[PATCH v3 11/14] flow, fwd: Consult rules table when forwarding a new flow from socket

[David Gibson <david@gibson.dropbear.id.au>]

We now have a formal array of forwarding rules.  However, we don't actually
consult it when we forward a new flow.  Instead we rely on (a) implicit
information (we wouldn't be here if there wasn't a listening socket for the
rule) and (b) the legacy delta[] data structure.

Start addressing this, by searching for a matching forwarding rule when
attempting to forward a new flow.  For now this is incomplete:
 * We only do this for socket-initiated flows
 * We make a potentially costly linear lookup
 * We don't actually use the matching rule for anything yet

We'll address each of those in later patches.

Signed-off-by: David Gibson <david@gibson.dropbear.id.au>
---
 flow.c | 43 ++++++++++++++++++++++++++++++++++---------
 fwd.c  | 33 +++++++++++++++++++++++++++++++++
 fwd.h  |  2 ++
 3 files changed, 69 insertions(+), 9 deletions(-)

diff --git a/flow.c b/flow.c
index 4f534865..045e9712 100644
--- a/flow.c
+++ b/flow.c
@@ -489,7 +489,7 @@ struct flowside *flow_initiate_sa(union flow *flow, uint8_t pif,
 struct flowside *flow_target(const struct ctx *c, union flow *flow,
 			     uint8_t proto)
 {
-	char estr[INANY_ADDRSTRLEN], fstr[INANY_ADDRSTRLEN];
+	char estr[INANY_ADDRSTRLEN], ostr[INANY_ADDRSTRLEN];
 	struct flow_common *f = &flow->f;
 	const struct flowside *ini = &f->side[INISIDE];
 	struct flowside *tgt = &f->side[TGTSIDE];
@@ -500,6 +500,30 @@ struct flowside *flow_target(const struct ctx *c, union flow *flow,
 	ASSERT(f->pif[INISIDE] != PIF_NONE && f->pif[TGTSIDE] == PIF_NONE);
 	ASSERT(flow->f.state == FLOW_STATE_INI);
 
+	if (pif_is_socket(f->pif[INISIDE])) {
+		const struct fwd_ports *fwd;
+
+		if (f->pif[INISIDE] == PIF_HOST && proto == IPPROTO_TCP)
+			fwd = &c->tcp.fwd_in;
+		else if (f->pif[INISIDE] == PIF_HOST && proto == IPPROTO_UDP)
+			fwd = &c->udp.fwd_in;
+		else if (f->pif[INISIDE] == PIF_SPLICE && proto == IPPROTO_TCP)
+			fwd = &c->tcp.fwd_out;
+		else if (f->pif[INISIDE] == PIF_SPLICE && proto == IPPROTO_UDP)
+			fwd = &c->udp.fwd_out;
+		else
+			goto nofwd;
+
+		if (!fwd_rule_search(fwd, ini)) {
+			/* This shouldn't happen, because if there's no rule for
+			 * it we should have no listening socket that would let
+			 * us get here
+			 */
+			flow_dbg(flow, "Unexpected missing forward rule");
+			goto nofwd;
+		}
+	}
+
 	switch (f->pif[INISIDE]) {
 	case PIF_TAP:
 		memcpy(f->tap_omac, MAC_UNDEF, ETH_ALEN);
@@ -514,22 +538,23 @@ struct flowside *flow_target(const struct ctx *c, union flow *flow,
 		tgtpif = fwd_nat_from_host(c, proto, ini, tgt);
 		fwd_neigh_mac_get(c, &tgt->oaddr, f->tap_omac);
 		break;
-
 	default:
-		flow_err(flow, "No rules to forward %s [%s]:%hu -> [%s]:%hu",
-			 pif_name(f->pif[INISIDE]),
-			 inany_ntop(&ini->eaddr, estr, sizeof(estr)),
-			 ini->eport,
-			 inany_ntop(&ini->oaddr, fstr, sizeof(fstr)),
-			 ini->oport);
+		goto nofwd;
 	}
 
 	if (tgtpif == PIF_NONE)
-		return NULL;
+		goto nofwd;
 
 	f->pif[TGTSIDE] = tgtpif;
 	flow_set_state(f, FLOW_STATE_TGT);
 	return tgt;
+
+nofwd:
+	flow_err(flow, "No rules to forward %s %s [%s]:%hu -> [%s]:%hu",
+		 pif_name(f->pif[INISIDE]), ipproto_name(proto),
+		 inany_ntop(&ini->eaddr, estr, sizeof(estr)), ini->eport,
+		 inany_ntop(&ini->oaddr, ostr, sizeof(ostr)), ini->oport);
+	return NULL;
 }
 
 /**
diff --git a/fwd.c b/fwd.c
index 3f088fd2..633ba5db 100644
--- a/fwd.c
+++ b/fwd.c
@@ -409,6 +409,39 @@ void fwd_rule_add(struct fwd_ports *fwd, uint8_t flags,
 	}
 }
 
+/**
+ * fwd_rule_match() - Does a prospective flow match a given forwarding rule
+ * @rule:	Forwarding rule
+ * @ini:	Initiating side flow information
+ *
+ * Returns: true if the rule applies to the flow, false otherwise
+ */
+static bool fwd_rule_match(const struct fwd_rule *rule,
+			   const struct flowside *ini)
+{
+	return inany_matches(&ini->oaddr, fwd_rule_addr(rule)) &&
+		ini->oport >= rule->first && ini->oport <= rule->last;
+}
+
+/**
+ * fwd_rule_search() - Find a rule which matches a prospective flow
+ * @fwd:	Forwarding table
+ * @ini:	Initiating side flow information
+ *
+ * Returns: first matching rule, or NULL if there is none
+ */
+const struct fwd_rule *fwd_rule_search(const struct fwd_ports *fwd,
+				       const struct flowside *ini)
+{
+	unsigned i;
+
+	for (i = 0; i < fwd->count; i++) {
+		if (fwd_rule_match(&fwd->rules[i], ini))
+			return &fwd->rules[i];
+	}
+	return NULL;
+}
+
 /**
  * fwd_rules_print() - Print forwarding rules for debugging
  * @fwd:	Table to print
diff --git a/fwd.h b/fwd.h
index f84e7c01..a10bdbb4 100644
--- a/fwd.h
+++ b/fwd.h
@@ -103,6 +103,8 @@ struct fwd_ports {
 void fwd_rule_add(struct fwd_ports *fwd, uint8_t flags,
 		  const union inany_addr *addr, const char *ifname,
 		  in_port_t first, in_port_t last, in_port_t to);
+const struct fwd_rule *fwd_rule_search(const struct fwd_ports *fwd,
+				       const struct flowside *ini);
 void fwd_rules_print(const struct fwd_ports *fwd);
 
 void fwd_scan_ports_init(struct ctx *c);
-- 
2.52.0