On Fri, Sep 05, 2025 at 10:11:50PM -0400, Jon Maloy wrote:
We forward the incoming MAC address through the tap interface when receiving incoming packets from network local hosts.
This is a part of the solution to bug https://bugs.passt.top/show_bug.cgi?id=120
Signed-off-by: Jon Maloy
Reviewed-by: David Gibson
--- v3: - Adapted to the move of external MAC address from struct flowside to struct flow_common v4: - Changed signature of udp_tap_prepare() to take a MAC address instead of a flow. - Eliminated initialization of MAC source address in all frames, since those now are set per send occasion anyway. v5: - Added lookup in ARP/NDP table on incoming messages in case flow->tap_omac wasn't initialized at flow creation, i.e., the flow was initiated from the guest. --- passt.c | 2 +- udp.c | 45 +++++++++++++++++++++++++-------------------- udp.h | 2 +- 3 files changed, 27 insertions(+), 22 deletions(-)
diff --git a/passt.c b/passt.c index a4ec115..2a28e20 100644 --- a/passt.c +++ b/passt.c @@ -154,7 +154,7 @@ static void timer_init(struct ctx *c, const struct timespec *now) void proto_update_l2_buf(const unsigned char *eth_d, const unsigned char *eth_s) { tcp_update_l2_buf(eth_d, eth_s); - udp_update_l2_buf(eth_d, eth_s); + udp_update_l2_buf(eth_d); }
/** diff --git a/udp.c b/udp.c index 86585b7..7d98845 100644 --- a/udp.c +++ b/udp.c @@ -133,11 +133,8 @@ static int udp_splice_init[IP_VERSIONS][NUM_PORTS]; /* UDP header and data for inbound messages */ static struct udp_payload_t udp_payload[UDP_MAX_FRAMES];
-/* Ethernet header for IPv4 frames */ -static struct ethhdr udp4_eth_hdr; - -/* Ethernet header for IPv6 frames */ -static struct ethhdr udp6_eth_hdr; +/* Ethernet headers for IPv4 and IPv6 frames */ +static struct ethhdr udp_eth_hdr[UDP_MAX_FRAMES];
/** * struct udp_meta_t - Pre-cooked headers for UDP packets @@ -210,12 +207,13 @@ void udp_portmap_clear(void) /** * udp_update_l2_buf() - Update L2 buffers with Ethernet and IPv4 addresses * @eth_d: Ethernet destination address, NULL if unchanged - * @eth_s: Ethernet source address, NULL if unchanged */ -void udp_update_l2_buf(const unsigned char *eth_d, const unsigned char *eth_s) +void udp_update_l2_buf(const unsigned char *eth_d) { - eth_update_mac(&udp4_eth_hdr, eth_d, eth_s); - eth_update_mac(&udp6_eth_hdr, eth_d, eth_s); + int i; + + for (i = 0; i < UDP_MAX_FRAMES; i++) + eth_update_mac(&udp_eth_hdr[i], eth_d, NULL); }
/** @@ -238,6 +236,7 @@ static void udp_iov_init_one(const struct ctx *c, size_t i)
*siov = IOV_OF_LVALUE(payload->data);
+ tiov[UDP_IOV_ETH] = IOV_OF_LVALUE(udp_eth_hdr[i]); tiov[UDP_IOV_TAP] = tap_hdr_iov(c, &meta->taph); tiov[UDP_IOV_PAYLOAD].iov_base = payload;
@@ -253,9 +252,6 @@ static void udp_iov_init(const struct ctx *c) { size_t i;
