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Commit e752dd6c authored by Oleg Nesterov's avatar Oleg Nesterov Committed by Linus Torvalds
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[PATCH] fix send_sigqueue() vs thread exit race 



posix_timer_event() first checks that the thread (SIGEV_THREAD_ID case)
does not have PF_EXITING flag, then it calls send_sigqueue() which locks
task list.  But if the thread exits in between the kernel will oops
(->sighand == NULL after __exit_sighand).

This patch moves the PF_EXITING check into the send_sigqueue(), it must be
done atomically under tasklist_lock.  When send_sigqueue() detects exiting
thread it returns -1.  In that case posix_timer_event will send the signal
to thread group.

Also, this patch fixes task_struct use-after-free in posix_timer_event.

Signed-off-by: default avatarOleg Nesterov <oleg@tv-sign.ru>
Cc: Thomas Gleixner <tglx@linutronix.de>
Signed-off-by: default avatarAndrew Morton <akpm@osdl.org>
Signed-off-by: default avatarLinus Torvalds <torvalds@osdl.org>
parent a97c9bf3

kernel/posix-timers.c

+15 −13
Original line number Diff line number Diff line
@@ -427,22 +427,24 @@ int posix_timer_event(struct k_itimer *timr,int si_private) 
	timr->sigq->info.si_code = SI_TIMER;

	timr->sigq->info.si_tid = timr->it_id;

	timr->sigq->info.si_value = timr->it_sigev_value;



	if (timr->it_sigev_notify & SIGEV_THREAD_ID) {

		if (unlikely(timr->it_process->flags & PF_EXITING)) {

		struct task_struct *leader;

		int ret = send_sigqueue(timr->it_sigev_signo, timr->sigq,

					timr->it_process);



		if (likely(ret >= 0))

			return ret;



		timr->it_sigev_notify = SIGEV_SIGNAL;

		leader = timr->it_process->group_leader;

		put_task_struct(timr->it_process);

			timr->it_process = timr->it_process->group_leader;

			goto group;

		timr->it_process = leader;

	}

		return send_sigqueue(timr->it_sigev_signo, timr->sigq,

			timr->it_process);

	}

	else {

	group:



	return send_group_sigqueue(timr->it_sigev_signo, timr->sigq,

				   timr->it_process);

}

}

EXPORT_SYMBOL_GPL(posix_timer_event);



/*

kernel/signal.c

+12 −10
Original line number Diff line number Diff line
@@ -1366,14 +1366,14 @@ send_sigqueue(int sig, struct sigqueue *q, struct task_struct *p) 
	unsigned long flags;

	int ret = 0;



	/*

	 * We need the tasklist lock even for the specific

	 * thread case (when we don't need to follow the group

	 * lists) in order to avoid races with "p->sighand"

	 * going away or changing from under us.

	 */

	BUG_ON(!(q->flags & SIGQUEUE_PREALLOC));

	read_lock(&tasklist_lock);



	if (unlikely(p->flags & PF_EXITING)) {

		ret = -1;

		goto out_err;

	}



	spin_lock_irqsave(&p->sighand->siglock, flags);



	if (unlikely(!list_empty(&q->list))) {
@@ -1400,8 +1400,10 @@ send_sigqueue(int sig, struct sigqueue *q, struct task_struct *p) 


out:

	spin_unlock_irqrestore(&p->sighand->siglock, flags);

out_err:

	read_unlock(&tasklist_lock);

	return(ret);



	return ret;

}



int