Re: [PATCH net] ip6_tunnel: use skb_vlan_inet_prepare() in __ip6_tnl_rcv()

[Greg Kroah-Hartman <gregkh@linuxfoundation.org>]

On Tue, Feb 10, 2026 at 01:56:14PM +0100, Eric Dumazet wrote:
> On Tue, Feb 10, 2026 at 1:42 PM Ricardo B. Marlière <rbm@suse.com> wrote:
> >
> > On Fri Jan 30, 2026 at 9:00 AM -03, Eric Dumazet wrote:
> > > On Fri, Jan 30, 2026 at 5:15 AM Hirokazu MORIKAWA <morikw2@gmail.com> wrote:
> > >>
> > >> [REGRESSION] ip6_tunnel: IPv4 traffic broken in MAP-E/DS-Lite since
> > >> commit df5ffde96693
> > >>
> > >> Hi,
> > >> I am reporting a regression in the IPv6 tunneling stack (MAP-E and
> > >> DS-Lite) introduced in kernel 6.12.67.
> > >>
> > >> [Description] After upgrading the kernel from 6.12.66 to 6.12.67 in
> > >> the OpenWrt snapshot, IPv4 packets can no longer be sent to the
> > >> external network via MAP-E or DS-Lite interfaces.
> > >> [Environment]
> > >> * Hardware: FriendlyElec NanoPi R6C
> > >> * OS: OpenWrt snapshot
> > >> * Kernel version: 6.12.67 (Broken), 6.12.66 (Working)
> > >> * Protocol: MAP-E and DS-Lite
> > >> [Culprit] By bisecting/reverting individual commits, I have identified
> > >> that the following commit is responsible for this issue:
> > >> "ip6_tunnel: use skb_vlan_inet_prepare() in __ip6_tnl_rcv()" (Link to
> > >> the patch: https://lore.kernel.org/netdev/20260107163109.4188620-1-edumazet@google.com/)
> > >> Reverting this specific commit on top of kernel 6.12.67 restores
> > >> normal connectivity for both MAP-E and DS-Lite.
> > >> [Steps to reproduce]
> > >> 1. Set up a MAP-E or DS-Lite connection on kernel 6.12.67.
> > >> 2. Attempt to send IPv4 traffic (e.g., ping 8.8.8.8).
> > >> 3. The packets fail to reach the destination.
> > >
> > > Thanks for the report.
> > >
> > > Can you provide detailed instructions ?
> > >
> > > Apparently none of our selftests caught the issue, it would be great to add one.
> >
> > Perhaps l2_tos_ttl_inherit.sh [1]? I've seen a timeout in this test that
> > went away after testing commit 9990ddf47d41 ("net: tunnel: make
> > skb_vlan_inet_prepare() return drop reasons") like mentioned here:
> >
> > https://lore.kernel.org/netdev/DGAR3PO1D33S.1TI7W7U4SPTOG@suse.com/
> >
> > It seems that that commit 81c734dae203 ("ip6_tunnel: use
> > skb_vlan_inet_prepare() in __ip6_tnl_rcv()") uses the new
> > skb_vlan_inet_prepare added in v6.13, which broke 6.12.
> 
> Greg Kroah-Hartman backported my patch to 6.12 LTS, but forgot that a
> prior patch
> from Menglong Dong inverted the skb_vlan_inet_prepare() return code.
> 
> Greg, can you backport the following to 6.12 LTS ?
> 
> Thanks.
> 
> commit 9990ddf47d4168088e2246c3d418bf526e40830d
> Author: Menglong Dong <menglong8.dong@gmail.com>
> Date:   Wed Oct 9 10:28:21 2024 +0800
> 
>     net: tunnel: make skb_vlan_inet_prepare() return drop reasons
> 
>     Make skb_vlan_inet_prepare return the skb drop reasons, which is just
>     what pskb_may_pull_reason() returns. Meanwhile, adjust all the call of
>     it.
> 
>     Signed-off-by: Menglong Dong <dongml2@chinatelecom.cn>
>     Reviewed-by: Simon Horman <horms@kernel.org>
>     Signed-off-by: David S. Miller <davem@davemloft.net>

Sure, will do after this next round of releases goes out.

greg k-h