The patch titled
signals: fix sigqueue_free() vs __exit_signal() race
has been added to the -mm tree. Its filename is
signals-fix-sigqueue_free-vs-__exit_signal-race.patch
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------------------------------------------------------
Subject: signals: fix sigqueue_free() vs __exit_signal() race
From: Oleg Nesterov <oleg@xxxxxxxxxx>
__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@xxxxxxxxxx>
Acked-by: Roland McGrath <roland@xxxxxxxxxx>
Signed-off-by: Andrew Morton <akpm@xxxxxxxxxxxxxxxxxxxx>
---
kernel/exit.c | 7 ++++++-
kernel/signal.c | 3 ++-
2 files changed, 8 insertions(+), 2 deletions(-)
diff -puN kernel/exit.c~signals-fix-sigqueue_free-vs-__exit_signal-race kernel/exit.c
--- a/kernel/exit.c~signals-fix-sigqueue_free-vs-__exit_signal-race
+++ a/kernel/exit.c
@@ -126,6 +126,12 @@ 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);
@@ -133,7 +139,6 @@ 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);
diff -puN kernel/signal.c~signals-fix-sigqueue_free-vs-__exit_signal-race kernel/signal.c
--- a/kernel/signal.c~signals-fix-sigqueue_free-vs-__exit_signal-race
+++ a/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))
_
Patches currently in -mm which might be from oleg@xxxxxxxxxx are
signals-fix-sigqueue_free-vs-__exit_signal-race.patch
posix-timers-timer_delete-remove-the-bogus-it_process-=-null-check.patch
posix-timers-release_posix_timer-kill-the-bogus-put_task_struct-it_process.patch
signals-sigqueue_free-dont-free-sigqueue-if-it-is-queued.patch
signals-introduce-sigqueue_cancelled.patch
posix-timers-use-sigqueue_cancelled-when-the-timer-is-destroyed.patch
put_pid-make-sure-we-dont-free-the-live-pid.patch
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