On Mon, May 16, 2022 at 11:51:54AM -0700, Matthias Kaehlcke wrote:

'targets' are different types of DM mappings like 'linear' or 'verity'. A
device mapper table contains has one or more targets that define the mapping
of the blocks of the mapped device.

Having spelled that out I realize that the above check is wrong. It would
consider a device like this trusted:

0 10000000 linear 8:1
10000000 10001000 verity <params>

In the above case only a small part of the DM device would be backed by verity.

I think we want a table with a single entry that is a verity target.

Ah-ha! Okay, that's what I was worried about. Yes, a device made up
of only trusted verity targets should be the only trusted device. (So,
technically it could be more than 1 verity target, but each would need
to be trusted. Supporting that arrangement, though, may be overkill --
I would expect a 1:1 mapping as you suggest.

-- 
Kees Cook