Commit 6dda81f4 authored Apr 02, 2009 by Oleg Nesterov Committed by Linus Torvalds Apr 02, 2009

pids: document task_pgrp/task_session is not safe without tasklist/rcu



Even if task == current, it is not safe to dereference the result of
task_pgrp/task_session.  We can race with another thread which changes the
special pid via setpgid/setsid.

Document this.  The next 2 patches give an example of the unsafe usage, we
have more bad users.

[akpm@linux-foundation.org: coding-style fixes]
Signed-off-by: Oleg Nesterov <oleg@redhat.com>
Cc: Louis Rilling <Louis.Rilling@kerlabs.com>
Cc: "Eric W. Biederman" <ebiederm@xmission.com>
Cc: Pavel Emelyanov <xemul@openvz.org>
Cc: Sukadev Bhattiprolu <sukadev@linux.vnet.ibm.com>
Cc: Roland McGrath <roland@redhat.com>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>

parent 8e654fba

include/linux/sched.h

+5 −0

Original line number	Diff line number	Diff line
		@@ -1489,6 +1489,11 @@ static inline struct pid task_tgid(struct task_struct task)
		return task->group_leader->pids[PIDTYPE_PID].pid;
		}

		/*
		* Without tasklist or rcu lock it is not safe to dereference
		* the result of task_pgrp/task_session even if task == current,
		* we can race with another thread doing sys_setsid/sys_setpgid.
		*/
		static inline struct pid task_pgrp(struct task_struct task)
		{
		return task->group_leader->pids[PIDTYPE_PGID].pid;