linux-kernel - [PATCH 3.12 006/142] futex: Unlock hb->lock in futex_wait_requeue

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Date:	Fri, 26 Sep 2014 11:43:37 +0200
From:	Jiri Slaby <jslaby@...e.cz>
To:	stable@...r.kernel.org
Cc:	linux-kernel@...r.kernel.org, Thomas Gleixner <tglx@...utronix.de>,
	Peter Zijlstra <a.p.zijlstra@...llo.nl>,
	Jiri Slaby <jslaby@...e.cz>
Subject: [PATCH 3.12 006/142] futex: Unlock hb->lock in futex_wait_requeue_pi() error path

From: Thomas Gleixner <tglx@...utronix.de>

3.12-stable review patch.  If anyone has any objections, please let me know.

===============

commit 13c42c2f43b19aab3195f2d357db00d1e885eaa8 upstream.

futex_wait_requeue_pi() calls futex_wait_setup(). If
futex_wait_setup() succeeds it returns with hb->lock held and
preemption disabled. Now the sanity check after this does:

        if (match_futex(&q.key, &key2)) {
	   	ret = -EINVAL;
		goto out_put_keys;
	}

which releases the keys but does not release hb->lock.

So we happily return to user space with hb->lock held and therefor
preemption disabled.

Unlock hb->lock before taking the exit route.

Reported-by: Dave "Trinity" Jones <davej@...hat.com>
Signed-off-by: Thomas Gleixner <tglx@...utronix.de>
Reviewed-by: Darren Hart <dvhart@...ux.intel.com>
Reviewed-by: Davidlohr Bueso <dave@...olabs.net>
Cc: Peter Zijlstra <a.p.zijlstra@...llo.nl>
Cc: stable@...r.kernel.org
Link: http://lkml.kernel.org/r/alpine.DEB.2.10.1409112318500.4178@nanos
Signed-off-by: Thomas Gleixner <tglx@...utronix.de>
Signed-off-by: Jiri Slaby <jslaby@...e.cz>
---
 kernel/futex.c | 1 +
 1 file changed, 1 insertion(+)

diff --git a/kernel/futex.c b/kernel/futex.c
index f94695c9d38b..e4b9b60e25b1 100644
--- a/kernel/futex.c
+++ b/kernel/futex.c
@@ -2465,6 +2465,7 @@ static int futex_wait_requeue_pi(u32 __user *uaddr, unsigned int flags,
 	 * shared futexes. We need to compare the keys:
 	 */
 	if (match_futex(&q.key, &key2)) {
+		queue_unlock(&q, hb);
 		ret = -EINVAL;
 		goto out_put_keys;
 	}
-- 
2.1.0

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