Re: [PATCH net] ip6_tunnel: fix GRE6 segmentation

[David Ahern <dsahern@gmail.com>]

On 6/21/21 7:52 PM, Jakub Kicinski wrote:
> Commit 6c11fbf97e69 ("ip6_tunnel: add MPLS transmit support")
> moved assiging inner_ipproto down from ipxip6_tnl_xmit() to
> its callee ip6_tnl_xmit(). The latter is also used by GRE.
> 
> Since commit 38720352412a ("gre: Use inner_proto to obtain inner
> header protocol") GRE had been depending on skb->inner_protocol
> during segmentation. It sets it in gre_build_header() and reads
> it in gre_gso_segment(). Changes to ip6_tnl_xmit() overwrite
> the protocol, resulting in GSO skbs getting dropped.
> 
> Note that inner_protocol is a union with inner_ipproto,
> GRE uses the former while the change switched it to the latter
> (always setting it to just IPPROTO_GRE).
> 
> Restore the original location of skb_set_inner_ipproto(),
> it is unclear why it was moved in the first place.
> 
> Fixes: 6c11fbf97e69 ("ip6_tunnel: add MPLS transmit support")
> Signed-off-by: Jakub Kicinski <kuba@kernel.org>
> ---
>  net/ipv6/ip6_tunnel.c | 4 ++--
>  1 file changed, 2 insertions(+), 2 deletions(-)
> 

would be good to capture the GRE use case that found the bug and the
MPLS version as test cases under tools/testing/selftests/net. Both
should be doable using namespaces.