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

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Date:	Sat, 25 May 2013 03:11:18 -0400
From:	Christoph Hellwig <hch@...radead.org>
To:	Paolo Bonzini <pbonzini@...hat.com>
Cc:	Christoph Hellwig <hch@...radead.org>,
	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))

On Sat, May 25, 2013 at 09:05:25AM +0200, Paolo Bonzini wrote:
> > 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.

Keep it simple.  Allowing SG_IO for CAP_SYS_RAWIO probably is fine,
allowing it for permissions only clearly isn't. All the per-command
filetering is just complete bullshit and the kind of bloat that
eventually will make Linux unmaintainable.

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