netdev - [PATCH v2] net: fix segmentation of forwarding fraglist GRO

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Message-ID: <20260111112355.21504-1-jibin.zhang@mediatek.com>
Date: Sun, 11 Jan 2026 19:23:46 +0800
From: Jibin Zhang <jibin.zhang@...iatek.com>
To: Eric Dumazet <edumazet@...gle.com>, Neal Cardwell <ncardwell@...gle.com>,
	Kuniyuki Iwashima <kuniyu@...gle.com>, "David S . Miller"
	<davem@...emloft.net>, David Ahern <dsahern@...nel.org>, Jakub Kicinski
	<kuba@...nel.org>, Paolo Abeni <pabeni@...hat.com>, Simon Horman
	<horms@...nel.org>, Matthias Brugger <matthias.bgg@...il.com>,
	AngeloGioacchino Del Regno <angelogioacchino.delregno@...labora.com>,
	<netdev@...r.kernel.org>, <linux-kernel@...r.kernel.org>,
	<linux-arm-kernel@...ts.infradead.org>, <linux-mediatek@...ts.infradead.org>
CC: <wsd_upstream@...iatek.com>, <jibin.zhang@...iatek.com>
Subject: [PATCH v2] net: fix segmentation of forwarding fraglist GRO

This patch enhances GSO segment checks by verifying the presence
of frag_list and protocol consistency, addressing low throughput
issues on IPv4 servers when used as hotspots

Specifically, it fixes a bug in GSO segmentation when forwarding
GRO packets with frag_list. The function skb_segment_list cannot
correctly process GRO skbs converted by XLAT, because XLAT only
converts the header of the head skb. As a result, skbs in the
frag_list may remain unconverted, leading to protocol
inconsistencies and reduced throughput.

To resolve this, the patch uses skb_segment to handle forwarded
packets converted by XLAT, ensuring that all fragments are
properly converted and segmented.

Signed-off-by: Jibin Zhang <jibin.zhang@...iatek.com>
---
v2: To apply the added condition to a narrower scop

  In this version, the condition (skb_has_frag_list(gso_skb) &&
(gso_skb->protocol == skb_shinfo(gso_skb)->frag_list->protocol))
is moved into inner 'if' statement to a narrower scope.

  Send out the patch again for further discussion because:

1. This issue has a significant impact and has occurred in many
countries and regions.
2. Currently, modifying BPF is not a good option, because BPF code
cannot access the header of skb on the fraglist, and the required
changes would affect a wide range of code.
3. Directly disabling GRO aggregation for XLAT flows is also not a
good solution, as this change would disable GRO even when forwarding
is not needed, and it would also require cooperation from all device
drivers.

[1]: https//patchwork.kernel.org/patch/14350844

---
 net/ipv4/tcp_offload.c | 4 +++-
 net/ipv4/udp_offload.c | 4 +++-
 2 files changed, 6 insertions(+), 2 deletions(-)

diff --git a/net/ipv4/tcp_offload.c b/net/ipv4/tcp_offload.c
index fdda18b1abda..6c2c10f37f87 100644
--- a/net/ipv4/tcp_offload.c
+++ b/net/ipv4/tcp_offload.c
@@ -107,7 +107,9 @@ static struct sk_buff *tcp4_gso_segment(struct sk_buff *skb,
 	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_has_frag_list(skb) &&
+		    (skb->protocol == skb_shinfo(skb)->frag_list->protocol))
 			return __tcp4_gso_segment_list(skb, features);
 
 		skb->ip_summed = CHECKSUM_NONE;
diff --git a/net/ipv4/udp_offload.c b/net/ipv4/udp_offload.c
index 19d0b5b09ffa..2a99f011793f 100644
--- a/net/ipv4/udp_offload.c
+++ b/net/ipv4/udp_offload.c
@@ -514,7 +514,9 @@ struct sk_buff *__udp_gso_segment(struct sk_buff *gso_skb,
 
 	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_has_frag_list(gso_skb) &&
+		    (gso_skb->protocol == skb_shinfo(gso_skb)->frag_list->protocol))
 			return __udp_gso_segment_list(gso_skb, features, is_ipv6);
 
 		ret = __skb_linearize(gso_skb);
-- 
2.45.2