[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/ (local))
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.

Best regards, nxhack