CVE-2026-46120ip6_gre: Use cached t->net in ip6erspan_changelink().

Official description

In the Linux kernel, the following vulnerability has been resolved: ip6_gre: Use cached t->net in ip6erspan_changelink(). After commit 5e72ce3e3980 ("net: ipv6: Use link netns in newlink() of rtnl_link_ops"), ip6erspan_newlink() correctly resolves the per-netns ip6gre hash via link_net. ip6erspan_changelink() was not converted in that series and still uses dev_net(dev), which diverges from the device's creation netns after IFLA_NET_NS_FD migration. This re-inserts the tunnel into the wrong per-netns hash. The original netns keeps a stale entry. When that netns is later destroyed, ip6gre_exit_rtnl_net() walks the stale entry, producing a slab-use-after-free reported by KASAN, followed by a kernel BUG at net/core/dev.c (LIST_POISON1) in unregister_netdevice_many_notify(). Reachable from an unprivileged user namespace (unshare --user --map-root-user --net). ip6gre_changelink() earlier in the same file already uses the cached t->net; only ip6erspan_changelink() has the wrong shape.

Affected packages & fixed versions

Affected products (as reported)

References

• https://git.kernel.org/stable/c/7bd0f2b162b426b343a114e1b329f0d8d14fdc6e
• https://git.kernel.org/stable/c/01b71ff2857d3598337de11e7840a8e3ff21553c
• https://git.kernel.org/stable/c/0fcf6731706f73494245a9c0d64f93bebf95bb51
• https://git.kernel.org/stable/c/eca62bb0569de4d43a4dac06a2092a9d4ca1d702
• https://git.kernel.org/stable/c/311fdd26eb4443d43b909cc67a10f3a5fd1b21b2
• https://git.kernel.org/stable/c/e70cfb40c3a99b232cd42c6a6a10f0d8e039dc82
• https://git.kernel.org/stable/c/cf7fc624329e76c6394653d12353e1d033adea91
• https://git.kernel.org/stable/c/1d324c2f43f70c965f25c58cc3611c779adbe47e
• https://cert-portal.siemens.com/productcert/html/ssa-784472.html