netdev - Re: [PATCH net 1/2] net: gro: fix outer network offset

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Message-ID: <willemdebruijn.kernel.38507b06f982e@gmail.com>
Date: Sun, 01 Feb 2026 17:21:51 -0500
From: Willem de Bruijn <willemdebruijn.kernel@...il.com>
To: Paolo Abeni <pabeni@...hat.com>, 
 netdev@...r.kernel.org
Cc: "David S. Miller" <davem@...emloft.net>, 
 Eric Dumazet <edumazet@...gle.com>, 
 Jakub Kicinski <kuba@...nel.org>, 
 Simon Horman <horms@...nel.org>, 
 Shuah Khan <shuah@...nel.org>, 
 Willem de Bruijn <willemb@...gle.com>, 
 Richard Gobert <richardbgobert@...il.com>, 
 linux-kselftest@...r.kernel.org
Subject: Re: [PATCH net 1/2] net: gro: fix outer network offset

Paolo Abeni wrote:
> The udp GRO complete stage assumes that all the packets inserted the RX
> have the `encapsulation` flag zeroed. Such assumption is not true, as a
> few H/W NICs can set such flag when H/W offloading the checksum for
> an UDP encapsulated traffic, the tun driver can inject GSO packets with
> UDP encapsulation and the problematic layout can also be created via
> a veth based setup.
> 
> Due to the above, in the problematic scenarios, udp4_gro_complete() uses
> the wrong network offset (inner instead of outer) to compute the outer
> UDP header pseudo checksum, leading to csum validation errors later on
> in packet processing.
> 
> Address the issue always clearing the encapsulation flag at GRO completion
> time. Such flag will be set again as needed for encapsulated packets by
> udp_gro_complete().
> 
> Fixes: 5ef31ea5d053 ("net: gro: fix udp bad offset in socket lookup by adding {inner_}network_offset to napi_gro_cb")
> Signed-off-by: Paolo Abeni <pabeni@...hat.com>

Reviewed-by: Willem de Bruijn <willemb@...gle.com>