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

Stefan Berger
2023-11-22T13:37:11Z

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?