linux-kernel - Re: CVE-2021-47090: mm/hwpoison: clear MF_COUNT_INCREASED before retrying get_any

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Date: Wed, 6 Mar 2024 08:40:10 +0000
From: Greg Kroah-Hartman <gregkh@...uxfoundation.org>
To: Michal Hocko <mhocko@...e.com>
Cc: cve@...nel.org, linux-kernel@...r.kernel.org
Subject: Re: CVE-2021-47090: mm/hwpoison: clear MF_COUNT_INCREASED before
 retrying get_any_page()

On Wed, Mar 06, 2024 at 09:06:42AM +0100, Michal Hocko wrote:
> 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.

Agreed, things can go wrong, but people use them for "reasons" otherwise
we wouldn't have those options in the kernel at all.  Because of that,
this "fix for a weakness" was given a CVE, that's all.

Again, we do not dictate use case, or severity at all, that's not our
role.

> 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.

The fact that I didn't even notice that is kind of proof that maybe
others might also miss it :)

thanks,

greg k-h