linux-kernel - Re: [PATCH net] net: fix segmentation after TCP/UDP fraglist GRO

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Message-ID: <2c84bde8-5d5a-467f-a7ac-791207e7903a@nbd.name>
Date: Fri, 11 Jul 2025 14:06:57 +0200
From: Felix Fietkau <nbd@....name>
To: Willem de Bruijn <willemdebruijn.kernel@...il.com>,
 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: Re: [PATCH net] net: fix segmentation after TCP/UDP fraglist GRO

On 06.07.25 15:45, Willem de Bruijn wrote:
> Felix Fietkau wrote:
>> 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()
> 
> Only ip_hdr is in scope.
> 
> Reviewing TCP and UDP GSO, tcp_hdr/transport header is used also
> outside segment list. Non segment list GSO also uses ip_hdr in case
> pseudo checksum needs to be set.
Will change that in v2, thanks.
> The GSO code is called with skb->data at the relevant header, so L4
> helpers are not strictly needed. The main issue is that data will be
> at the L4 header, and some GSO code also needs to see the IP header
> (e.g., for aforementioned pseudo checksum calculation).
> 
>> to check for address/port changes.
> 
> If in GSO, then the headers are probably more correctly set at the end
> of GRO, in gro_complete.

Just to clarify, in inet/ipv6_gro_complete you want me to iterate over 
all fragment skbs, calculate the header offset based on the first skb, 
and set it?

- Felix