CVE-2026-80929

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.