CVE-2026-43057

In the Linux kernel, the following vulnerability has been resolved:

net: correctly handle tunneled traffic on IPV6_CSUM GSO fallback

NETIF_F_IPV6_CSUM only advertises support for checksum offload of

packets without IPv6 extension headers. Packets with extension

headers must fall back onto software checksumming. Since TSO

depends on checksum offload, those must revert to GSO.

The below commit introduces that fallback. It always checks

network header length. For tunneled packets, the inner header length

must be checked instead. Extend the check accordingly.

A special case is tunneled packets without inner IP protocol. Such as

RFC 6951 SCTP in UDP. Those are not standard IPv6 followed by

transport header either, so also must revert to the software GSO path.