Re: Allow FUSE filesystems to provide out-of-band hashes to IMA

[Mimi Zohar <zohar@linux.ibm.com>]

On Mon, 2018-10-08 at 13:19 -0700, Matthew Garrett wrote:
> On Mon, Oct 8, 2018 at 4:25 AM Mimi Zohar <zohar@linux.ibm.com> wrote:
> > On Fri, 2018-10-05 at 12:25 -0700, Matthew Garrett wrote:

> > > I agree that using FUSE in general is incompatible with IMA's goals,
> > > but it's possible to configure systems where you can ensure that only
> > > trustworthy code is involved. In that scenario this patch improves
> > > performance without compromising security.
> >
> > If you trust a FUSE filesystem to not only behave properly, but also
> > to return file hashes, what is the value of measuring/appraising the
> > files?  Define a custom policy that doesn't measure/appraise files on
> > FUSE filesystems.
> 
> We trust that the filesystem will return us accurate binaries and
> hashes, but we don't the binaries themselves may not be trustworthy -
> we want the same level of audit trail associated with their execution
> that we'd have for something run off local disk. We could certainly
> rearchitect our filesystems to generate audit events themselves, but
> we'd be duplicating functionality that already exists in the kernel.

I'm really not comfortable with the FUSE filesystem calculating the
file hash being used by IMA.  Adding FUSE i_version support would have
been better, instead of returning the actual file hash.  Based on a
mount option and the i_version, the kernel could then decide whether
or not to limit re-calculating the file hash.

Mimi