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Commit da7978b0 authored by Oleg Nesterov's avatar Oleg Nesterov Committed by Linus Torvalds
Browse files

signals: fix sigqueue_free() vs __exit_signal() race 



__exit_signal() does flush_sigqueue(tsk->pending) outside of ->siglock.
This can race with another thread doing sigqueue_free(), we can free the
same SIGQUEUE_PREALLOC sigqueue twice or corrupt the pending->list.

Note that even sys_exit_group() can trigger this race, not only
sys_timer_delete().

Move the callsite of flush_sigqueue(tsk->pending) under ->siglock.

This patch doesn't touch flush_sigqueue(->shared_pending) below, it is
called when there are no other threads which can play with signals, and
sigqueue_free() can't be used outside of our thread group.

Signed-off-by: default avatarOleg Nesterov <oleg@tv-sign.ru>
Acked-by: default avatarRoland McGrath <roland@redhat.com>
Signed-off-by: default avatarAndrew Morton <akpm@linux-foundation.org>
Signed-off-by: default avatarLinus Torvalds <torvalds@linux-foundation.org>
parent dfc70645

kernel/exit.c

+6 −1
Original line number Diff line number Diff line
@@ -126,6 +126,12 @@ static void __exit_signal(struct task_struct *tsk) 


	__unhash_process(tsk);



	/*

	 * Do this under ->siglock, we can race with another thread

	 * doing sigqueue_free() if we have SIGQUEUE_PREALLOC signals.

	 */

	flush_sigqueue(&tsk->pending);



	tsk->signal = NULL;

	tsk->sighand = NULL;

	spin_unlock(&sighand->siglock);
@@ -133,7 +139,6 @@ static void __exit_signal(struct task_struct *tsk) 


	__cleanup_sighand(sighand);

	clear_tsk_thread_flag(tsk,TIF_SIGPENDING);

	flush_sigqueue(&tsk->pending);

	if (sig) {

		flush_sigqueue(&sig->shared_pending);

		taskstats_tgid_free(sig);

kernel/signal.c

+2 −1
Original line number Diff line number Diff line
@@ -1242,7 +1242,8 @@ void sigqueue_free(struct sigqueue *q) 
	/*

	 * If the signal is still pending remove it from the

	 * pending queue. We must hold ->siglock while testing

	 * q->list to serialize with collect_signal().

	 * q->list to serialize with collect_signal() or with

	 * __exit_signal()->flush_sigqueue().

	 */

	spin_lock_irqsave(lock, flags);

	if (!list_empty(&q->list))