Re: [PATCH 0/4] ima: support fs-verity signatures stored as

Mimi Zohar
2021-11-30T12:56:35Z

On Mon, 2021-11-29 at 18:36 -0800, Eric Biggers wrote:
> On Mon, Nov 29, 2021 at 12:00:53PM -0500, Mimi Zohar wrote:
> > Support for fs-verity file digests in IMA was discussed from the beginning,
> > prior to fs-verity being upstreamed[1,2]. This patch set adds signature
> > verification support based on the fs-verity file digest. Both the
> > file digest and the signature must be included in the IMA measurement list
> > in order to disambiguate the type of file digest.
> >
> > [1] https://events19.linuxfoundation.org/wp-content/uploads/2017/11/fs-verify_Mike-Halcrow_Eric-Biggers.pdf
> > [2] Documentation/filesystems/fsverity.rst
> >
> > Mimi Zohar (4):
> > fs-verity: define a function to return the integrity protected file
> > digest
> > ima: define a new signature type named IMA_VERITY_DIGSIG
> > ima: limit including fs-verity's file digest in measurement list
> > ima: support fs-verity file digest based signatures
> >
> > fs/verity/fsverity_private.h | 6 ---
> > fs/verity/measure.c | 49 +++++++++++++++++++++++
> > include/linux/fsverity.h | 17 ++++++++
> > security/integrity/ima/ima.h | 3 +-
> > security/integrity/ima/ima_api.c | 23 ++++++++++-
> > security/integrity/ima/ima_appraise.c | 9 ++++-
> > security/integrity/ima/ima_main.c | 7 +++-
> > security/integrity/ima/ima_template_lib.c | 3 +-
> > security/integrity/integrity.h | 1 +
> > 9 files changed, 107 insertions(+), 11 deletions(-)
>
> I left some comments, but this generally looks like the right approach.
> However, I'm not an expert in IMA, so it's hard for me to review the IMA parts.

Thank you for the quick review!

>
> Can you add documentation for this feature?

Yes, of course. Originally I assumed the fs-verity support would be a
lot more complicated, but to my pleasant surprise by limiting the IMA
fsverity support to just signatures and requiring the file signature be
included in the IMA measurement list, it's a lot simpler than expected.
As there aren't any IMA policy changes, I'm just thinking about where
to document it.

thanks,

Mimi