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Date: Tue, 26 Mar 2024 15:43:42 +0100
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Subject: Re: [PATCH net-next v4 4/4] net: gro: move L3 flush checks to
 tcp_gro_receive
To: Eric Dumazet <edumazet@google.com>
Cc: davem@davemloft.net, kuba@kernel.org, pabeni@redhat.com,
 willemdebruijn.kernel@gmail.com, netdev@vger.kernel.org,
 linux-kernel@vger.kernel.org, linux-kselftest@vger.kernel.org
References: <20240325182543.87683-1-richardbgobert@gmail.com>
 <20240325182543.87683-5-richardbgobert@gmail.com>
 <CANn89iKzeTKuBA3NL0DQUmUHmmc0QzZ0X62DUarZ2Q7cKRZvSA@mail.gmail.com>
From: Richard Gobert <richardbgobert@gmail.com>
In-Reply-To: <CANn89iKzeTKuBA3NL0DQUmUHmmc0QzZ0X62DUarZ2Q7cKRZvSA@mail.gmail.com>
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Eric Dumazet wrote:
> On Mon, Mar 25, 2024 at 7:27 PM Richard Gobert <richardbgobert@gmail.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.