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bpf: Update transport_header when encapsulating UDP tunnel in lwt

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Currently, bpf_lwt_push_ip_encap() does not update skb->transport_header.
When a driver, e.g. ice, reuses the stale skb->transport_header to
offload checksum computation to NIC hardware, VxLAN packets encapsulated
by bpf_lwt_push_encap() helper may be dropped due to incorrect checksum.

Update skb->transport_header in bpf_lwt_push_ip_encap() whenever the
encapsulated packet uses UDP, so checksum offload works correctly.

Fixes: 52f278774e ("bpf: implement BPF_LWT_ENCAP_IP mode in bpf_lwt_push_encap")
Cc: Leon Hwang <leon.huangfu@shopee.com>
Signed-off-by: Leon Hwang <leon.hwang@linux.dev>
Link: https://lore.kernel.org/r/20260602150931.49629-2-leon.hwang@linux.dev
Signed-off-by: Alexei Starovoitov <ast@kernel.org>
This commit is contained in:
Leon Hwang 2026-06-02 23:09:30 +08:00 committed by Alexei Starovoitov
parent b984529052
commit 82d7d0adbc
1 changed files with 12 additions and 0 deletions
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12
net/core/lwt_bpf.c
View File

@ -599,6 +599,7 @@ static int handle_gso_encap(struct sk_buff *skb, bool ipv4, int encap_len)
int bpf_lwt_push_ip_encap(struct sk_buff *skb, void *hdr, u32 len, bool ingress)
{
bool is_udp_tunnel;
struct iphdr *iph;
bool ipv4;
int err;
@ -612,10 +613,16 @@ int bpf_lwt_push_ip_encap(struct sk_buff *skb, void *hdr, u32 len, bool ingress)
ipv4 = true;
if (unlikely(len < iph->ihl * 4))
return -EINVAL;
is_udp_tunnel = iph->protocol == IPPROTO_UDP;
if (unlikely(is_udp_tunnel && len < iph->ihl * 4 + sizeof(struct udphdr)))
return -EINVAL;
} else if (iph->version == 6) {
ipv4 = false;
if (unlikely(len < sizeof(struct ipv6hdr)))
return -EINVAL;
is_udp_tunnel = ((struct ipv6hdr *)iph)->nexthdr == NEXTHDR_UDP;
if (unlikely(is_udp_tunnel && len < sizeof(struct ipv6hdr) + sizeof(struct udphdr)))
return -EINVAL;
} else {
return -EINVAL;
}
@ -637,6 +644,11 @@ int bpf_lwt_push_ip_encap(struct sk_buff *skb, void *hdr, u32 len, bool ingress)
if (ingress)
skb_postpush_rcsum(skb, iph, len);
skb_reset_network_header(skb);
if (is_udp_tunnel) {
size_t iph_sz = ipv4 ? iph->ihl * 4 : sizeof(struct ipv6hdr);
skb_set_transport_header(skb, skb_network_offset(skb) + iph_sz);
}
memcpy(skb_network_header(skb), hdr, len);
bpf_compute_data_pointers(skb);
skb_clear_hash(skb);