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

On 8/17/26 8:42 AM, Ido Schimmel wrote:

On Thu, Aug 13, 2026 at 12:22:34AM +0800, Zhiling Zou wrote:

quoted

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 <redacted>

It wasn't reported by Vega.

quoted

Suggested-by: Ido Schimmel <idosch@nvidia.com>
Signed-off-by: Zhiling Zou <redacted>

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