UPSTREAM: 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 <>
Signed-off-by: Andrey Ulanov <>

(cherry-picked from commit f991af3daabaecff34684fd51fac80319d1baad1)

TEST=kernel compiles

Change-Id: I402633e3308eb80c40ae881b13b2353eece0db8b
Commit-Ready: Andrey Ulanov <>
Tested-by: Andrey Ulanov <>
Reviewed-by: Guenter Roeck <>
(cherry picked from commit 1ae3ecacc8e915b702ee85a29935a1e4594e2582)
Commit-Queue: Andrey Ulanov <>
1 file changed