Audit: add support to match lsm labels on user audit messages

Add support for matching by security label (e.g. SELinux context) of
the sender of an user-space audit record.

The audit filter code already allows user space to configure such
filters, but they were ignored during evaluation.  This patch implements
evaluation of these filters.

For example, after application of this patch, PAM authentication logs
caused by cron can be disabled using
	auditctl -a user,never -F subj_type=crond_t
Signed-off-by: Miloslav Trmac <mitr@redhat.com>
Acked-by: Eric Paris <eparis@redhat.com>
Signed-off-by: Al Viro <viro@zeniv.linux.org.uk>

kernel/auditfilter.c

@@ -1252,6 +1252,18 @@ static int audit_filter_user_rules(struct netlink_skb_parms *cb,
 		case AUDIT_LOGINUID:
 			result = audit_comparator(cb->loginuid, f->op, f->val);
 			break;
+		case AUDIT_SUBJ_USER:
+		case AUDIT_SUBJ_ROLE:
+		case AUDIT_SUBJ_TYPE:
+		case AUDIT_SUBJ_SEN:
+		case AUDIT_SUBJ_CLR:
+			if (f->lsm_rule)
+				result = security_audit_rule_match(cb->sid,
+								   f->type,
+								   f->op,
+								   f->lsm_rule,
+								   NULL);
+			break;
 		}
 
 		if (!result)