signals: don't abuse __flush_signals() in selinux_bprm_committed_creds()

selinux_bprm_committed_creds()->__flush_signals() is not right, we
shouldn't clear TIF_SIGPENDING unconditionally. There can be other
reasons for signal_pending(): freezing(), JOBCTL_PENDING_MASK, and
potentially more.

Also change this code to check fatal_signal_pending() rather than
SIGNAL_GROUP_EXIT, it looks a bit better.

Now we can kill __flush_signals() before it finds another buggy user.

Note: this code looks racy, we can flush a signal which was sent after
the task SID has been updated.

Signed-off-by: Oleg Nesterov <oleg@redhat.com>
Signed-off-by: Paul Moore <pmoore@redhat.com>

1 files changed, 4 insertions, 9 deletions

diff --git a/kernel/signal.c b/kernel/signal.c
index d51c5dd..d497250 100644
--- a/kernel/signal.c
+++ b/kernel/signal.c
@@ -414,21 +414,16 @@ void flush_sigqueue(struct sigpending *queue)
 }
 
 /*
- * Flush all pending signals for a task.
+ * Flush all pending signals for this kthread.
  */
-void __flush_signals(struct task_struct *t)
-{
-	clear_tsk_thread_flag(t, TIF_SIGPENDING);
-	flush_sigqueue(&t->pending);
-	flush_sigqueue(&t->signal->shared_pending);
-}
-
 void flush_signals(struct task_struct *t)
 {
 	unsigned long flags;
 
 	spin_lock_irqsave(&t->sighand->siglock, flags);
-	__flush_signals(t);
+	clear_tsk_thread_flag(t, TIF_SIGPENDING);
+	flush_sigqueue(&t->pending);
+	flush_sigqueue(&t->signal->shared_pending);
 	spin_unlock_irqrestore(&t->sighand->siglock, flags);
 }