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

Silly nits only and a couple of remarks that will probably be clarified at a later point: On Thu, 8 Jan 2026 13:29:45 +1100 David Gibson wrote:

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 --- 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);

This assumes we're still using this function for inbound forwards only (eaddr / eport -> oaddr / oport), perhaps we'll want a macro once it starts being used for the other way around as well (if at all). By the way, for rules, earlier in this series, you used "=>" to separate source and target of the forward, here it's still "->", I guess we should settle on one version (it just occurred to me while testing stuff: it might be useful to grep in logs).

+ 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

Does [...]?

+ * @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;

The usual alignment is: 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

I guess that this will eventually need to become a function matching the most specific rule first, tie breakers could be: 1. specific address given vs. wildcard 2. specific interface given vs. no interface 3. the day we support/need it: specific port/range vs. no port 4. smallest port range 5. the day we support/need something like this: longest prefix length and after this we should actually have an error on insertion (already guaranteed I think).

+ */ +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]; + }

Extra newline here to clearly separate the two outcomes.

+ 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);

-- Stefano