signals: fix sigqueue_free() vs __exit_signal() race

da7978b0 · Oleg Nesterov <[email protected]> · 2008-05-23 13:04:41 -07:00

__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 <[email protected]>
Acked-by: Roland McGrath <[email protected]>
Signed-off-by: Andrew Morton <[email protected]>
Signed-off-by: Linus Torvalds <[email protected]>

Commit: da7978b0348d497688541e2d2f5739aa2a2c334f
Parents: dfc70645

Changes

2 files changed · +8 −2

File	Status	Add	Del	Content
kernel/exit.c	modified	+6	−1	View file
kernel/signal.c	modified	+2	−1	View file

kernel/exit.c

View file

diff --git a/kernel/exit.c b/kernel/exit.c
index 1510f78..8f6185e 100644
--- a/kernel/exit.c
+++ b/kernel/exit.c
@@ -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

View file

diff --git a/kernel/signal.c b/kernel/signal.c
index 72bb4f5..12ffea7 100644
--- a/kernel/signal.c
+++ b/kernel/signal.c
@@ -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))