In the Linux kernel, the following vulnerability has been resolved:
udp: skip L4 aggregation for UDP tunnel packets
If NETIFFGROFRAGLIST or NETIFFGROUDPFWD are enabled, and there are UDP tunnels available in the system, udpgroreceive() could end-up doing L4 aggregation (either SKBGSOUDPL4 or SKBGSOFRAGLIST) at the outer UDP tunnel level for packets effectively carrying and UDP tunnel header.
That could cause inner protocol corruption. If e.g. the relevant packets carry a vxlan header, different vxlan ids will be ignored/ aggregated to the same GSO packet. Inner headers will be ignored, too, so that e.g. TCP over vxlan push packets will be held in the GRO engine till the next flush, etc.
Just skip the SKBGSOUDPL4 and SKBGSOFRAGLIST code path if the current packet could land in a UDP tunnel, and let udpgroreceive() do GRO via udpsk(sk)->gro_receive.
The check implemented in this patch is broader than what is strictly needed, as the existing UDP tunnel could be e.g. configured on top of a different device: we could end-up skipping GRO at-all for some packets.
Anyhow, that is a very thin corner case and covering it will add quite a bit of complexity.
v1 -> v2: - hopefully clarify the commit message