From: Paolo Bonzini <pbonzini@redhat.com>
To: Tejun Heo <tj@kernel.org>
Cc: "James E.J. Bottomley" <JBottomley@parallels.com>,
Jens Axboe <axboe@kernel.dk>, lkml <linux-kernel@vger.kernel.org>,
"linux-scsi@vger.kernel.org" <linux-scsi@vger.kernel.org>
Subject: Re: PING^7 (was Re: [PATCH v2 00/14] Corrections and customization of the SG_IO command whitelist (CVE-2012-4542))
Date: Fri, 24 May 2013 10:31:34 +0200 [thread overview]
Message-ID: <519F2566.2000008@redhat.com> (raw)
In-Reply-To: <CAOS58YODjkSF=V7wADqbn_z8c6bmj=r03hWxEs5B1O+1cd0n6g@mail.gmail.com>
Il 24/05/2013 10:02, Tejun Heo ha scritto:
> On Fri, May 24, 2013 at 4:13 PM, Paolo Bonzini <pbonzini@redhat.com> wrote:
>>> The same filtering table being applied to different classes of
>>> hardware is a software bug, but my point is that the practive
>>> essentially entrusts non-insignificant part of security enforcement to
>>> the hardware itself. The variety of hardware in question is very wide
>>> and significant portion has historically been known to be flaky.
>>
>> Unproven theory, and contradicted by actual practice. Bugs are more
>> common in the handling of borderline conditions, not in the handling of
>> unimplemented commands.
>>
>> If you want to be secure aginst buggy firmware, the commands you have to
>> block are READ and WRITE. Check out the list of existing USB quirks.
>
> Well, I'd actually much prefer disabling CDB whitelisting for all !MMC
> devices if at all possible. You're basically arguing that because what
> we have is already broken, it should be okay to break it further.
> Also, RW commands having more quirks doesn't necessarily indicate that
> they tend to be more broken. They just get hammered on a lot in
> various ways so problems on those commands tend to be more noticeable.
I agree intuition may not count, and it's perfectly possible that
firmware writers forgot a "break;" or put the wrong location in a jump
table, so that unimplemented commands give interesting results.
However, the _fact_ is that this might happen anyway with the buttload
of commands that are already enabled by the whitelist and that most
disks will never implement.
>> You need to allow more commands.
>> The count-me-out knob allows all commands.
>> You cannot always allow all commands.
>> Ergo, you cannot always use the count-me-out knob.
>
> The thing is that both approaches aren't perfect here so you can make
> similar type of argument from the other side. If the system wants to
> give out raw hardware access to VMs, requiring it to delegate the
> device fully could be reasonable.
No, it is not unfortunately. Allowing to do discards is one thing,
allowing to disrupt the settings of a SAN is another. You can only
delegate the device fully in these cases:
(a) of course, if the guest is trusted;
(b) if QEMU is running as a confined user, then you can get by with a
userspace whitelist. (Otherwise you're just a ptrace away from
arbitrary access, as you pointed out).
Unfortunately, there are _real_ problems that this patches fix, such as
log spews due to blocked commands, and these happen even if neither of
the above conditions is true.
Is there anything else I can do? Sure, I can check for the presence of
the whitelist and hack the VPD pages to hide features that I know the
whitelist will block. Is it the right thing to do? In my opinion no.
It makes no sense to have raw device access _disable_ features compared
to emulation.
> Not ideal but widening direct
> command access by default is pretty nasty too.
I actually agree, and that's why I'm trying to balance the widening and
restricting.
