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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>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>
This commit is contained in:
Oleg Nesterov 2008-05-23 13:04:41 -07:00 committed by Linus Torvalds
parent dfc7064500
commit da7978b034
2 changed files with 8 additions and 2 deletions
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7
kernel/exit.c
View file

@ -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);

3
kernel/signal.c
View file

@ -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))