On Fri, Mar 01, 2024 at 10:19:13AM +0100, Roberto Sassu wrote:

On Wed, 2024-02-21 at 15:24 -0600, Seth Forshee (DigitalOcean) wrote:

quoted

Support the new fscaps security hooks by converting the vfs_caps to raw
xattr data and then handling them the same as other xattrs.

Hi Seth

I started looking at this patch set.

The first question I have is if you are also going to update libcap
(and also tar, I guess), since both deal with the raw xattr.

From IMA/EVM perspective (Mimi will add on that), I guess it is
important that files with a signature/HMAC continue to be accessible
after applying this patch set.

Looking at the code, it seems the case (if I understood correctly,
vfs_getxattr_alloc() is still allowed).

To be sure that everything works, it would be really nice if you could
also extend our test suite:

https://github.com/mimizohar/ima-evm-utils/blob/next-testing/tests/portable_signatures.test

and

https://github.com/mimizohar/ima-evm-utils/blob/next-testing/tests/evm_hmac.test


The first test we would need to extend is check_cp_preserve_xattrs,
which basically does a cp -a. We would need to set fscaps in the
origin, copy to the destination, and see if the latter is accessible.

I would also extend:

check_tar_extract_xattrs_different_owner
check_tar_extract_xattrs_same_owner
check_metadata_change
check_evm_revalidate
check_evm_portable_sig_ima_appraisal
check_evm_portable_sig_ima_measurement_list

It should not be too complicated. The purpose would be to exercise your
code below.


Regarding the second test, we would need to extend just check_evm_hmac.


Just realized, before extending the tests, it would be necessary to
modify also evmctl.c, to retrieve fscaps through the new interfaces,
and to let users provide custom fscaps the HMAC or portable signature
is calculated on.

While request for tests are obviously fine they should be added by the
respective experts for IMA/EVM in this case. I don't think it's
appropriate to expect Seth to do that especially because you seem to
imply that you currently don't have any tests for fscaps at all. We're
always happy to test things and if that'd be adding new IMA/EVM specific
features than it would be something to discuss but really we're
refactoring so the fact that you don't have tests we can run is not the
fault of this patchset and IMA/EVM is just a small portion of it.