Patch "kcm: do not attach PF_KCM sockets to avoid deadlock" has been added to the 4.9-stable tree

This is a note to let you know that I've just added the patch titled

kcm: do not attach PF_KCM sockets to avoid deadlock

to the 4.9-stable tree which can be found at:
http://www.kernel.org/git/?p=linux/kernel/git/stable/stable-queue.git;a=summary

The filename of the patch is:
kcm-do-not-attach-pf_kcm-sockets-to-avoid-deadlock.patch
and it can be found in the queue-4.9 subdirectory.

If you, or anyone else, feels it should not be added to the stable tree, please let <[email protected]> know about it.

From: Eric Dumazet <[email protected]>
Date: Wed, 30 Aug 2017 09:29:31 -0700
Subject: kcm: do not attach PF_KCM sockets to avoid deadlock

From: Eric Dumazet <[email protected]>

[ Upstream commit 351050ecd6523374b370341cc29fe61e2201556b ]

syzkaller had no problem to trigger a deadlock, attaching a KCM socket to another one (or itself). (original syzkaller report was a very confusing lockdep splat during a sendmsg())

It seems KCM claims to only support TCP, but no enforcement is done, so we might need to add additional checks.

---
 net/kcm/kcmsock.c |    4 ++++
 1 file changed, 4 insertions(+)

@@ -1381,6 +1381,10 @@ static int kcm_attach(struct socket *soc
 	if (!csk)
 		return -EINVAL;
 
+	/* We must prevent loops or risk deadlock ! */
+	if (csk->sk_family == PF_KCM)
+		return -EOPNOTSUPP;
+
 	psock = kmem_cache_zalloc(kcm_psockp, GFP_KERNEL);
 	if (!psock)
 		return -ENOMEM;

Patches currently in stable-queue which might be from [email protected] are

queue-4.9/ipv6-fix-typo-in-fib6_net_exit.patch queue-4.9/ipv6-fix-sparse-warning-on-rt6i_node.patch queue-4.9/udp-on-peeking-bad-csum-drop-packets-even-if-not-at-head.patch queue-4.9/tcp-initialize-rcv_mss-to-tcp_min_mss-instead-of-0.patch queue-4.9/ipv6-add-rcu-grace-period-before-freeing-fib6_node.patch queue-4.9/kcm-do-not-attach-pf_kcm-sockets-to-avoid-deadlock.patch