linux-kernel - Re: [PATCH v7 3/5] certs: Make blacklist_vet

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Message-ID: <YmF0eAh7dYmtLDVx@kernel.org>
Date:   Thu, 21 Apr 2022 18:12:56 +0300
From:   Jarkko Sakkinen <jarkko@...nel.org>
To:     David Howells <dhowells@...hat.com>
Cc:     =?UTF-8?q?Micka=C3=ABl=20Sala=C3=BCn?= 
        <mic@...ikod.net>, David Woodhouse <dwmw2@...radead.org>,
        "David S . Miller" <davem@...emloft.net>,
        Eric Snowberg <eric.snowberg@...cle.com>,
        Herbert Xu <herbert@...dor.apana.org.au>,
        James Morris <jmorris@...ei.org>,
        =?UTF-8?q?Micka=C3=ABl=20Sala=C3=BCn?= 
        <mic@...ux.microsoft.com>, Mimi Zohar <zohar@...ux.ibm.com>,
        "Serge E . Hallyn" <serge@...lyn.com>,
        Tyler Hicks <tyhicks@...ux.microsoft.com>,
        keyrings@...r.kernel.org, linux-crypto@...r.kernel.org,
        linux-integrity@...r.kernel.org, linux-kernel@...r.kernel.org,
        linux-security-module@...r.kernel.org
Subject: Re: [PATCH v7 3/5] certs: Make blacklist_vet_description() more
 strict

On Wed, Apr 20, 2022 at 11:29:08AM +0100, David Howells wrote:
> Mickaël Salaün <mic@...ikod.net> wrote:
> 
> > +	/* The following algorithm only works if prefix lengths match. */
> > +	BUILD_BUG_ON(sizeof(tbs_prefix) != sizeof(bin_prefix));
> > +	prefix_len = sizeof(tbs_prefix) - 1;
> > +	for (i = 0; *desc; desc++, i++) {
> > +		if (*desc == ':') {
> > +			if (tbs_step == prefix_len)
> > +				goto found_colon;
> > +			if (bin_step == prefix_len)
> > +				goto found_colon;
> > +			return -EINVAL;
> > +		}
> > +		if (i >= prefix_len)
> > +			return -EINVAL;
> > +		if (*desc == tbs_prefix[i])
> > +			tbs_step++;
> > +		if (*desc == bin_prefix[i])
> > +			bin_step++;
> > +	}
> 
> I wonder if:
> 
> 	static const char tbs_prefix[] = "tbs:";
> 	static const char bin_prefix[] = "bin:";
> 
> 	if (strncmp(desc, tbs_prefix, sizeof(tbs_prefix) - 1) == 0 ||
> 	    strncmp(desc, bin_prefix, sizeof(bin_prefix) - 1) == 0)
> 		goto found_colon;
> 
> might be better.
> 
> David

I think it'd be. 

BR, Jarkko