net/tls: Only attach to sockets in ESTABLISHED state

Calling accept on a TCP socket with a TLS ulp attached results
in two sockets that share the same ulp context.
The ulp context is freed while a socket is destroyed, so
after one of the sockets is released, the second second will
trigger a use after free when it tries to access the ulp context
attached to it.
We restrict the TLS ulp to sockets in ESTABLISHED state
to prevent the scenario above.

Fixes: 3c4d7559 ("tls: kernel TLS support")
Reported-by: syzbot+904e7cd6c5c741609228@syzkaller.appspotmail.com
Signed-off-by: Ilya Lesokhin <ilyal@mellanox.com>
Signed-off-by: David S. Miller <davem@davemloft.net>

net/tls/tls_main.c

@@ -454,6 +454,15 @@ static int tls_init(struct sock *sk)
 	struct tls_context *ctx;
 	int rc = 0;
 
+	/* The TLS ulp is currently supported only for TCP sockets
+	 * in ESTABLISHED state.
+	 * Supporting sockets in LISTEN state will require us
+	 * to modify the accept implementation to clone rather then
+	 * share the ulp context.
+	 */
+	if (sk->sk_state != TCP_ESTABLISHED)
+		return -ENOTSUPP;
+
 	/* allocate tls context */
 	ctx = kzalloc(sizeof(*ctx), GFP_KERNEL);
 	if (!ctx) {