linux-kernel - Re: [PATCH 3/5] vhost: support upto 509 memory regions

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Message-ID: <20150617171257.11fe405d@nial.brq.redhat.com>
Date:	Wed, 17 Jun 2015 17:12:57 +0200
From:	Igor Mammedov <imammedo@...hat.com>
To:	"Michael S. Tsirkin" <mst@...hat.com>
Cc:	Paolo Bonzini <pbonzini@...hat.com>, linux-kernel@...r.kernel.org,
	kvm@...r.kernel.org
Subject: Re: [PATCH 3/5] vhost: support upto 509 memory regions

On Wed, 17 Jun 2015 16:32:02 +0200
"Michael S. Tsirkin" <mst@...hat.com> wrote:

> On Wed, Jun 17, 2015 at 03:20:44PM +0200, Paolo Bonzini wrote:
> > 
> > 
> > On 17/06/2015 15:13, Michael S. Tsirkin wrote:
> > > > > Considering userspace can be malicious, I guess yes.
> > > > I don't think it's a valid concern in this case,
> > > > setting limit back from 509 to 64 will not help here in any way,
> > > > userspace still can create as many vhost instances as it needs
> > > > to consume memory it desires.
> > > 
> > > Not really since vhost char device isn't world-accessible.
> > > It's typically opened by a priveledged tool, the fd is
> > > then passed to an unpriveledged userspace, or permissions dropped.
> > 
> > Then what's the concern anyway?
> > 
> > Paolo
> 
> Each fd now ties up 16K of kernel memory.  It didn't use to, so
> priveledged tool could safely give the unpriveledged userspace
> a ton of these fds.
if privileged tool gives out unlimited amount of fds then it
doesn't matter whether fd ties 4K or 16K, host still could be DoSed.


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