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[client] Clear stale UDP checksum in eBPF XDP proxy after port rewrite (#6861)

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This commit is contained in:
Viktor Liu
2026-07-23 21:37:52 +09:00
committed by GitHub
parent 0936918d24
commit 6d15d0729a
4 changed files with 9 additions and 0 deletions
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client/internal/ebpf/ebpf/bpf_bpfeb.o
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client/internal/ebpf/ebpf/bpf_bpfel.o
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3
client/internal/ebpf/ebpf/src/dns_fwd.c
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@@ -52,11 +52,14 @@ int xdp_dns_fwd(struct iphdr *ip, struct udphdr *udp) {
if (udp->dest == GENERAL_DNS_PORT && ip->daddr == dns_ip) {
udp->dest = dns_port;
// Clear the now-stale checksum; zero means "not computed" for IPv4.
udp->check = 0;
return XDP_PASS;
}
if (udp->source == dns_port && ip->saddr == dns_ip) {
udp->source = GENERAL_DNS_PORT;
udp->check = 0;
return XDP_PASS;
}

6
client/internal/ebpf/ebpf/src/wg_proxy.c
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@@ -50,5 +50,11 @@ int xdp_wg_proxy(struct iphdr *ip, struct udphdr *udp) {
__be16 new_dst_port = htons(proxy_port);
udp->dest = new_dst_port;
udp->source = new_src_port;
// The ports are covered by the UDP checksum. This is an IPv4 loopback hop
// and the payload is already integrity-protected, so clear the checksum (a
// zero UDP checksum means "not computed" for IPv4) rather than leave a
// stale value the kernel would drop as UDP_CSUM.
udp->check = 0;
return XDP_PASS;
}