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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Message-ID: <20121102173022.GA27843@mtj.dyndns.org>
Date:	Fri, 2 Nov 2012 10:30:22 -0700
From:	Tejun Heo <tj@...nel.org>
To:	Alan Cox <alan@...rguk.ukuu.org.uk>
Cc:	Paolo Bonzini <pbonzini@...hat.com>,
	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, Alan.

On Fri, Nov 02, 2012 at 05:21:45PM +0000, Alan Cox wrote:
> That also means that a normal app running as superuser for some reason
> would set its user filter and any accidentally inherited descriptors will
> be less dangerous as the are today. It also means a CAP_SYS_RAWIO capable
> app can still use filters itself as good programming practise.
> 
> It effectively means you have to deliberately and intentionally set up an
> 'inherited' extra rights case.

The last part, I agree, but in general I think what you're describing
is way too elaborate for the problem at hand.  It's like adding
arbitrary range-filter for /dev/sdX which can be overridden by
userland.  You sure can find use case for such thing if you try hard
enough, but it's way over-engineered nonetheless.  I don't think we're
addressing huge range and number of use cases here and would much
prefer to keep it as simple as possible.

 * Devices are given standard filter matching the device class.  Any
   !CAP_SYS_RAWIO user can only issue commands allowed by the filter.

 * CAP_SYS_RAWIO can issue an ioctl to disable the filter all
   accessors of the fd and transfer it.

That should be enough, no?

Thanks.

-- 
tejun
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