From ba661292a2bc6ddd305a212b0526e5dc22195fe7 Mon Sep 17 00:00:00 2001 From: Oleg Nesterov Date: Wed, 23 Jul 2008 20:52:05 +0400 Subject: posix-timers: fix posix_timer_event() vs dequeue_signal() race The bug was reported and analysed by Mark McLoughlin , the patch is based on his and Roland's suggestions. posix_timer_event() always rewrites the pre-allocated siginfo before sending the signal. Most of the written info is the same all the time, but memset(0) is very wrong. If ->sigq is queued we can race with collect_signal() which can fail to find this siginfo looking at .si_signo, or copy_siginfo() can copy the wrong .si_code/si_tid/etc. In short, sys_timer_settime() can in fact stop the active timer, or the user can receive the siginfo with the wrong .si_xxx values. Move "memset(->info, 0)" from posix_timer_event() to alloc_posix_timer(), change send_sigqueue() to set .si_overrun = 0 when ->sigq is not queued. It would be nice to move the whole sigq->info initialization from send to create path, but this is not easy to do without uglifying timer_create() further. As Roland rightly pointed out, we need more cleanups/fixes here, see the "FIXME" comment in the patch. Hopefully this patch makes sense anyway, and it can mask the most bad implications. Reported-by: Mark McLoughlin Signed-off-by: Oleg Nesterov Cc: Mark McLoughlin Cc: Oliver Pinter Cc: Roland McGrath Cc: stable@kernel.org Cc: Andrew Morton Signed-off-by: Thomas Gleixner kernel/posix-timers.c | 17 +++++++++++++---- kernel/signal.c | 1 + 2 files changed, 14 insertions(+), 4 deletions(-) --- kernel/signal.c | 1 + 1 file changed, 1 insertion(+) (limited to 'kernel/signal.c') diff --git a/kernel/signal.c b/kernel/signal.c index 72bb4f51f96..13fab983835 100644 --- a/kernel/signal.c +++ b/kernel/signal.c @@ -1280,6 +1280,7 @@ int send_sigqueue(struct sigqueue *q, struct task_struct *t, int group) q->info.si_overrun++; goto out; } + q->info.si_overrun = 0; signalfd_notify(t, sig); pending = group ? &t->signal->shared_pending : &t->pending; -- cgit v1.2.2