Commit d855a4b7 authored by Oleg Nesterov's avatar Oleg Nesterov Committed by Linus Torvalds
Browse files

proc: don't (ab)use ->group_leader in proc_task_readdir() paths 



proc_task_readdir() does not really need "leader", first_tid() has to
revalidate it anyway.  Just pass proc_pid(inode) to first_tid() instead,
it can do pid_task(PIDTYPE_PID) itself and read ->group_leader only if
necessary.

The patch also extracts the "inode is dead" code from
pid_delete_dentry(dentry) into the new trivial helper,
proc_inode_is_dead(inode), proc_task_readdir() uses it to return -ENOENT
if this dir was removed.

This is a bit racy, but the race is very inlikely and the getdents() after
openndir() can see the empty "." + ".." dir only once.

Signed-off-by: default avatarOleg Nesterov <oleg@redhat.com>
Cc: "Eric W. Biederman" <ebiederm@xmission.com>
Cc: Michal Hocko <mhocko@suse.cz>
Cc: Sameer Nanda <snanda@chromium.org>
Cc: Sergey Dyasly <dserrg@gmail.com>
Signed-off-by: default avatarAndrew Morton <akpm@linux-foundation.org>
Signed-off-by: default avatarLinus Torvalds <torvalds@linux-foundation.org>
parent c986c14a

fs/proc/base.c

+24 −28
Original line number Diff line number Diff line
@@ -1658,13 +1658,18 @@ int pid_revalidate(struct dentry *dentry, unsigned int flags) 
	return 0;

}



static inline bool proc_inode_is_dead(struct inode *inode)

{

	return !proc_pid(inode)->tasks[PIDTYPE_PID].first;

}



int pid_delete_dentry(const struct dentry *dentry)

{

	/* Is the task we represent dead?

	 * If so, then don't put the dentry on the lru list,

	 * kill it immediately.

	 */

	return !proc_pid(dentry->d_inode)->tasks[PIDTYPE_PID].first;

	return proc_inode_is_dead(dentry->d_inode);

}



const struct dentry_operations pid_dentry_operations =
@@ -3092,34 +3097,35 @@ out_no_task: 
 * In the case of a seek we start with the leader and walk nr

 * threads past it.

 */

static struct task_struct *first_tid(struct task_struct *leader,

		int tid, int nr, struct pid_namespace *ns)

static struct task_struct *first_tid(struct pid *pid, int tid,

					int nr, struct pid_namespace *ns)

{

	struct task_struct *pos;

	struct task_struct *pos, *task;



	rcu_read_lock();

	/* Attempt to start with the pid of a thread */

	task = pid_task(pid, PIDTYPE_PID);

	if (!task)

		goto fail;



	/* Attempt to start with the tid of a thread */

	if (tid && (nr > 0)) {

		pos = find_task_by_pid_ns(tid, ns);

		if (pos && (pos->group_leader == leader))

		if (pos && same_thread_group(pos, task))

			goto found;

	}



	/* If nr exceeds the number of threads there is nothing todo */

	if (nr && nr >= get_nr_threads(leader))

		goto fail;

	/* It could be unhashed before we take rcu lock */

	if (!pid_alive(leader))

	if (nr && nr >= get_nr_threads(task))

		goto fail;



	/* If we haven't found our starting place yet start

	 * with the leader and walk nr threads forward.

	 */

	pos = leader;

	pos = task = task->group_leader;

	do {

		if (nr-- <= 0)

			goto found;

	} while_each_thread(leader, pos);

	} while_each_thread(task, pos);

fail:

	pos = NULL;

	goto out;
@@ -3155,25 +3161,16 @@ static struct task_struct *next_tid(struct task_struct *start) 
/* for the /proc/TGID/task/ directories */

static int proc_task_readdir(struct file *file, struct dir_context *ctx)

{

	struct task_struct *leader = NULL;

	struct task_struct *task = get_proc_task(file_inode(file));

	struct inode *inode = file_inode(file);

	struct task_struct *task;

	struct pid_namespace *ns;

	int tid;



	if (!task)

		return -ENOENT;

	rcu_read_lock();

	if (pid_alive(task)) {

		leader = task->group_leader;

		get_task_struct(leader);

	}

	rcu_read_unlock();

	put_task_struct(task);

	if (!leader)

	if (proc_inode_is_dead(inode))

		return -ENOENT;



	if (!dir_emit_dots(file, ctx))

		goto out;

		return 0;



	/* f_version caches the tgid value that the last readdir call couldn't

	 * return. lseek aka telldir automagically resets f_version to 0.
@@ -3181,7 +3178,7 @@ static int proc_task_readdir(struct file *file, struct dir_context *ctx) 
	ns = file->f_dentry->d_sb->s_fs_info;

	tid = (int)file->f_version;

	file->f_version = 0;

	for (task = first_tid(leader, tid, ctx->pos - 2, ns);

	for (task = first_tid(proc_pid(inode), tid, ctx->pos - 2, ns);

	     task;

	     task = next_tid(task), ctx->pos++) {

		char name[PROC_NUMBUF];
@@ -3197,8 +3194,7 @@ static int proc_task_readdir(struct file *file, struct dir_context *ctx) 
			break;

		}

	}

out:

	put_task_struct(leader);



	return 0;

}

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