signals: fix sigqueue_free() vs __exit_signal() race (da7978b0) · Commits · 戴 / test

__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 <oleg@tv-sign.ru> Acked-by:

Roland McGrath <roland@redhat.com> Signed-off-by:

Andrew Morton <akpm@linux-foundation.org> Signed-off-by:

Linus Torvalds <torvalds@linux-foundation.org>

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))

Admin message