CVE-2026-99041ip6_gre: remove obsolete ERSPAN PMTU update

Official description

In the Linux kernel, the following vulnerability has been resolved: ip6_gre: remove obsolete ERSPAN PMTU update A tc tunnel_key action can attach a METADATA_IP_TUNNEL dst to an skb, and mirred can redirect it to a native ip6erspan device. The legacy PMTU update in ip6erspan_tunnel_xmit() treats that metadata dst as a route. Since it has no output device, dst_dev(dst)->mtu dereferences NULL. On v7.2 with KASAN, an initial UID/GID 65534 process with CapEff 0 used self-created user and network namespaces to trigger: KASAN: null-ptr-deref RIP: ip6erspan_tunnel_xmit+0x10fc/0x2cc0 Kernel panic - not syncing: Fatal exception in interrupt The update is obsolete. Commit fe1a4ca0a2b7 ("ip6_gre: process toobig in a better way") changed IPv6 GRE Too Big handling to update the underlay route and removed the equivalent block from __gre6_xmit(). ip6_tnl_xmit() then propagates the underlay PMTU to the overlay route. Remove the stale ERSPAN copy and its now-unused dst variable. This eliminates the metadata-dst dereference and keeps ERSPAN aligned with IPv6 GRE PMTU handling.

Affected packages & fixed versions

Affected products (as reported)

References

• https://git.kernel.org/stable/c/2e151c74bcc53e3ed313bd1c21b0d5bb442edbc0
• https://git.kernel.org/stable/c/ba72ed1c8476ce68eb7152dfcbc5330cefcbaa91
• https://git.kernel.org/stable/c/b14a682ad7d45345701e08f9279d483a1da8b36c
• https://git.kernel.org/stable/c/f5b143f4cd3fb7673df8d727550478a4b762908a
• https://git.kernel.org/stable/c/2d06cb25a497d3a7034ef9d172626c2d6620a0f1
• https://git.kernel.org/stable/c/8f27260b989f488760289276377db24fbfb20bfa
• https://git.kernel.org/stable/c/8bc60db48e8cba35488bbd6e1f94aa990afa275a