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 09:48:28 -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, Paolo.

On Fri, Nov 02, 2012 at 03:35:30PM +0000, Alan Cox wrote:
> > >> That would be a change with respect to what we have now.  After
> > >> transferring a root-opened (better: CAP_SYS_RAWIO-opened) file
> > >> descriptor to an unprivileged process your SG_IO commands get
> > >> filtered.  So a ioctl is needed if you want to rely on SCM_RIGHTS.
> > > 
> > > 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.
> 
> In other contexts you inherit file handles via exec and having a "root
> opened so its special" model is bad. Historically it led to things like
> the rlogin/rsh hacks on SunOS and friends where a program run by the rsh
> daemon got a root opened socket as its stdin/out and could issue ifconfig
> ioctls on it at will.
> 
> Not a good model. Any removal of filters and passing them to a task
> should be explicit. The behaviour really ought to be to permit the
> intentional setting of explicit filters then passing them, not touch the
> default behaviour.

Yeah, well, then I guess it'll have to be a separate ioctl to switch
SG_IO for !root users.

Thanks.

-- 
tejun
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