linux-kernel - [PATCH 4.4 30/57] mqueue: fix a use-after-free in sys_mq

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Message-Id: <20170713153959.746019711@linuxfoundation.org>
Date:   Thu, 13 Jul 2017 17:42:45 +0200
From:   Greg Kroah-Hartman <gregkh@...uxfoundation.org>
To:     linux-kernel@...r.kernel.org
Cc:     Greg Kroah-Hartman <gregkh@...uxfoundation.org>,
        stable@...r.kernel.org, GeneBlue <geneblue.mail@...il.com>,
        Cong Wang <xiyou.wangcong@...il.com>,
        Andrew Morton <akpm@...ux-foundation.org>,
        Manfred Spraul <manfred@...orfullife.com>,
        Linus Torvalds <torvalds@...ux-foundation.org>
Subject: [PATCH 4.4 30/57] mqueue: fix a use-after-free in sys_mq_notify()

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

------------------

From: Cong Wang <xiyou.wangcong@...il.com>

commit f991af3daabaecff34684fd51fac80319d1baad1 upstream.

The retry logic for netlink_attachskb() inside sys_mq_notify()
is nasty and vulnerable:

1) The sock refcnt is already released when retry is needed
2) The fd is controllable by user-space because we already
   release the file refcnt

so we when retry but the fd has been just closed by user-space
during this small window, we end up calling netlink_detachskb()
on the error path which releases the sock again, later when
the user-space closes this socket a use-after-free could be
triggered.

Setting 'sock' to NULL here should be sufficient to fix it.

Reported-by: GeneBlue <geneblue.mail@...il.com>
Signed-off-by: Cong Wang <xiyou.wangcong@...il.com>
Cc: Andrew Morton <akpm@...ux-foundation.org>
Cc: Manfred Spraul <manfred@...orfullife.com>
Signed-off-by: Linus Torvalds <torvalds@...ux-foundation.org>
Signed-off-by: Greg Kroah-Hartman <gregkh@...uxfoundation.org>

---
 ipc/mqueue.c |    4 +++-
 1 file changed, 3 insertions(+), 1 deletion(-)

--- a/ipc/mqueue.c
+++ b/ipc/mqueue.c
@@ -1251,8 +1251,10 @@ retry:
 
 			timeo = MAX_SCHEDULE_TIMEOUT;
 			ret = netlink_attachskb(sock, nc, &timeo, NULL);
-			if (ret == 1)
+			if (ret == 1) {
+				sock = NULL;
 				goto retry;
+			}
 			if (ret) {
 				sock = NULL;
 				nc = NULL;