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

commit f991af3daa 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>
master
Cong Wang 4 years ago
committed by Greg Kroah-Hartman
parent
commit
e6952841ad
  1. 4
      ipc/mqueue.c

4
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;

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