Paolo
next prev parent reply other threads:[~2013-05-24 8:31 UTC|newest]
Thread overview: 73+ messages / expand[flat|nested] mbox.gz Atom feed top
2013-02-06 15:15 [PATCH v2 00/14] Corrections and customization of the SG_IO command whitelist (CVE-2012-4542) Paolo Bonzini
2013-02-06 15:15 ` [PATCH v2 01/14] sg_io: pass request_queue to blk_verify_command Paolo Bonzini
2013-02-06 15:15 ` [PATCH v2 02/14] sg_io: reorganize list of allowed commands Paolo Bonzini
2013-02-06 15:15 ` [PATCH v2 03/14] sg_io: use different default filters for each device class Paolo Bonzini
2013-02-06 15:15 ` [PATCH v2 04/14] sg_io: resolve conflicts between commands assigned to multiple classes (CVE-2012-4542) Paolo Bonzini
2013-02-06 15:15 ` [PATCH v2 05/14] sg_io: whitelist a few more commands for rare & obsolete device types Paolo Bonzini
2013-02-06 15:15 ` [PATCH v2 06/14] sg_io: whitelist another command for multimedia devices Paolo Bonzini
2013-02-06 15:15 ` [PATCH v2 07/14] sg_io: whitelist a few more commands for media changers Paolo Bonzini
2013-02-06 15:15 ` [PATCH v2 08/14] sg_io: whitelist a few more commands for tapes Paolo Bonzini
2013-02-06 15:15 ` [PATCH v2 09/14] sg_io: whitelist a few more commands for disks Paolo Bonzini
2013-02-06 15:15 ` [PATCH v2 10/14] sg_io: whitelist a few obsolete commands Paolo Bonzini
2013-02-06 15:15 ` [PATCH v2 11/14] sg_io: mark blk_set_cmd_filter_defaults as __init Paolo Bonzini
2013-02-06 15:15 ` [PATCH v2 12/14] sg_io: remove remnants of sysfs SG_IO filters Paolo Bonzini
2013-02-06 15:16 ` [PATCH v2 13/14] sg_io: introduce unpriv_sgio queue flag Paolo Bonzini
2013-02-06 15:16 ` [PATCH v2 14/14] sg_io: use unpriv_sgio to disable whitelisting for scanners Paolo Bonzini
2013-02-13 8:32 ` [PATCH v2 00/14] Corrections and customization of the SG_IO command whitelist (CVE-2012-4542) Paolo Bonzini
2013-02-13 15:35 ` Douglas Gilbert
2013-02-13 15:48 ` Paolo Bonzini
2013-02-20 16:12 ` Paolo Bonzini
2013-03-22 22:30 ` PING^2 " Paolo Bonzini
2013-04-04 18:18 ` PING^3 " Paolo Bonzini
2013-04-17 12:26 ` PING^4 aka The Jon Corbet Effect " Paolo Bonzini
2013-04-27 13:31 ` PING^5 aka New ways to attract attentions " Paolo Bonzini
2013-05-06 20:43 ` PING^6 " Paolo Bonzini
2013-05-22 6:35 ` PING^7 (was Re: [PATCH v2 00/14] Corrections and customization of the SG_IO command whitelist (CVE-2012-4542)) Paolo Bonzini
2013-05-22 9:32 ` Tejun Heo
2013-05-22 9:53 ` Paolo Bonzini
2013-05-22 10:02 ` Tejun Heo
2013-05-22 10:23 ` Paolo Bonzini
2013-05-22 12:07 ` James Bottomley
2013-05-22 14:07 ` Paolo Bonzini
2013-05-22 16:31 ` Paolo Bonzini
2013-05-22 13:41 ` Tejun Heo
2013-05-22 14:12 ` Paolo Bonzini
2013-05-22 14:30 ` Tejun Heo
2013-05-22 15:00 ` Paolo Bonzini
2013-05-22 19:30 ` Tejun Heo
2013-05-22 21:18 ` Paolo Bonzini
2013-05-22 22:17 ` Tejun Heo
2013-05-23 0:54 ` Tejun Heo
2013-05-23 7:45 ` Paolo Bonzini
2013-05-23 9:02 ` Tejun Heo
2013-05-23 9:47 ` Paolo Bonzini
2013-05-24 1:44 ` Tejun Heo
2013-05-24 7:13 ` Paolo Bonzini
2013-05-24 8:02 ` Tejun Heo
2013-05-24 8:31 ` Paolo Bonzini [this message]
2013-05-24 9:07 ` Tejun Heo
2013-05-24 9:45 ` Paolo Bonzini
2013-05-24 22:20 ` Tejun Heo
2013-05-25 4:35 ` James Bottomley
2013-05-25 5:27 ` Christoph Hellwig
2013-05-25 7:05 ` Paolo Bonzini
2013-05-25 7:11 ` Christoph Hellwig
2013-05-25 7:21 ` Paolo Bonzini
2013-06-21 11:57 ` Christoph Hellwig
2013-05-25 8:37 ` Tejun Heo
2013-05-25 11:14 ` Paolo Bonzini
2013-05-25 12:48 ` Tejun Heo
2013-05-25 12:56 ` Paolo Bonzini
2013-05-22 15:03 ` Theodore Ts'o
2013-05-22 15:53 ` Paolo Bonzini
2013-05-22 16:32 ` Martin K. Petersen
2013-05-22 17:00 ` Paolo Bonzini
2013-05-22 18:11 ` Theodore Ts'o
2013-05-22 19:37 ` Paolo Bonzini
2013-05-22 20:19 ` Theodore Ts'o
2013-05-22 20:36 ` Paolo Bonzini
2013-05-25 3:54 ` Vladislav Bolkhovitin
2013-05-28 20:25 ` Martin K. Petersen
2013-05-29 6:12 ` Vladislav Bolkhovitin
2013-05-22 20:39 ` Tejun Heo
2013-05-22 21:12 ` Paolo Bonzini
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