count the number of tasks in a cgroup.
 * @cgrp: the cgroup in question
 */


int cgroup_task_count(const struct cgroup *cgrp)
{
	int count = 0;
	struct cgrp_cset_link *link;

	spin_lock_irq(&css_set_lock);
	list_for_each_entry(link, &cgrp->cset_links, cset_link)
		count += link->cset->nr_tasks;
	spin_unlock_irq(&css_set_lock);
	return count;
}

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/*
 * 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 = pidlist_allocate(length);
	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) {
		pidlist_free(array);
		return -ENOMEM;
	}

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

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/*
 * 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;
}

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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);
}

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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) {
		return NULL;
	} else {
		*pos = *p;
		return p;
	}
}

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

	return 0;
}

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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;
}

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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);
}

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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);
}

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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);

	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;
}

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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;
}

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

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

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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;
}

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

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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;
}

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/* 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 */


static 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;
}

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static int cgroupstats_open(struct inode *inode, struct file *file)
{
	return single_open(file, proc_cgroupstats_show, NULL);
}

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const struct file_operations proc_cgroupstats_operations = {