Re: [ima-evm-utils PATCH 09/12] Use a local hash algorithm variable when verifying file signatures

[Mimi Zohar <zohar@linux.ibm.com>]

On Wed, 2023-11-22 at 08:37 -0500, Stefan Berger wrote:
> 
> On 11/19/23 11:50, Mimi Zohar wrote:
> > Instead of relying on the "imaevm_params.algo" global variable, which
> > is not concurrency-safe, define and use a local variable.
> > 
> > Update static verify_hash_v2(), verify_hash_v3(), and verify_hash_common()
> > function definitions to include a hash algorithm argument.
> > 
> > Similarly update ima_verify_signature2() and ima_calc_hash2() to define
> > and use a local hash algorithm variable.
> > 
> > Signed-off-by: Mimi Zohar <zohar@linux.ibm.com>
> > ---
> >   src/libimaevm.c | 40 ++++++++++++++++++++++++----------------
> >   1 file changed, 24 insertions(+), 16 deletions(-)
> > 
> > diff --git a/src/libimaevm.c b/src/libimaevm.c
> > index 4c9da7a2f06b..18b6a6f27237 100644
> > --- a/src/libimaevm.c
> > +++ b/src/libimaevm.c
> > @@ -488,6 +488,7 @@ void init_public_keys(const char *keyfiles)
> >    * (Note: signature_v2_hdr struct does not contain the 'type'.)
> >    */
> >   static int verify_hash_common(void *public_keys, const char *file,
> > +			      const char *hash_algo,
> >   			      const unsigned char *hash,
> >   			      int size, unsigned char *sig, int siglen)
> >   {
> > @@ -499,7 +500,7 @@ static int verify_hash_common(void *public_keys, const char *file,
> >   	const char *st;
> >   
> >   	if (imaevm_params.verbose > LOG_INFO) {
> > -		log_info("hash(%s): ", imaevm_params.hash_algo);
> > +		log_info("hash(%s): ", hash_algo);
> >   		log_dump(hash, size);
> >   	}
> >   
> > @@ -530,7 +531,7 @@ static int verify_hash_common(void *public_keys, const char *file,
> >   	if (!EVP_PKEY_verify_init(ctx))
> >   		goto err;
> >   	st = "EVP_get_digestbyname";
> > -	if (!(md = EVP_get_digestbyname(imaevm_params.hash_algo)))
> > +	if (!(md = EVP_get_digestbyname(hash_algo)))
> >   		goto err;
> >   	st = "EVP_PKEY_CTX_set_signature_md";
> >   	if (!EVP_PKEY_CTX_set_signature_md(ctx, md))
> > @@ -566,11 +567,12 @@ err:
> >    * Return: 0 verification good, 1 verification bad, -1 error.
> >    */
> >   static int verify_hash_v2(void *public_keys, const char *file,
> > +			  const char *hash_algo,
> >   			  const unsigned char *hash,
> >   			  int size, unsigned char *sig, int siglen)
> >   {
> >   	/* note: signature_v2_hdr does not contain 'type', use sig + 1 */
> > -	return verify_hash_common(public_keys, file, hash, size,
> > +	return verify_hash_common(public_keys, file, hash_algo, hash, size,
> >   				  sig + 1, siglen - 1);
> >   }
> >   
> > @@ -581,19 +583,20 @@ static int verify_hash_v2(void *public_keys, const char *file,
> >    * Return: 0 verification good, 1 verification bad, -1 error.
> >    */
> >   static int verify_hash_v3(void *public_keys, const char *file,
> > +			  const char *hash_algo,
> >   			  const unsigned char *hash,
> >   			  int size, unsigned char *sig, int siglen)
> >   {
> >   	unsigned char sigv3_hash[MAX_DIGEST_SIZE];
> >   	int ret;
> >   
> > -	ret = calc_hash_sigv3(sig[0], NULL, hash, sigv3_hash);
> > +	ret = calc_hash_sigv3(sig[0], hash_algo, hash, sigv3_hash);
> >   	if (ret < 0)
> >   		return ret;
> >   
> >   	/* note: signature_v2_hdr does not contain 'type', use sig + 1 */
> > -	return verify_hash_common(public_keys, file, sigv3_hash, size,
> > -				  sig + 1, siglen - 1);
> > +	return verify_hash_common(public_keys, file, hash_algo, sigv3_hash,
> > +				  size, sig + 1, siglen - 1);
> >   }
> >   
> >   #define HASH_MAX_DIGESTSIZE 64	/* kernel HASH_MAX_DIGESTSIZE is 64 bytes */
> > @@ -636,8 +639,10 @@ int calc_hash_sigv3(enum evm_ima_xattr_type type, const char *algo,
> >   		return -EINVAL;
> >   	}
> >   
> > -	if (!algo)
> > -		algo = imaevm_params.hash_algo;
> > +	if (!algo) {
> > +		log_err("Hash algorithm unspecified\n");
> > +		return -EINVAL;
> > +	}
> >   
> >   	if ((hash_algo = imaevm_get_hash_algo(algo)) < 0) {
> >   		log_err("Hash algorithm %s not supported\n", algo);
> > @@ -757,10 +762,10 @@ int verify_hash2(void *public_keys, const char *file, const char *hash_algo,
> >   		return -1;
> >   #endif
> >   	} else if (sig[1] == DIGSIG_VERSION_2) {
> > -		return verify_hash_v2(public_keys, file, hash, size,
> > +		return verify_hash_v2(public_keys, file, hash_algo, hash, size,
> >   				      sig, siglen);
> >   	} else if (sig[1] == DIGSIG_VERSION_3) {
> > -		return verify_hash_v3(public_keys, file, hash, size,
> > +		return verify_hash_v3(public_keys, file, hash_algo, hash, size,
> >   				      sig, siglen);
> >   	} else
> >   		return -1;
> > @@ -774,7 +779,8 @@ int verify_hash2(void *public_keys, const char *file, const char *hash_algo,
> >   int verify_hash(const char *file, const unsigned char *hash, int size,
> >   		unsigned char *sig, int siglen)
> >   {
> > -	return verify_hash2(g_public_keys, file, NULL, hash, size, sig, siglen);
> > +	return verify_hash2(g_public_keys, file, imaevm_params.hash_algo,
> > +			    hash, size, sig, siglen);
> 
> Now you are passing valid parameters into verify_hash2(). Would it not 
> be possible to drop 4/12?

Just as we can't modify the library verify_hash() definition, I don't
think we should be modifying the verify_hash2() defintion either. 
04/12 defines and exports the final verify_hash2() definition.

-- 
thanks,

Mimi