Re: [RFC][PATCH v3a 00/11] ima: support fs-verity digests and signatures (alternative)

[Eric Biggers]

On Thu, Jan 27, 2022 at 07:46:09PM +0100, Roberto Sassu wrote:
> I wanted to propose a different approach for handling fsverity digests and
> signatures, compared to:
> 
> https://lore.kernel.org/linux-integrity/20220126000658.138345-1-zohar@xxxxxxxxxxxxx/
> 
> In the original proposal, a new signature version has been introduced (v3)
> to allow the possibility of signing the digest of a more flexible data
> structure, ima_file_id, which could also include the fsverity file digest.
> 
> While the new signature type would be sufficient to handle fsverity file
> digests, the problem is that its format would not be compatible with the
> signature format supported by the built-in verification module in fsverity.
> The rpm package manager already has an extension to include fsverity
> signatures, with the existing format, in the RPM header.
> 
> Given that the fsverity signature is in the PKCS#7 format, IMA has already
> the capability of handling it with the existing code, more specifically the
> modsig code. It would be sufficient to provide to modsig the correct data
> to avoid introducing a new signature format.

I think it would be best to get people moved off of the fs-verity built-in
signatures, rather than further extend the use of it.  PKCS#7 is a pretty
terrible signature format.  The IMA one is better, though it's unfortunate that
IMA still relies on X.509 for keys.

- Eric