Re: [PATCH v3 7/7] ima-evm-utils: Try to load digest by its alias

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

Hi Vitaly,

On Mon, 2018-12-03 at 06:35 +0300, Vitaly Chikunov wrote:
> For compatibility with older OpenSSL try to load digest by its alias if
> load by its proper name is failed.
> 
> This is configured in pkey_hash_algo by mentioning loadable alias first in the
> comma separated list of algo names.

After this patch, I can not verify the signature.  It's failing to
find the hash algorithm.

evmctl ima_sign -k <private key> -p -a streebog256 ./foo.txt  --xattr-user
evmctl ima_verify -k <public key>  ./foo.txt  --xattr-user

Mimi

> 
> Signed-off-by: Vitaly Chikunov <vt@altlinux.org>
> ---
> Changes since v1:
> - New patch.
> Changes since v2:
> - No changes.
> 
>  src/imaevm.h    |  1 +
>  src/libimaevm.c | 55 +++++++++++++++++++++++++++++++++++++++++++++++++++----
>  2 files changed, 52 insertions(+), 4 deletions(-)
> 
> diff --git a/src/imaevm.h b/src/imaevm.h
> index c81bf21..795966a 100644
> --- a/src/imaevm.h
> +++ b/src/imaevm.h
> @@ -75,6 +75,7 @@
>  #define	DATA_SIZE	4096
>  #define SHA1_HASH_LEN   20
> 
> +#define MAX_DIGEST_NAME		32
>  #define MAX_DIGEST_SIZE		64
>  #define MAX_SIGNATURE_SIZE	1024
> 
> diff --git a/src/libimaevm.c b/src/libimaevm.c
> index cb4721b..7501303 100644
> --- a/src/libimaevm.c
> +++ b/src/libimaevm.c
> @@ -41,6 +41,7 @@
>  /* should we use logger instead for library? */
>  #define USE_FPRINTF
> 
> +#define _GNU_SOURCE
>  #include <sys/types.h>
>  #include <sys/param.h>
>  #include <sys/stat.h>
> @@ -56,6 +57,7 @@
>  #include <openssl/pem.h>
>  #include <openssl/evp.h>
>  #include <openssl/x509.h>
> +#include <openssl/engine.h>
>  #include <openssl/err.h>
> 
>  #include "imaevm.h"
> @@ -70,8 +72,8 @@ const char *const pkey_hash_algo[PKEY_HASH__LAST] = {
>  	[PKEY_HASH_SHA384]	= "sha384",
>  	[PKEY_HASH_SHA512]	= "sha512",
>  	[PKEY_HASH_SHA224]	= "sha224",
> -	[PKEY_HASH_STREEBOG_256] = "streebog256",
> -	[PKEY_HASH_STREEBOG_512] = "streebog512",
> +	[PKEY_HASH_STREEBOG_256] = "md_gost12_256,streebog256",
> +	[PKEY_HASH_STREEBOG_512] = "md_gost12_512,streebog512",
>  };
> 
>  /*
> @@ -284,6 +286,35 @@ static int add_dev_hash(struct stat *st, EVP_MD_CTX *ctx)
>  	return !EVP_DigestUpdate(ctx, &dev, sizeof(dev));
>  }
> 
> +/* Call EVP_get_digestbyname with provided name and with alias,
> + * which is first name in the comma separated list of names
> + * in pkey_hash_algo.
> + */
> +static const EVP_MD *get_digestbyname(const char *name)
> +{
> +	const EVP_MD *md;
> +
> +	md = EVP_get_digestbyname(params.hash_algo);
> +	if (!md) {
> +		char alias[MAX_DIGEST_NAME];
> +		int len;
> +		int algo_id;
> +		const char *algo_alias;
> +
> +		/* try to get algo by its alias */
> +		algo_id = get_hash_algo(params.hash_algo);
> +		algo_alias = get_hash_algo_by_id(algo_id);
> +		len = strchrnul(algo_alias, ',') - algo_alias;
> +		if (len < sizeof(alias)) {
> +			memcpy(alias, algo_alias, len);
> +			alias[len] = '\0';
> +			if (strcmp(params.hash_algo, alias))
> +				md = EVP_get_digestbyname(alias);
> +		}
> +	}
> +	return md;
> +}
> +
>  int ima_calc_hash(const char *file, uint8_t *hash)
>  {
>  	const EVP_MD *md;
> @@ -305,7 +336,7 @@ int ima_calc_hash(const char *file, uint8_t *hash)
>  		return err;
>  	}
> 
> -	md = EVP_get_digestbyname(params.hash_algo);
> +	md = get_digestbyname(params.hash_algo);
>  	if (!md) {
>  		log_err("EVP_get_digestbyname(%s) failed\n", params.hash_algo);
>  		return 1;
> @@ -561,6 +592,22 @@ static int algocmp(const char *a, const char *b)
>  	return *a || *b;
>  }
> 
> +static int strmatch(const char *needle, const char *haystack)
> +{
> +	int len = strlen(needle);
> +	const char *p = haystack;
> +	const char *t;
> +
> +	for (t = strchrnul(p, ','); *p; p = t, t = strchrnul(p, ',')) {
> +		if (t - p == len &&
> +		    !strncmp(needle, p, len))
> +			return 0;
> +		if (!*t++)
> +			break;
> +	}
> +	return 1;
> +}
> +
>  int get_hash_algo(const char *algo)
>  {
>  	int i;
> @@ -568,7 +615,7 @@ int get_hash_algo(const char *algo)
>  	/* first iterate over builtin algorithms */
>  	for (i = 0; i < PKEY_HASH__LAST; i++)
>  		if (pkey_hash_algo[i] &&
> -		    !strcmp(algo, pkey_hash_algo[i]))
> +		    !strmatch(algo, pkey_hash_algo[i]))
>  			return i;
> 
>  	/* iterate over algorithms provided by kernel-headers */