SELinux: Don't flush inherited SIGKILL during execve()

Don't flush inherited SIGKILL during execve() in SELinux's post cred commit
hook.  This isn't really a security problem: if the SIGKILL came before the
credentials were changed, then we were right to receive it at the time, and
should honour it; if it came after the creds were changed, then we definitely
should honour it; and in any case, all that will happen is that the process
will be scrapped before it ever returns to userspace.

Signed-off-by: David Howells <dhowells@redhat.com>
Signed-off-by: Oleg Nesterov <oleg@redhat.com>
Signed-off-by: James Morris <jmorris@namei.org>

3 files changed, 14 insertions, 7 deletions

diff --git a/include/linux/sched.h b/include/linux/sched.h
index 1d19c025f9d2..d3b787c7aef3 100644
--- a/include/linux/sched.h
+++ b/include/linux/sched.h
@@ -1875,6 +1875,7 @@ 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 1c8814481a11..f93efec14ff5 100644
--- a/kernel/signal.c
+++ b/kernel/signal.c
@@ -238,14 +238,19 @@ void flush_sigqueue(struct sigpending *queue)
 /*
  * Flush all pending signals for a task.
  */
+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);
-	clear_tsk_thread_flag(t, TIF_SIGPENDING);
-	flush_sigqueue(&t->pending);
-	flush_sigqueue(&t->signal->shared_pending);
+	__flush_signals(t);
 	spin_unlock_irqrestore(&t->sighand->siglock, flags);
 }
 
diff --git a/security/selinux/hooks.c b/security/selinux/hooks.c
index dd19ba81201f..5a345115036c 100644
--- a/security/selinux/hooks.c
+++ b/security/selinux/hooks.c
@@ -2394,11 +2394,12 @@ static void selinux_bprm_committed_creds(struct linux_binprm *bprm)
 		memset(&itimer, 0, sizeof itimer);
 		for (i = 0; i < 3; i++)
 			do_setitimer(i, &itimer, NULL);
-		flush_signals(current);
 		spin_lock_irq(&current->sighand->siglock);
-		flush_signal_handlers(current, 1);
-		sigemptyset(&current->blocked);
-		recalc_sigpending();
+		if (!(current->signal->flags & SIGNAL_GROUP_EXIT)) {
+			__flush_signals(current);
+			flush_signal_handlers(current, 1);
+			sigemptyset(&current->blocked);
+		}
 		spin_unlock_irq(&current->sighand->siglock);
 	}