kcm: Only allow TCP sockets to be attached to a KCM mux

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+8865eaff7f9acd593945@syzkaller.appspotmail.com
Signed-off-by: Tom Herbert <tom@quantonium.net>
Reviewed-by: Eric Dumazet <edumazet@google.com>
Signed-off-by: David S. Miller <davem@davemloft.net>

diff --git a/net/kcm/kcmsock.c b/net/kcm/kcmsock.c
index d4e98f2..7632797 100644 (file)
--- a/net/kcm/kcmsock.c
+++ b/net/kcm/kcmsock.c
@@ -1387,8 +1387,13 @@ 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)
+       /* 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);