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

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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>
This commit is contained in:
Oleg Nesterov 2009-04-02 16:58:35 -07:00 committed by Linus Torvalds
parent 8e654fba4a
commit 6dda81f438
1 changed files with 5 additions and 0 deletions
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5
include/linux/sched.h
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@ -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;