linux-kernel - [PATCH 1/1] signals: don't abuse __flush_signals() in selinux_bprm_committed

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Message-ID: <20150504164558.GB10118@redhat.com>
Date:	Mon, 4 May 2015 18:45:58 +0200
From:	Oleg Nesterov <oleg@...hat.com>
To:	Andrew Morton <akpm@...ux-foundation.org>,
	Ingo Molnar <mingo@...nel.org>
Cc:	Linus Torvalds <torvalds@...ux-foundation.org>,
	Neil Brown <neilb@...e.de>, Evgeniy Polyakov <zbr@...emap.net>,
	Stephen Smalley <sds@...ho.nsa.gov>,
	Alex Williamson <alex.williamson@...hat.com>,
	linux-kernel <linux-kernel@...r.kernel.org>,
	kvm <kvm@...r.kernel.org>, Paul Moore <paul@...l-moore.com>,
	Eric Paris <eparis@...isplace.org>
Subject: [PATCH 1/1] 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@...hat.com>
---
 include/linux/sched.h    |    1 -
 kernel/signal.c          |   13 ++++---------
 security/selinux/hooks.c |    6 ++++--
 3 files changed, 8 insertions(+), 12 deletions(-)

diff --git a/include/linux/sched.h b/include/linux/sched.h
index 8db31ef..eb1ac84 100644
--- a/include/linux/sched.h
+++ b/include/linux/sched.h
@@ -2345,7 +2345,6 @@ 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 16a3052..837ca7d 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 6da7532..6907d11 100644
--- a/security/selinux/hooks.c
+++ b/security/selinux/hooks.c
@@ -2397,10 +2397,12 @@ 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);
 	}
-- 
1.5.5.1


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