From: Eric Dumazet <edumazet@google.com>
Date: Wed, 30 Aug 2017 16:29:31 +0000 (-0700)
Subject: kcm: do not attach PF_KCM sockets to avoid deadlock
X-Git-Tag: v4.13~9^2~7
X-Git-Url: https://git.karo-electronics.de/?p=karo-tx-linux.git;a=commitdiff_plain;h=351050ecd6523374b370341cc29fe61e2201556b

kcm: do not attach PF_KCM sockets to avoid deadlock

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>
---

diff --git a/net/kcm/kcmsock.c b/net/kcm/kcmsock.c
index da49191f7ad0..4abf6287d7e1 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;