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

[Tejun Heo <tj@kernel.org>]

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