smack: recognize ipv4 CIPSO w/o categories

If SMACK label has CIPSO representation w/o categories, e.g.:

| # cat /smack/cipso2
| foo  10
| @ 250/2
| ...

then SMACK does not recognize such CIPSO in input ipv4 packets
and substitues '*' label instead. Audit records may look like

| lsm=SMACK fn=smack_socket_sock_rcv_skb action=denied
|   subject="*" object="_" requested=w pid=0 comm="swapper/1" ...

This happens in two steps:

1) security/smack/smackfs.c`smk_set_cipso
   does not clear NETLBL_SECATTR_MLS_CAT
   from (struct smack_known *)skp->smk_netlabel.flags
   on assigning CIPSO w/o categories:

| rcu_assign_pointer(skp->smk_netlabel.attr.mls.cat, ncats.attr.mls.cat);
| skp->smk_netlabel.attr.mls.lvl = ncats.attr.mls.lvl;

2) security/smack/smack_lsm.c`smack_from_secattr
   can not match skp->smk_netlabel with input packet's
   struct netlbl_lsm_secattr *sap
   because sap->flags have not NETLBL_SECATTR_MLS_CAT (what is correct)
   but skp->smk_netlabel.flags have (what is incorrect):

| if ((sap->flags & NETLBL_SECATTR_MLS_CAT) == 0) {
| 	if ((skp->smk_netlabel.flags &
| 		 NETLBL_SECATTR_MLS_CAT) == 0)
| 		found = 1;
| 	break;
| }

This commit sets/clears NETLBL_SECATTR_MLS_CAT in
skp->smk_netlabel.flags according to the presense of CIPSO categories.
The update of smk_netlabel is not atomic, so input packets processing
still may be incorrect during short time while update proceeds.

Signed-off-by: Konstantin Andreev <[email protected]>
Signed-off-by: Casey Schaufler <[email protected]>

security/smack/smackfs.c

@@ -906,6 +906,10 @@ static ssize_t smk_set_cipso(struct file *file, const char __user *buf,
 	if (rc >= 0) {
 		old_cat = skp->smk_netlabel.attr.mls.cat;
 		rcu_assign_pointer(skp->smk_netlabel.attr.mls.cat, ncats.attr.mls.cat);
+		if (ncats.attr.mls.cat)
+			skp->smk_netlabel.flags |= NETLBL_SECATTR_MLS_CAT;
+		else
+			skp->smk_netlabel.flags &= ~(u32)NETLBL_SECATTR_MLS_CAT;
 		skp->smk_netlabel.attr.mls.lvl = ncats.attr.mls.lvl;
 		synchronize_rcu();
 		netlbl_catmap_free(old_cat);