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

lists.openwall.net		lists / announce owl-users owl-dev john-users john-dev passwdqc-users yescrypt popa3d-users / oss-security kernel-hardening musl sabotage tlsify passwords / crypt-dev xvendor / Bugtraq Full-Disclosure linux-kernel linux-netdev linux-ext4 linux-hardening linux-cve-announce PHC
Open Source and information security mailing list archives

Hash Suite for Android: free password hash cracker in your pocket

[<prev] [next>] [<thread-prev] [thread-next>] [day] [month] [year] [list]

Message-ID: <20150617180921.7972345d@igors-macbook-pro.local>
Date:	Wed, 17 Jun 2015 18:09:21 +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 17:38:40 +0200
"Michael S. Tsirkin" <mst@...hat.com> wrote:

> On Wed, Jun 17, 2015 at 05:12:57PM +0200, Igor Mammedov wrote:
> > 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.
> > 
> 
> Of course it does not give out unlimited fds, there's a way
> for the sysadmin to specify the number of fds. Look at how libvirt
> uses vhost, it should become clear I think.
then it just means that tool has to take into account a new limits
to partition host in sensible manner.
Exposing limit as module parameter might be of help to tool for
getting/setting it in a way it needs.
--
To unsubscribe from this list: send the line "unsubscribe linux-kernel" in
the body of a message to majordomo@...r.kernel.org
More majordomo info at  http://vger.kernel.org/majordomo-info.html
Please read the FAQ at  http://www.tux.org/lkml/