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tap_user: fix DHCP lease renewal losing guest connectivity #325

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Merged
LekKit merged 1 commit into from
Oct 5, 2026
Merged

tap_user: fix DHCP lease renewal losing guest connectivity #325

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16 changes: 9 additions & 7 deletions src/devices/tap_user.c
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Original file line number Diff line number Diff line change
Expand Up @@ -352,7 +352,8 @@ static void handle_dhcp(tap_dev_t* tap, const uint8_t* buffer, size_t size, net_

uint8_t frame[TAP_FRAME_SIZE];
uint8_t* ipv4 = create_eth_frame(tap, frame, ETH2_IPv4);
uint8_t* udp = create_ipv4_frame(ipv4, 278 + UDP_HDR_SIZE, IP_PROTO_UDP, (const uint8_t*)"\xFF\xFF\xFF\xFF", GATEWAY_IP);
const uint8_t* reply_ip = read_uint32_be_m(buffer + 12) ? buffer + 12 : (const uint8_t*)"\xFF\xFF\xFF\xFF";
uint8_t* udp = create_ipv4_frame(ipv4, 278 + UDP_HDR_SIZE, IP_PROTO_UDP, reply_ip, GATEWAY_IP);
uint8_t* dhcp = create_udp_datagram(udp, 278, 68, 67);

dhcp[0] = OP_RESPONSE;
Expand Down Expand Up @@ -450,15 +451,16 @@ static void handle_udp(tap_dev_t* tap, const uint8_t* buffer, size_t size, net_a
}
udp_size -= UDP_HDR_SIZE;

// Renewals use the leased source IP; intercept before any UDP forwarding entry.
if (src->type == NET_TYPE_IPV4 && src->port == 68 && dst->port == 67
&& (memcmp(dst->ip, GATEWAY_IP, PLEN_IPv4) == 0 || read_uint32_be_m(dst->ip) == 0xFFFFFFFF)) {
handle_dhcp(tap, udb_buff, udp_size, src);
return;
}

spin_lock(&tap->lock);
tap_sock_t* ts = (tap_sock_t*)hashmap_get(&tap->udp_ports, src->port);
if (ts == NULL) {
if (dst->port == 67 && (read_uint32_be_m(src->ip) == 0)) {
spin_unlock(&tap->lock);
handle_dhcp(tap, udb_buff, udp_size, src);
return;
}

net_sock_t* sock = net_udp_bind(NET_IPV4_ANY);
net_sock_set_blocking(sock, false);
if (sock) {
Expand Down
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