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SubjectRe: [PATCH v1 4/5] ima: support fs-verity file digest based signatures
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On Thu, 2021-12-02 at 14:07 -0800, Eric Biggers wrote:
> On Thu, Dec 02, 2021 at 04:55:06PM -0500, Mimi Zohar wrote:
> > case IMA_VERITY_DIGSIG:
> > - fallthrough;
> > + set_bit(IMA_DIGSIG, &iint->atomic_flags);
> > +
> > + /*
> > + * The IMA signature is based on a hash of IMA_VERITY_DIGSIG
> > + * and the fs-verity file digest, not directly on the
> > + * fs-verity file digest. Both digests should probably be
> > + * included in the IMA measurement list, but for now this
> > + * digest is only used for verifying the IMA signature.
> > + */
> > + verity_digest[0] = IMA_VERITY_DIGSIG;
> > + memcpy(verity_digest + 1, iint->ima_hash->digest,
> > + iint->ima_hash->length);
> > +
> > + hash.hdr.algo = iint->ima_hash->algo;
> > + hash.hdr.length = iint->ima_hash->length;
>
> This is still wrong because the bytes being signed don't include the hash
> algorithm. Unless you mean for it to be implicitly always SHA-256? fs-verity
> supports SHA-512 too, and it may support other hash algorithms in the future.

The signature stored in security.ima is prefixed with a header
(signature_v2_hdr).

Mimi

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