CVE-2026-80929: sysctl: move the "cad_pid" entry from pid_table[] to kern_reboot_table[]

CVE-2026-80929: sysctl: move the "cad_pid" entry from pid_table[] to kern_reboot_table[]

[Greg Kroah-Hartman]

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

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

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

sysctl: move the "cad_pid" entry from pid_table[] to kern_reboot_table[]

cad_pid is global, and kill_cad_pid() is only used in the root namespace.

However, due to pid_table_root_permissions(), a non-root user can unshare
pid/user namespaces and modify it from the child namespace. This makes no
sense and is simply wrong.

Move it to kern_reboot_table[] where it logically belongs; this ensures
that only GLOBAL_ROOT_UID can read/modify this sysctl.

Note that this patch doesn't preserve "#ifdef CONFIG_PROC_SYSCTL" around
the "cad_pid"; CONFIG_PROC_SYSCTL selects CONFIG_SYSCTL, so it is always
set when kern_reboot_table[] is compiled.

The Linux kernel CVE team has assigned CVE-2026-80929 to this issue.


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

	Issue introduced in 6.17 with commit e054bcbe7e7af2baad3752f1a4916a7fffc0457e and fixed in 6.18.50 with commit e8527de7fea191fda704792a56081f9009aeec37
	Issue introduced in 6.17 with commit e054bcbe7e7af2baad3752f1a4916a7fffc0457e and fixed in 7.2.4 with commit a09bc4eaa67e1a72df3b6d0beb3afeef1e1fdfcd
	Issue introduced in 6.17 with commit e054bcbe7e7af2baad3752f1a4916a7fffc0457e and fixed in 7.3-rc1 with commit 7170ca01623b399c97f2ae9d3e228badc1f25ea3

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-2026-80929
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/pid.c
	kernel/reboot.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/e8527de7fea191fda704792a56081f9009aeec37
	https://git.kernel.org/stable/c/a09bc4eaa67e1a72df3b6d0beb3afeef1e1fdfcd
	https://git.kernel.org/stable/c/7170ca01623b399c97f2ae9d3e228badc1f25ea3