DM for detecting bad disks was: dm-crypt, new IV and standards

[Mike Fedyk]

Pavel Machek wrote:
> Hi!
>
>
> > > > Well, CTR mode is not recommended for encrypted file systems because it is very
> > > > easy to corrupt single bits, bytes, blocks, etc without an integrity check.
> > > > If we add a MAC, then any mode of operation except ECB can be used for
> > > > encrypted file systems.
> > >
> > > what does "easy to corrupt" mean?  i haven't really seen disks generate
> > > bit errors ever.  this MAC means you'll need to write integrity data for
> > > every real write.  that really doesn't seem worth it...
> >
> > The difference between "_1,000,000" and "_8,000,000" is 1 bit.  If an
> > attacker knew enough about the layout of the filesystem (modify times on blocks,
> > etc) they could flip a single bit and change your _1Mil purchase order
> > approved by your boss to a _8Mil order.
>
>
> Hmm... long time ago I created crc loop device to catch
> faulty disks. If cryptoloop can do that for me... very good!

Yes, a crc, or some other very low overhead DM target would be great for 
this.  I haven't looked at DM too much. :( Does it already have 
something like this already?
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