CVE request: kernel: /sys/kernel/debug/acpi/custom_method can bypass module restrictions

[Kees Cook <kees () ubuntu com>]

Hi,

While CVE-2010-4347 covers the unprivileged to fully privileged escalation
issue, this interface still allows an unprivileged root user to gain
back all their capabilities.

Having a system with acpi and debugfs built into the kernel allows
a uid=0 user (without capabilities, e.g. in containers) to write to
arbitrary kernel memory, likely resulting in escalated capability
privileges[1], or unlocking an otherwise modules-disabled kernel by
changing /proc/sys/kernel/modules_disabled back to 0.

Thanks,

-Kees

[1] http://jon.oberheide.org/files/american-sign-language.c

-- 
Kees Cook
Ubuntu Security Team