Re: [PATCH net v4 1/2] ip6_gre: fix hardware header length for NBMA tunnels

[Paolo Abeni <pabeni@redhat.com>]

On 8/17/26 8:42 AM, Ido Schimmel wrote:
> On Thu, Aug 13, 2026 at 12:22:34AM +0800, Zhiling Zou wrote:
>> ip6gre_tnl_link_config_route() accumulates the lower device's hardware
>> header length into dev->hard_header_len whenever header_ops is set. This
>> is incorrect for both users of header_ops.
>>
>> ip6gretap and ip6erspan have a fixed Ethernet hardware header length.
>> For an NBMA ip6gre tunnel, ip6gre_header() creates only the GRE header,
>> the optional FOU or GUE header, and the outer IPv6 header. The lower
>> device header is headroom needed later, not part of the tunnel device's
>> hardware header.
>>
>> Keep the lower device header in needed_headroom. Set hard_header_len to
>> the tunnel header length only for ARPHRD_IP6GRE devices with header_ops,
>> and leave the fixed Ethernet header length unchanged for tap and erspan
>> devices.
>>
>> Fixes: 832ba596494b ("net: ip6_gre: set dev->hard_header_len when using header_ops")
>> Cc: stable@vger.kernel.org
>> Reported-by: Vega <vega@nebusec.ai>
> 
> It wasn't reported by Vega.
> 
>> Suggested-by: Ido Schimmel <idosch@nvidia.com>
>> Signed-off-by: Zhiling Zou <zhilinz@nebusec.ai>
> 
> Reviewed-by: Ido Schimmel <idosch@nvidia.com>
Thanks for all the reviewing effort!

FYI, since some time, the nipa sashiko instance is using as input
gemini-sashiko reviews, and cross checking using different models
(including opus-5, which AFAICS is the one producing more relevant
feedback ATM).

The bottom line is that sashiko nipa is/should be the most relevant
sashiko instance to look at.

/P