tree 6285620a3d1b7d676e9ce367a6d9cfac05a30045
parent c48f76d680ad9ad443290ce0f1e8f92db6986bf5
author Cong Wang <xiyou.wangcong@gmail.com> 1499631595 -0700
committer Greg Kroah-Hartman <gregkh@linuxfoundation.org> 1500113770 +0200

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 <geneblue.mail@gmail.com>
Signed-off-by: Cong Wang <xiyou.wangcong@gmail.com>
Cc: Andrew Morton <akpm@linux-foundation.org>
Cc: Manfred Spraul <manfred@colorfullife.com>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>