[PATCH 6.18 090/122] net: fix segmentation of forwarding fraglist GRO

Greg Kroah-Hartman
2026-02-04T15:33:01Z

From: Jibin Zhang <jibin.zhang@mediatek.com>

commit 426ca15c7f6cb6562a081341ca88893a50c59fa2 upstream.

This patch enhances GSO segment handling by properly checking
the SKB_GSO_DODGY flag for frag_list GSO packets, addressing
low throughput issues observed when a station accesses IPv4
servers via hotspots with an IPv6-only upstream interface.

Specifically, it fixes a bug in GSO segmentation when forwarding
GRO packets containing a frag_list. The function skb_segment_list
cannot correctly process GRO skbs that have been converted by XLAT,
since XLAT only translates the header of the head skb. Consequently,
skbs in the frag_list may remain untranslated, resulting in protocol
inconsistencies and reduced throughput.

To address this, the patch explicitly sets the SKB_GSO_DODGY flag
for GSO packets in XLAT's IPv4/IPv6 protocol translation helpers
(bpf_skb_proto_4_to_6 and bpf_skb_proto_6_to_4). This marks GSO
packets as potentially modified after protocol translation. As a
result, GSO segmentation will avoid using skb_segment_list and
instead falls back to skb_segment for packets with the SKB_GSO_DODGY
flag. This ensures that only safe and fully translated frag_list
packets are processed by skb_segment_list, resolving protocol
inconsistencies and improving throughput when forwarding GRO packets
converted by XLAT.

Signed-off-by: Jibin Zhang <jibin.zhang@mediatek.com>
Fixes: 9fd1ff5d2ac7 ("udp: Support UDP fraglist GRO/GSO.")
Cc: stable@vger.kernel.org
Link: https://patch.msgid.link/20260126152114.1211-1-jibin.zhang@mediatek.com
Signed-off-by: Paolo Abeni <pabeni@redhat.com>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>
---
net/core/filter.c | 2 ++
net/ipv4/tcp_offload.c | 3 ++-
net/ipv4/udp_offload.c | 3 ++-
net/ipv6/tcpv6_offload.c | 3 ++-
4 files changed, 8 insertions(+), 3 deletions(-)

--- a/net/core/filter.c
+++ b/net/core/filter.c
@@ -3352,6 +3352,7 @@ static int bpf_skb_proto_4_to_6(struct s
shinfo->gso_type &= ~SKB_GSO_TCPV4;
shinfo->gso_type |= SKB_GSO_TCPV6;
}
+ shinfo->gso_type |= SKB_GSO_DODGY;
}

bpf_skb_change_protocol(skb, ETH_P_IPV6);
@@ -3382,6 +3383,7 @@ static int bpf_skb_proto_6_to_4(struct s
shinfo->gso_type &= ~SKB_GSO_TCPV6;
shinfo->gso_type |= SKB_GSO_TCPV4;
}
+ shinfo->gso_type |= SKB_GSO_DODGY;
}

bpf_skb_change_protocol(skb, ETH_P_IP);
--- a/net/ipv4/tcp_offload.c
+++ b/net/ipv4/tcp_offload.c
@@ -107,7 +107,8 @@ static struct sk_buff *tcp4_gso_segment(
if (skb_shinfo(skb)->gso_type & SKB_GSO_FRAGLIST) {
struct tcphdr *th = tcp_hdr(skb);

- if (skb_pagelen(skb) - th->doff * 4 == skb_shinfo(skb)->gso_size)
+ if ((skb_pagelen(skb) - th->doff * 4 == skb_shinfo(skb)->gso_size) &&
+ !(skb_shinfo(skb)->gso_type & SKB_GSO_DODGY))
return __tcp4_gso_segment_list(skb, features);

skb->ip_summed = CHECKSUM_NONE;
--- a/net/ipv4/udp_offload.c
+++ b/net/ipv4/udp_offload.c
@@ -514,7 +514,8 @@ struct sk_buff *__udp_gso_segment(struct

if (skb_shinfo(gso_skb)->gso_type & SKB_GSO_FRAGLIST) {
/* Detect modified geometry and pass those to skb_segment. */
- if (skb_pagelen(gso_skb) - sizeof(*uh) == skb_shinfo(gso_skb)->gso_size)
+ if ((skb_pagelen(gso_skb) - sizeof(*uh) == skb_shinfo(gso_skb)->gso_size) &&
+ !(skb_shinfo(gso_skb)->gso_type & SKB_GSO_DODGY))
return __udp_gso_segment_list(gso_skb, features, is_ipv6);

ret = __skb_linearize(gso_skb);
--- a/net/ipv6/tcpv6_offload.c
+++ b/net/ipv6/tcpv6_offload.c
@@ -170,7 +170,8 @@ static struct sk_buff *tcp6_gso_segment(
if (skb_shinfo(skb)->gso_type & SKB_GSO_FRAGLIST) {
struct tcphdr *th = tcp_hdr(skb);

- if (skb_pagelen(skb) - th->doff * 4 == skb_shinfo(skb)->gso_size)
+ if ((skb_pagelen(skb) - th->doff * 4 == skb_shinfo(skb)->gso_size) &&
+ !(skb_shinfo(skb)->gso_type & SKB_GSO_DODGY))
return __tcp6_gso_segment_list(skb, features);

skb->ip_summed = CHECKSUM_NONE;