CVE-2026-52909: ip6_vti: set netns_immutable on the fallback device.

CVE-2026-52909: ip6_vti: set netns_immutable on the fallback device.

[Greg Kroah-Hartman]

From: Greg Kroah-Hartman <gregkh@kernel.org>

Description
===========

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

ip6_vti: set netns_immutable on the fallback device.

john1988 and Noam Rathaus reported that vti6_init_net() does not set the
netns_immutable flag on the per-netns fallback tunnel device (ip6_vti0).

Other similar tunnel drivers (like ip6_tunnel, sit, ip6_gre, and ip_tunnel)
correctly set this flag during their fallback device initialization to
prevent them from being moved to another network namespace.

The Linux kernel CVE team has assigned CVE-2026-52909 to this issue.


Affected and fixed versions
===========================

	Issue introduced in 3.15 with commit 61220ab349485d911083d0b7990ccd3db6c63297 and fixed in 6.18.36 with commit ecf8904067dcba0dad86ece80874841e60317885
	Issue introduced in 3.15 with commit 61220ab349485d911083d0b7990ccd3db6c63297 and fixed in 7.0.13 with commit dcdce3bc9f08026ff3739ee7339e1bef526fc5f3
	Issue introduced in 3.15 with commit 61220ab349485d911083d0b7990ccd3db6c63297 and fixed in 7.1 with commit d289d5307762d1838aaece22c6b6fcad9e8865f9

Please see https://www.kernel.org for a full list of currently supported
kernel versions by the kernel community.

Unaffected versions might change over time as fixes are backported to
older supported kernel versions.  The official CVE entry at
	https://cve.org/CVERecord/?id=CVE-2026-52909
will be updated if fixes are backported, please check that for the most
up to date information about this issue.


Affected files
==============

The file(s) affected by this issue are:
	net/ipv6/ip6_vti.c


Mitigation
==========

The Linux kernel CVE team recommends that you update to the latest
stable kernel version for this, and many other bugfixes.  Individual
changes are never tested alone, but rather are part of a larger kernel
release.  Cherry-picking individual commits is not recommended or
supported by the Linux kernel community at all.  If however, updating to
the latest release is impossible, the individual changes to resolve this
issue can be found at these commits:
	https://git.kernel.org/stable/c/ecf8904067dcba0dad86ece80874841e60317885
	https://git.kernel.org/stable/c/dcdce3bc9f08026ff3739ee7339e1bef526fc5f3
	https://git.kernel.org/stable/c/d289d5307762d1838aaece22c6b6fcad9e8865f9