[PATCH] fix send_sigqueue() vs thread exit race
posix_timer_event() first checks that the thread (SIGEV_THREAD_ID case)
does not have PF_EXITING flag, then it calls send_sigqueue() which locks
task list. But if the thread exits in between the kernel will oops
(->sighand == NULL after __exit_sighand).
This patch moves the PF_EXITING check into the send_sigqueue(), it must be
done atomically under tasklist_lock. When send_sigqueue() detects exiting
thread it returns -1. In that case posix_timer_event will send the signal
to thread group.
Also, this patch fixes task_struct use-after-free in posix_timer_event.
Signed-off-by: Oleg Nesterov <oleg@tv-sign.ru>
Cc: Thomas Gleixner <tglx@linutronix.de>
Signed-off-by: Andrew Morton <akpm@osdl.org>
Signed-off-by: Linus Torvalds <torvalds@osdl.org>
diff --git a/kernel/signal.c b/kernel/signal.c
index 56e33df..4980a07 100644
--- a/kernel/signal.c
+++ b/kernel/signal.c
@@ -1366,16 +1366,16 @@
unsigned long flags;
int ret = 0;
- /*
- * We need the tasklist lock even for the specific
- * thread case (when we don't need to follow the group
- * lists) in order to avoid races with "p->sighand"
- * going away or changing from under us.
- */
BUG_ON(!(q->flags & SIGQUEUE_PREALLOC));
- read_lock(&tasklist_lock);
+ read_lock(&tasklist_lock);
+
+ if (unlikely(p->flags & PF_EXITING)) {
+ ret = -1;
+ goto out_err;
+ }
+
spin_lock_irqsave(&p->sighand->siglock, flags);
-
+
if (unlikely(!list_empty(&q->list))) {
/*
* If an SI_TIMER entry is already queue just increment
@@ -1385,7 +1385,7 @@
BUG();
q->info.si_overrun++;
goto out;
- }
+ }
/* Short-circuit ignored signals. */
if (sig_ignored(p, sig)) {
ret = 1;
@@ -1400,8 +1400,10 @@
out:
spin_unlock_irqrestore(&p->sighand->siglock, flags);
+out_err:
read_unlock(&tasklist_lock);
- return(ret);
+
+ return ret;
}
int