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

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Message-ID: <YmJtT/lOmxEwPMDD@kernel.org>
Date:   Fri, 22 Apr 2022 11:54:39 +0300
From:   Jarkko Sakkinen <jarkko@...nel.org>
To:     Mickaël Salaün <mic@...ikod.net>
Cc:     David Howells <dhowells@...hat.com>,
        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>,
        Mickaël Salaün <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 Thu, Apr 21, 2022 at 07:29:10PM +0200, Mickaël Salaün wrote:
> 
> On 21/04/2022 17:57, Jarkko Sakkinen wrote:
> > On Thu, Apr 21, 2022 at 05:27:42PM +0200, Mickaël Salaün wrote:
> > > 
> > > On 21/04/2022 17:12, Jarkko Sakkinen wrote:
> > > > 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
> > > 
> > > I'm confused. Didn't you plan to send this patch series before v5.18-rc2?
> > > It's been a while since I started working on this.
> > 
> > That was my original plan but due to some other things, I've sent
> > a PR for rc4. I CC'd you to the PR.
> 
> OK, I missed it. My micro-optimization isn't worth it, strncmp is much
> simple indeed.

Yeah, anyway, it's fine to submit this as a separate cleanup.

It's anyway working and tested code.

BR, Jarkko