Subject: Re: [PATCH net-net 0/4] Increase the limit of tuntap queues

From: Jason Wang <[email-masked]>
Date: Mon, 24 Nov 2014 11:23:05 +0800

On 11/23/2014 06:46 PM, Michael S. Tsirkin wrote:
> On Wed, Nov 19, 2014 at 10:44:27PM +0200, Michael S. Tsirkin wrote:
>> > On Wed, Nov 19, 2014 at 03:16:28PM -0500, David Miller wrote:
>>> > > From: Pankaj Gupta <[email-masked]>
>>> > > Date: Tue, 18 Nov 2014 21:52:54 +0530
>>> > > 
>>>> > > > - Accept maximum number of queues as sysctl param so that any user space 
>>>> > > >   application like libvirt can use this value to limit number of queues. Also
>>>> > > >   Administrators can specify maximum number of queues by updating this sysctl
>>>> > > >   entry.
>>> > > 
>>> > > This is the only part I don't like.
>>> > > 
>>> > > Just let whoever has privileges to configure the tun device shoot
>>> > > themselves in the foot if they want to by configuring "too many"
>>> > > queues.
>>> > > 
>>> > > If the virtual entity runs itself out of resources by doing something
>>> > > stupid, it's purely their problem.
>> > 
>> > Well it will run host out of kernel, no?
> To clarify:
>
> At the moment attaching/detaching queues is an unpriveledged operation.
>
> Shouldn't we worry that an application can cause large
> allocations, and provide a way to limit these?

But creating new queues (TUNSETIFF) is privileged. There's no way for
unprivileged user to allocate more resources. So we are safe here?