[MLSXFRM]: Add security sid to sock

This adds security for IP sockets at the sock level. Security at the
sock level is needed to enforce the SELinux security policy for
security associations even when a sock is orphaned (such as in the TCP
LAST_ACK state).

This will also be used to enforce SELinux controls over data arriving
at or leaving a child socket while it's still waiting to be accepted.

Signed-off-by: Venkat Yekkirala <vyekkirala@TrustedCS.com>
Signed-off-by: David S. Miller <davem@davemloft.net>

security/selinux/include/objsec.h

@@ -99,6 +99,7 @@ struct netif_security_struct {
 
 struct sk_security_struct {
 	struct sock *sk;		/* back pointer to sk object */
+	u32 sid;			/* SID of this object */
 	u32 peer_sid;			/* SID of peer */
 };