From: Eric Dumazet <edumazet@google.com>
Date: Wed, 30 Aug 2017 09:29:31 -0700
Subject: [PATCH] kcm: do not attach PF_KCM sockets to avoid deadlock
References: bnc#1060662
Patch-mainline: v4.12.14
Git-commit: 351050ecd6523374b370341cc29fe61e2201556b

[ 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.

Fixes: ab7ac4eb9832 ("kcm: Kernel Connection Multiplexor module")
Signed-off-by: Eric Dumazet <edumazet@google.com>
Reported-by: Dmitry Vyukov <dvyukov@google.com>
Acked-by: Tom Herbert <tom@quantonium.net>
Signed-off-by: David S. Miller <davem@davemloft.net>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>
Signed-off-by: Jiri Slaby <jslaby@suse.cz>
---
 net/kcm/kcmsock.c | 4 ++++
 1 file changed, 4 insertions(+)

diff --git a/net/kcm/kcmsock.c b/net/kcm/kcmsock.c
index deca20fb2ce2..0ddcb209bea6 100644
--- a/net/kcm/kcmsock.c
+++ b/net/kcm/kcmsock.c
@@ -1383,6 +1383,10 @@ static int kcm_attach(struct socket *sock, struct socket *csock,
 	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;
-- 
2.14.2