On Fri, Sep 05, 2025 at 10:11:48PM -0400, Jon Maloy wrote:
When we receive an ARP request or NDP neigbor solicitation over the tap interface for a host on the local network segment attached to the template interface, we respond with that host's real MAC address.
Signed-off-by: Jon Maloy
LGTM, apart from small nits.
--- v3: - Added helper function to find out if a remote ip address is subject to NAT. This filters out local host addresses which should be presented with the passt/pasta local MAC address 9a:55:9a:55:9a:55 even though it is on the local segment. - Adapted to the change in nl_mac_get() function, so that we now consider only the template interface when checking the ARP/NDP table. v4: - Moved NAT check into the function nat_outbound() to obtain more precise criteria for when NAT is used. We may in theory have NAT even if original and translated addresses are equal, and we want to catch this case. - I chose to keep the wrapper funtion inany_nat(), but moved it to fwd.h/fwd.c and renamed it to fwd_inany_nat(). v5: - Simplified criteria for when we do ARP/NDP lookup. Now, we just try with the potentially translated address after an attempted NAT check. - Using the new ARP/NDP cache table instead of using netlink directly. --- arp.c | 9 ++++++++- fwd.c | 5 +++-- fwd.h | 2 ++ inany.c | 1 + ndp.c | 8 ++++++++ 5 files changed, 22 insertions(+), 3 deletions(-)
diff --git a/arp.c b/arp.c index 44677ad..8bff505 100644 --- a/arp.c +++ b/arp.c @@ -69,6 +69,7 @@ static bool ignore_arp(const struct ctx *c, */ int arp(const struct ctx *c, struct iov_tail *data) { + union inany_addr tgt, tgt_nat; struct { struct ethhdr eh; struct arphdr ah; @@ -80,6 +81,7 @@ int arp(const struct ctx *c, struct iov_tail *data) const struct ethhdr *eh; const struct arphdr *ah; const struct arpmsg *am; + uint8_t omac[ETH_ALEN];
Maybe tap_omac to disambiguate. Or else put it straight into resp.am.sha, similar to how you do for IPv6.
eh = IOV_REMOVE_HEADER(data, eh_storage); ah = IOV_REMOVE_HEADER(data, ah_storage); @@ -102,8 +104,13 @@ int arp(const struct ctx *c, struct iov_tail *data) resp.ah.ar_hln = ah->ar_hln; resp.ah.ar_pln = ah->ar_pln;
+ /* MAC address to return */ + inany_from_af(&tgt, AF_INET, am->tip); + nat_outbound(c, &tgt, &tgt_nat); + fwd_neigh_mac_get(c, &tgt_nat, omac); + /* ARP message */ - memcpy(resp.am.sha, c->our_tap_mac, sizeof(resp.am.sha)); + memcpy(resp.am.sha, omac, sizeof(resp.am.sha)); memcpy(resp.am.sip, am->tip, sizeof(resp.am.sip)); memcpy(resp.am.tha, am->sha, sizeof(resp.am.tha)); memcpy(resp.am.tip, am->sip, sizeof(resp.am.tip)); diff --git a/fwd.c b/fwd.c index ab49dba..664e167 100644 --- a/fwd.c +++ b/fwd.c @@ -630,8 +630,8 @@ static bool fwd_guest_accessible(const struct ctx *c, * Only handles translations that depend *only* on the address. Anything * related to specific ports or flows is handled elsewhere. */ -static void nat_outbound(const struct ctx *c, const union inany_addr *addr, - union inany_addr *translated) +void nat_outbound(const struct ctx *c, const union inany_addr *addr, + union inany_addr *translated)
Since this is now exported, it should become fwd_nat_outbound() to namespace it properly.
{ if (inany_equals4(addr, &c->ip4.map_host_loopback)) *translated = inany_loopback4; @@ -643,6 +643,7 @@ static void nat_outbound(const struct ctx *c, const union inany_addr *addr, translated->a6 = c->ip6.addr; else *translated = *addr; +
Spurious whitespace.
}
/** diff --git a/fwd.h b/fwd.h index 80da4b1..bf1705b 100644 --- a/fwd.h +++ b/fwd.h @@ -57,6 +57,8 @@ void fwd_scan_ports_init(struct ctx *c);
bool nat_inbound(const struct ctx *c, const union inany_addr *addr, union inany_addr *translated); +void nat_outbound(const struct ctx *c, const union inany_addr *addr, + union inany_addr *translated); uint8_t fwd_nat_from_tap(const struct ctx *c, uint8_t proto, const struct flowside *ini, struct flowside *tgt); uint8_t fwd_nat_from_splice(const struct ctx *c, uint8_t proto, diff --git a/inany.c b/inany.c index 65a39f9..7680439 100644 --- a/inany.c +++ b/inany.c @@ -16,6 +16,7 @@ #include "ip.h" #include "siphash.h" #include "inany.h" +#include "fwd.h"
const union inany_addr inany_loopback4 = INANY_INIT4(IN4ADDR_LOOPBACK_INIT); const union inany_addr inany_any4 = INANY_INIT4(IN4ADDR_ANY_INIT); diff --git a/ndp.c b/ndp.c index eb090cd..820c556 100644 --- a/ndp.c +++ b/ndp.c @@ -196,6 +196,7 @@ static void ndp_send(const struct ctx *c, const struct in6_addr *dst, static void ndp_na(const struct ctx *c, const struct in6_addr *dst, const struct in6_addr *addr) { + union inany_addr tgt, tgt_nat; struct ndp_na na = { .ih = { .icmp6_type = NA, @@ -215,6 +216,13 @@ static void ndp_na(const struct ctx *c, const struct in6_addr *dst,
memcpy(na.target_l2_addr.mac, c->our_tap_mac, ETH_ALEN);
+ /* Respond with true MAC address if remote host's address or + * NAT translated address can be found in NDP table. + */ + inany_from_af(&tgt, AF_INET6, addr); + nat_outbound(c, &tgt, &tgt_nat); + fwd_neigh_mac_get(c, &tgt_nat, na.target_l2_addr.mac); + ndp_send(c, dst, &na, sizeof(na)); }
-- 2.50.1
-- David Gibson (he or they) | I'll have my music baroque, and my code david AT gibson.dropbear.id.au | minimalist, thank you, not the other way | around. http://www.ozlabs.org/~dgibson