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

From: Mimi Zohar <zohar@linux.ibm.com>
To: Vitaly Chikunov <vt@altlinux.org>
Cc: Mimi Zohar <zohar@linux.vnet.ibm.com>,
	Dmitry Kasatkin <dmitry.kasatkin@gmail.com>,
	linux-integrity@vger.kernel.org
Subject: Re: [PATCH v3 7/7] ima-evm-utils: Try to load digest by its alias
Date: Mon, 11 Feb 2019 15:21:03 -0500	[thread overview]
Message-ID: <1549916463.12743.188.camel@linux.ibm.com> (raw)
In-Reply-To: <20190211192644.q7ipos4rrmj7vugq@altlinux.org>

On Mon, 2019-02-11 at 22:26 +0300, Vitaly Chikunov wrote:
> Mimi,
> 
> On Mon, Feb 11, 2019 at 09:21:15PM +0300, Vitaly Chikunov wrote:
> > On Mon, Feb 11, 2019 at 09:13:00PM +0300, Vitaly Chikunov wrote:
> > > 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.
> 
> Or you may suggest simpler approach.
> 
> Basically, we need to resole both text strings into the same PKEY_HASH_
> id, allow any of the string pass into EVP_get_digestbyname, and resolve
> PKEY_HASH_ id back into the correct hash name. Optionally, allow user to
> specify new hash name on older openssl/gost-engine. This is all
> implemented by that patch, it was not just overly complicated "hash
> algorithm comparison".
> 
> My wish is we retain support of older openssl/gost-engine.

The following seems to fix the problem, but instead of adding it in
strmatch(), as below, I would add it before the strmatch() call.  Then
strmatch is only called as needed.

diff --git a/src/libimaevm.c b/src/libimaevm.c
index d9ffa13befb0..7901215da655 100644
--- a/src/libimaevm.c
+++ b/src/libimaevm.c
@@ -598,6 +598,9 @@ static int strmatch(const char *needle, const char *haystack)
        const char *p = haystack;
        const char *t;
 
+       if (strcmp(needle, haystack) == 0)
+               return 0;
+
        for (t = strchrnul(p, ','); *p; p = t, t = strchrnul(p, ',')) {
                if (t - p == len &&
                    !strncmp(needle, p, len))

Mimi

