mqueue: fix a use-after-free in sys_mq_notify()
[ Upstream commit f991af3d ] 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> Cc: stable@kernel.org Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org> Signed-off-by: Sasha Levin <alexander.levin@verizon.com>
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