4.14-stable review patch.  If anyone has any objections, please let me know.

------------------

From: Tom Herbert <t...@quantonium.net>

commit 581e7226a5d43f629eb6399a121f85f6a15f81be upstream.

TCP sockets for IPv4 and IPv6 that are not listeners or in closed
stated are allowed to be attached to a KCM mux.

Fixes: ab7ac4eb9832 ("kcm: Kernel Connection Multiplexor module")
Reported-by: syzbot+8865eaff7f9acd593...@syzkaller.appspotmail.com
Signed-off-by: Tom Herbert <t...@quantonium.net>
Reviewed-by: Eric Dumazet <eduma...@google.com>
Signed-off-by: David S. Miller <da...@davemloft.net>
Signed-off-by: Greg Kroah-Hartman <gre...@linuxfoundation.org>

---
 net/kcm/kcmsock.c |    9 +++++++--
 1 file changed, 7 insertions(+), 2 deletions(-)

--- a/net/kcm/kcmsock.c
+++ b/net/kcm/kcmsock.c
@@ -1387,8 +1387,13 @@ static int kcm_attach(struct socket *soc
        if (!csk)
                return -EINVAL;
 
-       /* We must prevent loops or risk deadlock ! */
-       if (csk->sk_family == PF_KCM)
+       /* Only allow TCP sockets to be attached for now */
+       if ((csk->sk_family != AF_INET && csk->sk_family != AF_INET6) ||
+           csk->sk_protocol != IPPROTO_TCP)
+               return -EOPNOTSUPP;
+
+       /* Don't allow listeners or closed sockets */
+       if (csk->sk_state == TCP_LISTEN || csk->sk_state == TCP_CLOSE)
                return -EOPNOTSUPP;
 
        psock = kmem_cache_zalloc(kcm_psockp, GFP_KERNEL);


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