Re: [PATCH v5 01/11] ima-evm-utils: Make sure sig buffer is always MAX_SIGNATURE_SIZE

[Vitaly Chikunov <vt@altlinux.org>]

On Thu, Jun 20, 2019 at 05:42:18PM -0400, Mimi Zohar wrote:
> On Tue, 2019-06-18 at 16:56 +0300, Vitaly Chikunov wrote:
> > Fix off-by-one error of the output buffer passed to sign_hash().
> > 
> > Signed-off-by: Vitaly Chikunov <vt@altlinux.org>
> > ---
> >  src/evmctl.c | 4 ++--
> >  1 file changed, 2 insertions(+), 2 deletions(-)
> > 
> > diff --git a/src/evmctl.c b/src/evmctl.c
> > index 15a7226..03f41fe 100644
> > --- a/src/evmctl.c
> > +++ b/src/evmctl.c
> > @@ -510,7 +510,7 @@ static int calc_evm_hash(const char *file, unsigned char *hash)
> >  static int sign_evm(const char *file, const char *key)
> >  {
> >  	unsigned char hash[MAX_DIGEST_SIZE];
> > -	unsigned char sig[MAX_SIGNATURE_SIZE];
> > +	unsigned char sig[MAX_SIGNATURE_SIZE + 1];
> >  	int len, err;
> > 
> >  	len = calc_evm_hash(file, hash);
> > @@ -519,7 +519,7 @@ static int sign_evm(const char *file, const char *key)
> >  		return len;
> > 
> >  	len = sign_hash(params.hash_algo, hash, len, key, NULL, sig + 1);
> > -	assert(len < sizeof(sig));
> > +	assert(len <= MAX_SIGNATURE_SIZE);
> >  	if (len <= 1)
> >  		return len;
> > 
> 
> A similar problem occurs in sign_ima.  Without these changes
> sign_hash() succeeds, returning a length of 520 for
> sha256/streebog256. 

I will add it. Also, I found more similar errors and will fix them together.

> With these patches, for streebog256
> EVP_PKEY_CTX_set_signature_md is failing, returning -1,
> but works for sha256.

Probably your openssl does not support streebog256.

> With a similar change as this patch, it also works, returning
> 520.

This is above level than this change so it can not be related.

When I try streebog256 with similar change to sign_ima() I get error
like this:

  $ evmctl ima_sign --key privkey_rsa.pem -a streebog256 --xattr-user test.txt
  sign_hash_v2: signing failed: (invalid digest)
  error:0408C09D:rsa routines:check_padding_md:invalid digest

Which is correct.

Thanks,