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>

3 files changed, 8 insertions, 12 deletions

diff --git a/include/linux/sched.h b/include/linux/sched.h
index 8222ae4..4f84aad 100644
--- a/include/linux/sched.h
+++ b/include/linux/sched.h
@@ -2373,7 +2373,6 @@ extern void sched_dead(struct task_struct *p);
 
 extern void proc_caches_init(void);
 extern void flush_signals(struct task_struct *);
-extern void __flush_signals(struct task_struct *);
 extern void ignore_signals(struct task_struct *);
 extern void flush_signal_handlers(struct task_struct *, int force_default);
 extern int dequeue_signal(struct task_struct *tsk, sigset_t *mask, siginfo_t *info);
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);
 }
 
diff --git a/security/selinux/hooks.c b/security/selinux/hooks.c
index 99c4a00..8abbd54 100644
--- a/security/selinux/hooks.c
+++ b/security/selinux/hooks.c
@@ -2416,10 +2416,12 @@ static void selinux_bprm_committed_creds(struct linux_binprm *bprm)
 		for (i = 0; i < 3; i++)
 			do_setitimer(i, &itimer, NULL);
 		spin_lock_irq(&current->sighand->siglock);
-		if (!(current->signal->flags & SIGNAL_GROUP_EXIT)) {
-			__flush_signals(current);
+		if (!fatal_signal_pending(current)) {
+			flush_sigqueue(&current->pending);
+			flush_sigqueue(&current->signal->shared_pending);
 			flush_signal_handlers(current, 1);
 			sigemptyset(&current->blocked);
+			recalc_sigpending();
 		}
 		spin_unlock_irq(&current->sighand->siglock);
 	}