netlabel: Fix NULL pointer exception caused by CALIPSO on IPv4 sockets

In the Linux kernel, the following vulnerability has been resolved: netlabel: Fix NULL pointer exception caused by CALIPSO on IPv4 sockets When calling netlbl_conn_setattr(), addr->sa_family is used to determine the function behavior. If sk is an IPv4 socket, but the connect function is called with an IPv6 address, the function calipso_sock_setattr() is triggered. Inside this function, the following code is executed: sk_fullsock(__sk) ? inet_sk(__sk)->pinet6 : NULL; Since sk is an IPv4 socket, pinet6 is NULL, leading to a null pointer dereference. This patch fixes the issue by checking if inet6_sk(sk) returns a NULL pointer before accessing pinet6.