nfc: Avoid endless loops caused by repeated llcp_sock_connect()

When sock_wait_state() returns -EINPROGRESS, "sk->sk_state" is
 LLCP_CONNECTING. In this case, llcp_sock_connect() is repeatedly invoked,
 nfc_llcp_sock_link() will add sk to local->connecting_sockets twice.
 sk->sk_node->next will point to itself, that will make an endless loop
 and hang-up the system.
To fix it, check whether sk->sk_state is LLCP_CONNECTING in
 llcp_sock_connect() to avoid repeated invoking.

Fixes: b4011239 ("NFC: llcp: Fix non blocking sockets connections")
Reported-by: "kiyin(尹亮)" <kiyin@tencent.com>
Link: https://www.openwall.com/lists/oss-security/2020/11/01/1
Cc: <stable@vger.kernel.org> #v3.11
Signed-off-by: Xiaoming Ni <nixiaoming@huawei.com>
Signed-off-by: David S. Miller <davem@davemloft.net>

net/nfc/llcp_sock.c

@@ -673,6 +673,10 @@ static int llcp_sock_connect(struct socket *sock, struct sockaddr *_addr,
 		ret = -EISCONN;
 		goto error;
 	}
+	if (sk->sk_state == LLCP_CONNECTING) {
+		ret = -EINPROGRESS;
+		goto error;
+	}
 
 	dev = nfc_get_device(addr->dev_idx);
 	if (dev == NULL) {