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From:   David Howells <dhowells@redhat.com>
In-Reply-To: <20210312171232.2681989-4-mic@digikod.net>
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Cc:     dhowells@redhat.com, David Woodhouse <dwmw2@infradead.org>,
        Jarkko Sakkinen <jarkko@kernel.org>,
        "David S . Miller" <davem@davemloft.net>,
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        <mic@linux.microsoft.com>, Mimi Zohar <zohar@linux.ibm.com>,
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        linux-security-module@vger.kernel.org
Subject: Re: [PATCH v7 3/5] certs: Make blacklist_vet_description() more strict
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Date:   Wed, 20 Apr 2022 11:29:08 +0100
Message-ID: <648218.1650450548@warthog.procyon.org.uk>
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Micka=C3=ABl Sala=C3=BCn <mic@digikod.net> wrote:

> +	/* The following algorithm only works if prefix lengths match. */
> +	BUILD_BUG_ON(sizeof(tbs_prefix) !=3D sizeof(bin_prefix));
> +	prefix_len =3D sizeof(tbs_prefix) - 1;
> +	for (i =3D 0; *desc; desc++, i++) {
> +		if (*desc =3D=3D ':') {
> +			if (tbs_step =3D=3D prefix_len)
> +				goto found_colon;
> +			if (bin_step =3D=3D prefix_len)
> +				goto found_colon;
> +			return -EINVAL;
> +		}
> +		if (i >=3D prefix_len)
> +			return -EINVAL;
> +		if (*desc =3D=3D tbs_prefix[i])
> +			tbs_step++;
> +		if (*desc =3D=3D bin_prefix[i])
> +			bin_step++;
> +	}

I wonder if:

	static const char tbs_prefix[] =3D "tbs:";
	static const char bin_prefix[] =3D "bin:";

	if (strncmp(desc, tbs_prefix, sizeof(tbs_prefix) - 1) =3D=3D 0 ||
	    strncmp(desc, bin_prefix, sizeof(bin_prefix) - 1) =3D=3D 0)
		goto found_colon;

might be better.

David