Smack: check for 'struct socket' with NULL sk

There's a small problem with smack and NFS. A similar report was also
sent here: http://lkml.org/lkml/2007/10/27/85

I've also added similar checks in inode_{get/set}security(). Cheating from
SELinux post_create_socket(), it does the same.

[[e-mail]: remove uneeded BUG_ON()]
Signed-off-by: Ahmed S. Darwish <[e-mail]>
Acked-by: Casey Schaufler <[e-mail]>
Signed-off-by: Andrew Morton <[e-mail]>
Signed-off-by: Linus Torvalds <[e-mail]>

security/smack/smack_lsm.c

···
 		return -EOPNOTSUPP;
 
 	sock = SOCKET_I(ip);
-	if (sock == NULL)
+	if (sock == NULL || sock->sk == NULL)
 		return -EOPNOTSUPP;
 
 	ssp = sock->sk->sk_security;
···
  */
 static int smack_netlabel(struct sock *sk)
 {
-	struct socket_smack *ssp = sk->sk_security;
+	struct socket_smack *ssp;
 	struct netlbl_lsm_secattr secattr;
 	int rc = 0;
 
+	ssp = sk->sk_security;
 	netlbl_secattr_init(&secattr);
 	smack_to_secattr(ssp->smk_out, &secattr);
 	if (secattr.flags != NETLBL_SECATTR_NONE)
···
 		return -EOPNOTSUPP;
 
 	sock = SOCKET_I(inode);
-	if (sock == NULL)
+	if (sock == NULL || sock->sk == NULL)
 		return -EOPNOTSUPP;
 
 	ssp = sock->sk->sk_security;
···
 static int smack_socket_post_create(struct socket *sock, int family,
 				    int type, int protocol, int kern)
 {
-	if (family != PF_INET)
+	if (family != PF_INET || sock->sk == NULL)
 		return 0;
 	/*
 	 * Set the outbound netlbl.