linux-kernel - Re: setting up CDB filters in udev (was Re: [PATCH v2 0/3] block: add queue-private command filter, editable via sysfs)

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Date:	Fri, 2 Nov 2012 09:51:23 -0700
From:	Tejun Heo <tj@...nel.org>
To:	Paolo Bonzini <pbonzini@...hat.com>
Cc:	Ric Wheeler <rwheeler@...hat.com>,
	Petr Matousek <pmatouse@...hat.com>,
	Kay Sievers <kay@...hat.com>, Jens Axboe <axboe@...nel.dk>,
	linux-kernel@...r.kernel.org,
	"James E.J. Bottomley" <James.Bottomley@...senPartnership.com>
Subject: Re: setting up CDB filters in udev (was Re: [PATCH v2 0/3] block:
 add queue-private command filter, editable via sysfs)

Hey, Paolo.

On Fri, Nov 02, 2012 at 03:49:02PM +0100, Paolo Bonzini wrote:
> > Yeah, I get that it's a behavior change, but would that be a problem?
> 
> Worse, it's a potential security hole because previously you'd get
> filtering and now you wouldn't.
> 
> Considering that SCM_RIGHTS is usually used to transfer a file
> descriptor from a privileged process to an unprivileged one, I'd be very
> worried of that.

Yeah, I know it's a security thing, was wondering how bad it was.  So,
if we choose this, I guess we'll need an ioctl to switch userland
SG_IO filtering.

> > What disturbs me is that it's a completely new interface to userland
> > and at the same a very limited one at that.  So, yeah, it's
> > bothersome.  I personally would prefer SCM_RIGHTS behavior change +
> > hard coded filters per device class.
> 
> I think hard-coded filters are bad (I prefer to move policy to
> userspace), and SCM_RIGHTS without a ioctl is out of question, really.

No rule is really absolute.  To me, it seems the suggested in-kernel
per-device command code filter is both too big for the given problem
while being too limited for much beyond that.  So, if we can get away
with adding an ioctl, I personally think that would be a better
approach.

Thanks.

-- 
tejun
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