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

Mimi Zohar
2023-11-22T14:14:34Z

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