Messages in this thread Patch in this message | | | Date | Sat, 17 May 2008 19:14:18 +0400 | From | Oleg Nesterov <> | Subject | [PATCH 1/3] signals: fix sigqueue_free() vs __exit_signal() race |
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__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>
--- 25/kernel/exit.c~1_SQFREE_EXIT_RACE 2008-05-17 16:03:29.000000000 +0400 +++ 25/kernel/exit.c 2008-05-17 16:22:07.000000000 +0400 @@ -125,6 +125,12 @@ static void __exit_signal(struct task_st __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); @@ -132,7 +138,6 @@ static void __exit_signal(struct task_st __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); --- 25/kernel/signal.c~1_SQFREE_EXIT_RACE 2008-05-17 16:03:29.000000000 +0400 +++ 25/kernel/signal.c 2008-05-17 16:22:07.000000000 +0400 @@ -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))
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