[PATCH net-next 1/2] kcm: Only allow TCP sockets to be attached to a KCM mux

[Tom Herbert]

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

diff --git a/net/kcm/kcmsock.c b/net/kcm/kcmsock.c
index d4e98f20fc2a..474ea2200592 100644
--- a/net/kcm/kcmsock.c
+++ b/net/kcm/kcmsock.c
@@ -1391,6 +1391,15 @@ static int kcm_attach(struct socket *sock, struct socket 
*csock,
        if (csk->sk_family == PF_KCM)
                return -EOPNOTSUPP;
 
+       /* 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);
        if (!psock)
                return -ENOMEM;
-- 
2.11.0