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.

[akpm@linux-foundation.org: remove uneeded BUG_ON()]
Signed-off-by: Ahmed S. Darwish <darwish.07@gmail.com>
Acked-by: Casey Schaufler <casey@schuafler-ca.com>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>

security/smack/smack_lsm.c

@@ -701,7 +701,7 @@ static int smack_inode_getsecurity(const struct inode *inode,
 		return -EOPNOTSUPP;
 
 	sock = SOCKET_I(ip);
-	if (sock == NULL)
+	if (sock == NULL || sock->sk == NULL)
 		return -EOPNOTSUPP;
 
 	ssp = sock->sk->sk_security;
@@ -1280,10 +1280,11 @@ static void smack_to_secattr(char *smack, struct netlbl_lsm_secattr *nlsp)
  */
 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)
@@ -1331,7 +1332,7 @@ static int smack_inode_setsecurity(struct inode *inode, const char *name,
 		return -EOPNOTSUPP;
 
 	sock = SOCKET_I(inode);
-	if (sock == NULL)
+	if (sock == NULL || sock->sk == NULL)
 		return -EOPNOTSUPP;
 
 	ssp = sock->sk->sk_security;
@@ -1362,7 +1363,7 @@ static int smack_inode_setsecurity(struct inode *inode, const char *name,
 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.