Re: PING^7 (was Re: [PATCH v2 00/14] Corrections and customizationof the SG_IO command whitelist (CVE-2012-4542))

[Paolo Bonzini]

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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