net: gso: limit recursive IP-in-IP segmentation

Overview

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 inet_gso_segment() or ipv6_gso_segment() for each nested IP header. encap_level tracks header bytes, not callback depth, so a deep chain can exhaust the kernel stack. Making inet_gso_segment() 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 skb_gso_cb, initialized once per top-level GSO operation and preserved across GRE/UDP context changes. Use the existing IP_TUNNEL_RECURSION_LIMIT for both handlers. The first five entries pass, and the sixth returns -EINVAL before dispatching another GSO callback.

Affected

• Linux >= 3347c960295583eee3fd58e5c539fb1972fbc005 < c949646c900e879afce47df1b607fa320eb63bf2
• Linux >= 3347c960295583eee3fd58e5c539fb1972fbc005 < 006c8b834aed8b02bd8fb9fb05e9e7ead37d1763
• Linux 3.13

Remediation

Refer to the linked advisories for vendor-supplied fixes and affected version ranges.