From: Oleg Nesterov Date: Fri, 23 May 2008 20:04:41 +0000 (-0700) Subject: signals: fix sigqueue_free() vs __exit_signal() race X-Git-Tag: v2.6.26-rc4~34 X-Git-Url: https://err.no/cgi-bin/gitweb.cgi?a=commitdiff_plain;h=da7978b0348d497688541e2d2f5739aa2a2c334f;p=linux-2.6 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: Oleg Nesterov Acked-by: Roland McGrath Signed-off-by: Andrew Morton Signed-off-by: Linus Torvalds --- diff --git a/kernel/exit.c b/kernel/exit.c index 1510f78a0f..8f6185e69b 100644 --- a/kernel/exit.c +++ b/kernel/exit.c @@ -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); diff --git a/kernel/signal.c b/kernel/signal.c index 72bb4f51f9..12ffea7c20 100644 --- a/kernel/signal.c +++ b/kernel/signal.c @@ -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))