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

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Date:   Wed, 20 Apr 2022 11:29:08 +0100
From:   David Howells <dhowells@...hat.com>
To:     =?UTF-8?q?Micka=C3=ABl=20Sala=C3=BCn?= <mic@...ikod.net>
Cc:     dhowells@...hat.com, David Woodhouse <dwmw2@...radead.org>,
        Jarkko Sakkinen <jarkko@...nel.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

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