[PATCH 6.6.y 3/3] net: fix segmentation of forwarding fraglist GRO

[Li hongliang]

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

[ Upstream commit 426ca15c7f6cb6562a081341ca88893a50c59fa2 ]

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 at mediatek.com>
Fixes: 9fd1ff5d2ac7 ("udp: Support UDP fraglist GRO/GSO.")
Cc: stable at vger.kernel.org
Link: https://patch.msgid.link/20260126152114.1211-1-jibin.zhang@mediatek.com
Signed-off-by: Paolo Abeni <pabeni at redhat.com>
Signed-off-by: Li hongliang <1468888505 at 139.com>
---
 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(-)

diff --git a/net/core/filter.c b/net/core/filter.c
index ddb6d3dd34de..1732358b96ad 100644
--- a/net/core/filter.c
+++ b/net/core/filter.c
@@ -3340,6 +3340,7 @@ static int bpf_skb_proto_4_to_6(struct sk_buff *skb)
 			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);
@@ -3370,6 +3371,7 @@ static int bpf_skb_proto_6_to_4(struct sk_buff *skb)
 			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);
diff --git a/net/ipv4/tcp_offload.c b/net/ipv4/tcp_offload.c
index 36595709279c..7b09f6d0818b 100644
--- a/net/ipv4/tcp_offload.c
+++ b/net/ipv4/tcp_offload.c
@@ -107,7 +107,8 @@ 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_shinfo(skb)->gso_type & SKB_GSO_DODGY))
 			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 9be9df2caf65..cd860d8d497b 100644
--- a/net/ipv4/udp_offload.c
+++ b/net/ipv4/udp_offload.c
@@ -352,7 +352,8 @@ 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_shinfo(gso_skb)->gso_type & SKB_GSO_DODGY))
 			return __udp_gso_segment_list(gso_skb, features, is_ipv6);
 
 		ret = __skb_linearize(gso_skb);
diff --git a/net/ipv6/tcpv6_offload.c b/net/ipv6/tcpv6_offload.c
index 7567c32670c6..10025c9e07d3 100644
--- a/net/ipv6/tcpv6_offload.c
+++ b/net/ipv6/tcpv6_offload.c
@@ -109,7 +109,8 @@ static struct sk_buff *tcp6_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_shinfo(skb)->gso_type & SKB_GSO_DODGY))
 			return __tcp6_gso_segment_list(skb, features);
 
 		skb->ip_summed = CHECKSUM_NONE;
-- 
2.34.1