Re: [PATCH v2 3/8] flow: add mac address of LAN local remote hosts to flow

On Thu, 12 Jun 2025 00:21:47 -0400 Jon Maloy wrote:

When communicating with remote hosts on the local network, some guest applications want to see the real mac address of that host instead of passt/pasta's own tap address. The flowside structure is a convenient location for storing that address, so we do that in this commit.

Note that we don´t add usage of this address in this commit, - that will come in later commits.

Signed-off-by: Jon Maloy --- flow.c | 13 ++++++++++++- flow.h | 2 ++ 2 files changed, 14 insertions(+), 1 deletion(-)

diff --git a/flow.c b/flow.c index da5c813..fffc817 100644 --- a/flow.c +++ b/flow.c @@ -20,6 +20,7 @@ #include "flow.h" #include "flow_table.h" #include "repair.h" +#include "netlink.h"

const char *flow_state_str[] = { [FLOW_STATE_FREE] = "FREE", @@ -438,7 +439,7 @@ struct flowside *flow_target(const struct ctx *c, union flow *flow, { char estr[INANY_ADDRSTRLEN], fstr[INANY_ADDRSTRLEN]; struct flow_common *f = &flow->f; - const struct flowside *ini = &f->side[INISIDE]; + struct flowside *ini = &f->side[INISIDE]; struct flowside *tgt = &f->side[TGTSIDE]; uint8_t tgtpif = PIF_NONE;

@@ -446,10 +447,16 @@ struct flowside *flow_target(const struct ctx *c, union flow *flow, ASSERT(f->type == FLOW_TYPE_NONE); ASSERT(f->pif[INISIDE] != PIF_NONE && f->pif[TGTSIDE] == PIF_NONE); ASSERT(flow->f.state == FLOW_STATE_INI); + memcpy(ini->mac, c->our_tap_mac, ETH_ALEN); + memcpy(tgt->mac, c->our_tap_mac, ETH_ALEN);

switch (f->pif[INISIDE]) { case PIF_TAP: tgtpif = fwd_nat_from_tap(c, proto, ini, tgt); + + /* If remote host on local network - insert its mac address */ + if (!memcmp(&tgt->eaddr, &ini->oaddr, sizeof(ini->oaddr))) + nl_mac_get(nl_sock, &ini->oaddr, ini->mac); break;

case PIF_SPLICE: @@ -458,6 +465,10 @@ struct flowside *flow_target(const struct ctx *c, union flow *flow,

case PIF_HOST: tgtpif = fwd_nat_from_host(c, proto, ini, tgt); + + /* If remote host on local network - insert its mac address */ + if (!memcmp(&tgt->oaddr, &ini->eaddr, sizeof(ini->eaddr))) + nl_mac_get(nl_sock, &tgt->oaddr, tgt->mac); break;

default: diff --git a/flow.h b/flow.h index cac618a..916951b 100644 --- a/flow.h +++ b/flow.h @@ -143,12 +143,14 @@ extern const uint8_t flow_proto[]; * @oaddr: Our address (local address from passt's PoV) * @eport: Endpoint port * @oport: Our port + * @mac: MAC address of remote endpoint */ struct flowside { union inany_addr oaddr; union inany_addr eaddr; in_port_t oport; in_port_t eport; + unsigned char mac[6];

We'll never have two MAC addresses that are not c->our_tap_mac in a single flow, right? If that's the case, shouldn't we move this to flow_common, so that we have just one instance, reflecting our usage?

};

/**

-- Stefano