Re: CVE-2021-47090: mm/hwpoison: clear MF_COUNT_INCREASED before retrying get_any_page()

[Michal Hocko]

On Tue 05-03-24 22:20:17, Greg KH wrote:
> On Tue, Mar 05, 2024 at 07:45:04PM +0100, Michal Hocko wrote:
> > On Mon 04-03-24 19:11:17, Greg KH wrote:
> > > Description
> > > ===========
> > > 
> > > In the Linux kernel, the following vulnerability has been resolved:
> > > 
> > > mm/hwpoison: clear MF_COUNT_INCREASED before retrying get_any_page()
> > 
> > I would like to dispute this CVE. The interface is behind CAP_SYSADMIN
> > and allowing access to this to any untrusted party is risking serious
> > troubles. This is a testing only feature.
> 
> This fixes a weakness in the kernel, one that is allowed to crash it,
> why isn't that a good thing to have a CVE entry for?  Are we saying that
> all VM_BUG_ON_PAGE() instances should not be accounted for?  That's not
> what the config option for CONFIG_DEBUG_VM says, it just says it will
> affect performance.

I wouldn't personaly recommend anybody using CONFIG_DEBUG_VM=y in
production. But I am not questioning if somebody does that. This is
not really what I am objecting to. Hwpoisoning or soft offlining is not
aimed for other than testing purposes. Things can go wrong during
these oprations.

If you insist this still qualifies as a vulnaribility/weakness fix then
I would propose a new category pig-with-a-lipstick-CVE.

> Also /sys/devices/system/memory/soft_offline_page doesn't say "can crash
> the system", so it should work properly, even if an admin uses it, it
> shouldn't shut the box down.

I agree that Documentation/ABI/testing/sysfs-memory-page-offline would
benefit from an update. Documentation/admin-guide/mm/memory-hotplug.rst
is explicit about this being a testing feature.
-- 
Michal Hocko
SUSE Labs