netdev - [PATCH net] net: fix segmentation after TCP/UDP fraglist GRO

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Message-ID: <20250705150622.10699-1-nbd@nbd.name>
Date: Sat,  5 Jul 2025 17:06:21 +0200
From: Felix Fietkau <nbd@....name>
To: netdev@...r.kernel.org,
	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>,
	Willem de Bruijn <willemb@...gle.com>,
	Richard Gobert <richardbgobert@...il.com>
Cc: linux-kernel@...r.kernel.org
Subject: [PATCH net] net: fix segmentation after TCP/UDP fraglist GRO

Since "net: gro: use cb instead of skb->network_header", the skb network
header is no longer set in the GRO path.
This breaks fraglist segmentation, which relies on ip_hdr()/tcp_hdr()
to check for address/port changes.
Fix this regression by selectively setting the network header for merged
segment skbs.

Fixes: 186b1ea73ad8 ("net: gro: use cb instead of skb->network_header")
Signed-off-by: Felix Fietkau <nbd@....name>
---
 net/ipv4/tcp_offload.c | 1 +
 net/ipv4/udp_offload.c | 1 +
 2 files changed, 2 insertions(+)

diff --git a/net/ipv4/tcp_offload.c b/net/ipv4/tcp_offload.c
index d293087b426d..be5c2294610e 100644
--- a/net/ipv4/tcp_offload.c
+++ b/net/ipv4/tcp_offload.c
@@ -359,6 +359,7 @@ struct sk_buff *tcp_gro_receive(struct list_head *head, struct sk_buff *skb,
 		flush |= skb->ip_summed != p->ip_summed;
 		flush |= skb->csum_level != p->csum_level;
 		flush |= NAPI_GRO_CB(p)->count >= 64;
+		skb_set_network_header(skb, skb_gro_receive_network_offset(skb));
 
 		if (flush || skb_gro_receive_list(p, skb))
 			mss = 1;
diff --git a/net/ipv4/udp_offload.c b/net/ipv4/udp_offload.c
index 85b5aa82d7d7..e0a6bfa95118 100644
--- a/net/ipv4/udp_offload.c
+++ b/net/ipv4/udp_offload.c
@@ -767,6 +767,7 @@ static struct sk_buff *udp_gro_receive_segment(struct list_head *head,
 					NAPI_GRO_CB(skb)->flush = 1;
 					return NULL;
 				}
+				skb_set_network_header(skb, skb_gro_receive_network_offset(skb));
 				ret = skb_gro_receive_list(p, skb);
 			} else {
 				skb_gro_postpull_rcsum(skb, uh,
-- 
2.49.0