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

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Date:   Thu, 21 Apr 2022 19:29:10 +0200
From:   Mickaël Salaün <mic@...ikod.net>
To:     Jarkko Sakkinen <jarkko@...nel.org>
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 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.