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mqueue: fix a use-after-free in sys_mq_notify()

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

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 <>
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congwang authored and torvalds committed Jul 9, 2017
1 parent 2b97620 commit f991af3daabaecff34684fd51fac80319d1baad1
Showing with 3 additions and 1 deletion.
  1. +3 −1 ipc/mqueue.c
@@ -1270,8 +1270,10 @@ static int do_mq_notify(mqd_t mqdes, const struct sigevent *notification)

ret = netlink_attachskb(sock, nc, &timeo, NULL);
if (ret == 1)
if (ret == 1) {
sock = NULL;
goto retry;
if (ret) {
sock = NULL;
nc = NULL;

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commented on f991af3 Jun 8, 2018


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