linux-kernel - Re: [PATCH net-next v4 4/4] net: gro: move L3 flush checks to tcp_gro

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Message-ID: <46e0c775-91e7-4bf6-88f3-53ab5e00414f@gmail.com>
Date: Tue, 26 Mar 2024 15:43:42 +0100
From: Richard Gobert <richardbgobert@...il.com>
To: Eric Dumazet <edumazet@...gle.com>
Cc: davem@...emloft.net, kuba@...nel.org, pabeni@...hat.com,
 willemdebruijn.kernel@...il.com, netdev@...r.kernel.org,
 linux-kernel@...r.kernel.org, linux-kselftest@...r.kernel.org
Subject: Re: [PATCH net-next v4 4/4] net: gro: move L3 flush checks to
 tcp_gro_receive

Eric Dumazet wrote:
> On Mon, Mar 25, 2024 at 7:27 PM Richard Gobert <richardbgobert@...il.com> wrote:
>>
>> {inet,ipv6}_gro_receive functions perform flush checks (ttl, flags,
>> iph->id, ...) against all packets in a loop. These flush checks are used
>> currently only in tcp flows in GRO.
> 
> I think this is a bug.
> 
> GRO should not aggregate packets if their ttl/tos fields do not match.

AFAIU, the only UDP flow where ttl/flush_id need to be checked is when
udp_gro_receive_segment calls skb_gro_receive - could you confirm / point
out if there are any other flows to which these flush checks may be
relevant?

As I've discussed with Willem in v3 I prefer to fix this bug in a separate
series.