UBUNTU-CVE-2026-98853: Medium severity ubuntu/linux vulnerability

In the Linux kernel, the following vulnerability has been resolved: net: gso: limit recursive IP-in-IP segmentation IP-in-IP GSO can re-enter inetgsosegment() or ipv6gsosegment() for each nested IP header. encaplevel tracks header bytes, not callback depth, so a deep chain can exhaust the kernel stack. Making inetgsosegment() stackable introduced unbounded IPv4 nesting; IPIP GSO/TSO later made the path reachable. The IPv6 stackable path was introduced separately and uses the same guard. Count IPv4 and IPv6 GSO handler entries in skbgsocb, initialized once per top-level GSO operation and preserved across GRE/UDP context changes. Use the existing IPTUNNELRECURSIONLIMIT for both handlers. The first five entries pass, and the sixth returns -EINVAL before dispatching another GSO callback.