- udp4_eth_hdr.h_proto = htons_constant(ETH_P_IP); - udp6_eth_hdr.h_proto = htons_constant(ETH_P_IPV6); - for (i = 0; i < UDP_MAX_FRAMES; i++) udp_iov_init_one(c, i); } @@ -352,31 +348,34 @@ size_t udp_update_hdr6(struct ipv6hdr *ip6h, struct udp_payload_t *bp, * udp_tap_prepare() - Convert one datagram into a tap frame * @mmh: Receiving mmsghdr array * @idx: Index of the datagram to prepare + * @tap_omac: MAC address of remote endpoint as seen from the guest * @toside: Flowside for destination side * @no_udp_csum: Do not set UDP checksum */ static void udp_tap_prepare(const struct mmsghdr *mmh, - unsigned idx, const struct flowside *toside, + unsigned int idx, + const uint8_t *tap_omac, + const struct flowside *toside, bool no_udp_csum) { struct iovec (*tap_iov)[UDP_NUM_IOVS] = &udp_l2_iov[idx]; struct udp_payload_t *bp = &udp_payload[idx]; struct udp_meta_t *bm = &udp_meta[idx]; + struct ethhdr *eh = (*tap_iov)[UDP_IOV_ETH].iov_base; size_t l4len;
+ eth_update_mac(eh, NULL, tap_omac); if (!inany_v4(&toside->eaddr) || !inany_v4(&toside->oaddr)) { l4len = udp_update_hdr6(&bm->ip6h, bp, toside, mmh[idx].msg_len, no_udp_csum); - tap_hdr_update(&bm->taph, l4len + sizeof(bm->ip6h) + - sizeof(udp6_eth_hdr)); - (*tap_iov)[UDP_IOV_ETH] = IOV_OF_LVALUE(udp6_eth_hdr); + tap_hdr_update(&bm->taph, l4len + sizeof(bm->ip6h) + ETH_HLEN); + eh->h_proto = htons_constant(ETH_P_IPV6); (*tap_iov)[UDP_IOV_IP] = IOV_OF_LVALUE(bm->ip6h); } else { l4len = udp_update_hdr4(&bm->ip4h, bp, toside, mmh[idx].msg_len, no_udp_csum); - tap_hdr_update(&bm->taph, l4len + sizeof(bm->ip4h) + - sizeof(udp4_eth_hdr)); - (*tap_iov)[UDP_IOV_ETH] = IOV_OF_LVALUE(udp4_eth_hdr); + tap_hdr_update(&bm->taph, l4len + sizeof(bm->ip4h) + ETH_HLEN); + eh->h_proto = htons_constant(ETH_P_IP); (*tap_iov)[UDP_IOV_IP] = IOV_OF_LVALUE(bm->ip4h); } (*tap_iov)[UDP_IOV_PAYLOAD].iov_len = l4len; @@ -801,13 +800,19 @@ static void udp_buf_sock_to_tap(const struct ctx *c, int s, int n, flow_sidx_t tosidx) { const struct flowside *toside = flowside_at_sidx(tosidx); + struct udp_flow *uflow = udp_at_sidx(tosidx); + uint8_t *omac = uflow->f.tap_omac; int i;
if ((n = udp_sock_recv(c, s, udp_mh_recv, n)) <= 0) return;
+ /* Make one attempt to find true MAC address in ARP/NDP table */ + if (mac_undefined(omac)) + fwd_neigh_mac_get(c, &toside->oaddr, omac); + for (i = 0; i < n; i++) - udp_tap_prepare(udp_mh_recv, i, toside, false); + udp_tap_prepare(udp_mh_recv, i, omac, toside, false);
tap_send_frames(c, &udp_l2_iov[0][0], UDP_NUM_IOVS, n); } diff --git a/udp.h b/udp.h index 8f8531a..dd6e5ad 100644 --- a/udp.h +++ b/udp.h @@ -21,7 +21,7 @@ int udp_sock_init(const struct ctx *c, int ns, const union inany_addr *addr, const char *ifname, in_port_t port); int udp_init(struct ctx *c); void udp_timer(struct ctx *c, const struct timespec *now); -void udp_update_l2_buf(const unsigned char *eth_d, const unsigned char *eth_s); +void udp_update_l2_buf(const unsigned char *eth_d);
/** * union udp_listen_epoll_ref - epoll reference for "listening" UDP sockets -- 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