linux-kernel - Re: [PATCH v2 0/3] block: add queue-private command filter, editable via sysfs

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Message-ID: <506D60FC.7090801@redhat.com>
Date:	Thu, 04 Oct 2012 12:12:12 +0200
From:	Paolo Bonzini <pbonzini@...hat.com>
To:	unlisted-recipients:; (no To-header on input)
CC:	linux-kernel@...r.kernel.org, Tejun Heo <tj@...nel.org>,
	James Bottomley <James.Bottomley@...senPartnership.com>,
	Jens Axboe <axboe@...nel.dk>,
	Ric Wheeler <rwheeler@...hat.com>,
	Alan Cox <alan@...rguk.ukuu.org.uk>, linux-scsi@...r.kernel.org
Subject: Re: [PATCH v2 0/3] block: add queue-private command filter, editable
 via sysfs

Il 25/09/2012 17:30, Paolo Bonzini ha scritto:
> The set of use cases for SG_IO is quite variable that no single filter can
> accomodate all of them.  The current filter is tailored very much to
> CD burning, and includes many MMC-specific commands that may have
> other meanings in different standards.  Someone may want to remove
> those commands; at the same time, people that trust their users may
> want to add persistent reservations, trim/discard, or even access to
> vendor-specific commands.
> 
> Filters used to be mutable via sysfs, but the implementation was
> never enabled.  Add it back, and let the admin set this up per device.
> 
> A simple bitmap does not let you do things like enabling command A with
> option B on a specific device for a certain block range.  However, the
> question is really whether this is needed---in fact, neither of the known
> uses for the filtering need it.
> 
> In one use case, the administrator then needs the ability to configure
> devices easily, for example to be much more restrictive on non-MMC
> devices.  It must be done with the same tools it uses for other aspects
> of the policy---which will be a combination of DAC (Unix permissions and
> ACLs) and sysfs.  Different SCSI standards may give different meanings
> for the same byte value, but a simple bitmap is enough for this.
> 
> In the virtualization case, the problem is really that you want to
> pass through everything or almost everything, while still running as
> confined as possible (i.e. CAP_SYS_RAWIO is not a choice).  But in this
> case a more complex filtering can be done just as easily in userspace,
> in the virtual machine monitor.  While the userspace filter can be
> subverted if the guest can escape the QEMU jail, the bitmap still lets
> you block some commands at the kernel level if really necessary.
> 
> One alternative is a ioctl to disable the filter altogether, to be
> used together with SCM_RIGHTS file descriptor passing.  This works in
> the virtualization case but not for policy decisions.  So this patch
> series provides the sysfs knob.  It is a tweaked revert of commit 018e044
> (block: get rid of queue-private command filter, 2009-06-26).
> 
> Please review!
> 
> Paolo
> 
> v1->v2: add OOM and capability checks
> 
> Paolo Bonzini (3):
>   block: add back queue-private command filter
>   scsi: create an all-zero filter for scanners
>   block: add back command filter modification via sysfs
> 
>  Documentation/block/queue-sysfs.txt |   16 +++++
>  block/Kconfig                       |   10 +++
>  block/blk-sysfs.c                   |   43 +++++++++++++
>  block/bsg.c                         |    2 +-
>  block/scsi_ioctl.c                  |  117 +++++++++++++++++++++++++++++++----
>  drivers/scsi/scsi_scan.c            |    6 ++-
>  drivers/scsi/sg.c                   |    7 +-
>  include/linux/blkdev.h              |   31 +++++++++-
>  8 files changed, 213 insertions(+), 19 deletions(-)
> 
> --
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> 

Ping?

Tejun, Jens, anyone else, any hope that this gets in 3.7?

Paolo
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