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

[Vitaly Chikunov <vt@altlinux.org>]

Mimi,

On Mon, Feb 11, 2019 at 12:59:12PM -0500, Mimi Zohar wrote:
> On Mon, 2019-02-11 at 20:52 +0300, Vitaly Chikunov wrote:
> > On Mon, Feb 11, 2019 at 12:38:58PM -0500, Mimi Zohar wrote:
> > > 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.
> > 
> > Yes, it's fixed in "ima-evm-utils: convert sign v2 from RSA to EVP_PKEY
> > API". I didn't consider it a problem since streebog256 should not work
> > for sign/verify anyway (since RSA should not support it). That EVP_PKEY
> > patch which adds ability to sign/verify for Streebog also fixes above
> > problem.
> 
> I've been having second thoughts about this patch in general, as it
> made the hash algorithm comparison unnecessarily more complex for the
> simple case.  As there hasn't been a new ima-evm-utils release with
> patch, perhaps we should simple remove/revert it?

It was only for compatibility with older openssl/gost-engine, where
"streebog256" name is not defined yet. If you don't want to allow that
users to use Streebog feel free to revert it.

I was not found this mistake at the time, since Streebog should only be
used in ima_hash and not in ima_sign/verify (which requires RSA support
which I intentionally didn't add, planning to add EC-RDSA support later),
so that code path was not tested.

> 
> Mimi
> 
> > 
> > > 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 */
> >