4.4-stable review patch. If anyone has any objections, please let me know.
------------------
From: Cong Wang <xiyou.wangcong@xxxxxxxxx>
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@xxxxxxxxx>
Signed-off-by: Cong Wang <xiyou.wangcong@xxxxxxxxx>
Cc: Andrew Morton <akpm@xxxxxxxxxxxxxxxxxxxx>
Cc: Manfred Spraul <manfred@xxxxxxxxxxxxxxxx>
Signed-off-by: Linus Torvalds <torvalds@xxxxxxxxxxxxxxxxxxxx>
Signed-off-by: Greg Kroah-Hartman <gregkh@xxxxxxxxxxxxxxxxxxx>
---
ipc/mqueue.c | 4 +++-
1 file changed, 3 insertions(+), 1 deletion(-)
--- a/ipc/mqueue.c
+++ b/ipc/mqueue.c
@@ -1251,8 +1251,10 @@ 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;