linux-kernel - Re: CVE-2024-46839: workqueue: Improve scalability of workqueue watchdog touch

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Message-ID: <2024100142-trespass-likewise-015a@gregkh>
Date: Tue, 1 Oct 2024 15:53:59 +0200
From: Greg Kroah-Hartman <gregkh@...uxfoundation.org>
To: Michal Hocko <mhocko@...e.com>
Cc: Petr Mladek <pmladek@...e.com>, cve@...nel.org,
	linux-kernel@...r.kernel.org, linux-cve-announce@...r.kernel.org,
	Srikar Dronamraju <srikar@...ux.vnet.ibm.com>,
	Nicholas Piggin <npiggin@...il.com>,
	"Paul E. McKenney" <paulmck@...nel.org>, Tejun Heo <tj@...nel.org>,
	Sasha Levin <sashal@...nel.org>,
	Michal Koutný <mkoutny@...e.com>
Subject: Re: CVE-2024-46839: workqueue: Improve scalability of workqueue
 watchdog touch

On Tue, Oct 01, 2024 at 11:07:49AM +0200, Michal Hocko wrote:
> On Tue 01-10-24 10:22:51, Greg KH wrote:
> > On Tue, Oct 01, 2024 at 10:02:02AM +0200, Petr Mladek wrote:
> > > On Fri 2024-09-27 14:40:07, Greg Kroah-Hartman wrote:
> > > > Description
> > > > ===========
> > > > 
> > > > In the Linux kernel, the following vulnerability has been resolved:
> > > > 
> > > > workqueue: Improve scalability of workqueue watchdog touch
> > > > 
> > > > On a ~2000 CPU powerpc system, hard lockups have been observed in the
> > > > workqueue code when stop_machine runs (in this case due to CPU hotplug).
> > > 
> > > I believe that this does not qualify as a security vulnerability.
> > > Any hotplug is a privileged operation.
> > 
> > Really?  I see that happen on many embedded systems all the time, they
> > add/remove CPUs while the device runs/sleeps constantly.
> 
> This is a powerpc specific fix. Other architectures are not affected.
>  
> > Now to be fair, right now an "embedded system" usually doesn't have 2000
> > cpus, but what's wrong with marking this real bugfix as a vulnerability
> > resolution?
> 
> Yes, this is indeed a scalability fix for huge systems with a lot of
> CPUs anybody owning those systems was simply not able to use memory
> hotplug without seeing those hard lockup messages. The system is not
> really locked up. The progress of the hotplug operation is just utterly
> slow. Calling this a vulnerability is a stretch IMHO. 
> 
> The only potential attack vector is to have machine configured to panic
> on hard lockups on those huge ppc systems and allow cpu hotremove to an
> adversary which in itsels seems like a very bad idea anyway because
> availability of such a system is then effectively compromised.

Ok, now rejected, thanks.

greg k-h