pf: Rationalize the ip_divert_ptr test

If a rule has a divert port set, then we can reasonably predict that
ipdivert.ko is loaded, and in particular that ip_divert_ptr is set.

Moreover, in this case, if ipdivert.ko is not loaded we should just drop
the packet instead of ignoring the divert rule.

Reviewed by:	igoro, kp, glebius
MFC after:	2 weeks
Sponsored by:	OPNsense
Sponsored by:	Klara, Inc.
Differential Revision:	https://reviews.freebsd.org/D54845

sys/netpfil/pf/pf.c

@@ -11961,11 +11961,11 @@ pf_test(sa_family_t af, int dir, int pflags, struct ifnet *ifp, struct mbuf **m0
 	    pf_is_loopback(af, pd.dst))
 		pd.m->m_flags |= M_SKIP_FIREWALL;
 
-	if (af == AF_INET && __predict_false(ip_divert_ptr != NULL) &&
-	    action == PF_PASS && r->divert.port && !PACKET_LOOPED(&pd)) {
+	if (af == AF_INET && action == PF_PASS && r->divert.port &&
+	    !PACKET_LOOPED(&pd)) {
 		mtag = m_tag_alloc(MTAG_PF_DIVERT, 0,
 		    sizeof(struct pf_divert_mtag), M_NOWAIT | M_ZERO);
-		if (mtag != NULL) {
+		if (__predict_true(mtag != NULL && ip_divert_ptr != NULL)) {
 			((struct pf_divert_mtag *)(mtag+1))->port =
 			    ntohs(r->divert.port);
 			((struct pf_divert_mtag *)(mtag+1))->idir =
@@ -11994,15 +11994,20 @@ pf_test(sa_family_t af, int dir, int pflags, struct ifnet *ifp, struct mbuf **m0
 			}
 			ip_divert_ptr(*m0, dir == PF_IN);
 			*m0 = NULL;
-
 			return (action);
-		} else {
+		} else if (mtag == NULL) {
 			/* XXX: ipfw has the same behaviour! */
 			action = PF_DROP;
 			REASON_SET(&reason, PFRES_MEMORY);
 			pd.act.log = PF_LOG_FORCE;
 			DPFPRINTF(PF_DEBUG_MISC,
 			    "pf: failed to allocate divert tag");
+		} else {
+			action = PF_DROP;
+			REASON_SET(&reason, PFRES_MATCH);
+			pd.act.log = PF_LOG_FORCE;
+			DPFPRINTF(PF_DEBUG_MISC,
+			    "pf: divert(4) is not loaded");
 		}
 	}
 	/* XXX: Anybody working on it?! */