linux-kernel - Re: PING^7 (was Re: [PATCH v2 00/14] Corrections and customization of the SG

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Message-ID: <51A062B5.8040601@redhat.com>
Date:	Sat, 25 May 2013 09:05:25 +0200
From:	Paolo Bonzini <pbonzini@...hat.com>
To:	Christoph Hellwig <hch@...radead.org>
CC:	James Bottomley <James.Bottomley@...senPartnership.com>,
	Tejun Heo <tj@...nel.org>, Jens Axboe <axboe@...nel.dk>,
	lkml <linux-kernel@...r.kernel.org>,
	"linux-scsi@...r.kernel.org" <linux-scsi@...r.kernel.org>
Subject: Re: PING^7 (was Re: [PATCH v2 00/14] Corrections and customization
 of the SG_IO command whitelist (CVE-2012-4542))

Il 25/05/2013 07:27, Christoph Hellwig ha scritto:
> On Fri, May 24, 2013 at 09:35:02PM -0700, James Bottomley wrote:
>> I'll go along with this.  I'm also wondering what the problem would be
>> if we just allowed all commands on either CAP_SYS_RAWIO or opening the
>> device for write, so we just defer to the filesystem permissions and
>> restricted read only opens to the basic all device opcodes.
> 
> I've been out of this area for a bit, but the problem used to be that
> you could send destructive commands to a partition.  The right fix
> for that would be to not allow SG_IO on partitions at all, just
> wondering if anything would be broken by this.

Linus wanted to keep that for CAP_SYS_RAWIO.  We found two uses of SG_IO
on partitions: zfs-fuse used SYNCHRONIZE CACHE; some proprietary driver
used TEST UNIT READY.

Really, the solution is to make the bitmaps configurable in userspace.
It is no less secure than unpriv_sgio.  Then the kernel can be
configured at build-time to have either an MMC bitmap and a basic
whitelist of a dozen commands.  We can even avoid working around those
few conflicting opcodes; if you're paranoid you can just configure your
kernel right.

Paolo
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