From e6952841ade0f937750c7748a812cb403bd744b0 Mon Sep 17 00:00:00 2001 From: Cong Wang Date: Sun, 9 Jul 2017 13:19:55 -0700 Subject: [PATCH] mqueue: fix a use-after-free in sys_mq_notify() 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 Signed-off-by: Cong Wang Cc: Andrew Morton Cc: Manfred Spraul Signed-off-by: Linus Torvalds Signed-off-by: Greg Kroah-Hartman --- ipc/mqueue.c | 4 +++- 1 file changed, 3 insertions(+), 1 deletion(-) diff --git a/ipc/mqueue.c b/ipc/mqueue.c index 8cbd6e6894d5..28a142f1be36 100644 --- a/ipc/mqueue.c +++ b/ipc/mqueue.c @@ -1249,8 +1249,10 @@ 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; -- 2.20.1