CVE-2026-43390: nstree: tighten permission checks for listing

CVE-2026-43390: nstree: tighten permission checks for listing

[Greg Kroah-Hartman]

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

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

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

nstree: tighten permission checks for listing

Even privileged services should not necessarily be able to see other
privileged service's namespaces so they can't leak information to each
other. Use may_see_all_namespaces() helper that centralizes this policy
until the nstree adapts.

The Linux kernel CVE team has assigned CVE-2026-43390 to this issue.


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

	Issue introduced in 6.19 with commit 76b6f5dfb3fda76fce1f9990d6fa58adc711122b and fixed in 6.19.9 with commit 0abd81645fc95ec6a9d4e4813000f22c5efc0ff4
	Issue introduced in 6.19 with commit 76b6f5dfb3fda76fce1f9990d6fa58adc711122b and fixed in 7.0 with commit 8d76afe84fa2babf604b3c173730d4d2b067e361

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-2026-43390
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:
	kernel/nstree.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/0abd81645fc95ec6a9d4e4813000f22c5efc0ff4
	https://git.kernel.org/stable/c/8d76afe84fa2babf604b3c173730d4d2b067e361