From mboxrd@z Thu Jan 1 00:00:00 1970 From: Cong Wang Subject: [Patch v2] mqueue: fix a use-after-free in sys_mq_notify() Date: Sun, 9 Jul 2017 13:19:55 -0700 Message-ID: <1499631595-12625-1-git-send-email-xiyou.wangcong@gmail.com> Cc: linux-kernel@vger.kernel.org, geneblue.mail@gmail.com, Cong Wang , Andrew Morton , Linus Torvalds , Manfred Spraul To: netdev@vger.kernel.org Return-path: Sender: linux-kernel-owner@vger.kernel.org List-Id: netdev.vger.kernel.org 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 Cc: Andrew Morton Cc: Linus Torvalds Cc: Manfred Spraul Signed-off-by: Cong Wang --- ipc/mqueue.c | 4 +++- 1 file changed, 3 insertions(+), 1 deletion(-) diff --git a/ipc/mqueue.c b/ipc/mqueue.c index c9ff943..eb1391b 100644 --- a/ipc/mqueue.c +++ b/ipc/mqueue.c @@ -1270,8 +1270,10 @@ static int do_mq_notify(mqd_t mqdes, const struct sigevent *notification) 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; -- 2.5.5