Re: [PATCH 1/2] Fix sign_hash not observing the hashalgo argument

Patrick Uiterwijk
2021-01-07T15:14:42Z

On Thu, Jan 7, 2021 at 2:15 PM Vitaly Chikunov <vt@altlinux.org> wrote:
>
> On Thu, Jan 07, 2021 at 04:08:16PM +0300, Vitaly Chikunov wrote:
> > Patrick, Mimi,
> >
> > On Thu, Jan 07, 2021 at 07:24:43AM -0500, Mimi Zohar wrote:
> > > On Wed, 2021-01-06 at 10:43 +0100, Patrick Uiterwijk wrote:
> > > > This fixes sign_hash not using the correct algorithm for creating the
> > > > signature, by ensuring it uses the passed in variable value.
> > > >
> > > > Signed-off-by: Patrick Uiterwijk <patrick@puiterwijk.org>
> > >
> > > Thank you. This is a regression first introduced in commit
> > > 07e623b60848 ("ima-evm-utils: Convert sign_hash_v2 to EVP_PKEY API").
> >
> > Ah, when sign_hash() is used not via evmctl, but as a library
> > imaevm_params may be not set.
>
> Thinking about imaevm_params -- it's still belong to a library and
> extensively used in libimaevm.c, so I wonder if the fix is perfect.
> Since, now there is hash_algo and algo duplication which one to prefer
> and why?
>
> Maybe, it should be [also] set like keypass in sign_hash?

I had this exact diff as an initial version of this patch, but then
personally thought that because "hashalgo" is passed to sign_hash_v2
anyway, and sign_hash_v1 already prefers the argument (and ignores
imaevm_params.hash_algo), keeping this behaviour in sync is more
consistent.
With my patch, imaevm_params.hash_algo is only used in verify_hash_v2
and ima_calc_hash, both of which are primarily called by
ima_verify_signature which sets it, as a way to pass the argument
without having it explicit everywhere.

>
> int sign_hash(const char *hashalgo, const unsigned char *hash, int size, const char *keyfile, const char *keypass, unsigned char *sig)
> {
> if (keypass)
> imaevm_params.keypass = keypass;
>
> + if (hashalgo)
> + imaevm_params.hash_algo = hashalgo;
>
> return imaevm_params.x509 ?
> sign_hash_v2(hashalgo, hash, size, keyfile, sig) :
> sign_hash_v1(hashalgo, hash, size, keyfile, sig);
> }
>
>