linux-kernel - Re: [PATCH] crypto: hisilicon/hpre - Fix a erroneous check after snprintf()

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Message-ID: <492ae2a2-3364-f13c-4d93-0175221483a9@wanadoo.fr>
Date:   Fri, 8 Sep 2023 18:11:17 +0200
From:   Christophe JAILLET <christophe.jaillet@...adoo.fr>
To:     liulongfang <liulongfang@...wei.com>,
        Herbert Xu <herbert@...dor.apana.org.au>
Cc:     "David S. Miller" <davem@...emloft.net>,
        Zaibo Xu <xuzaibo@...wei.com>, linux-kernel@...r.kernel.org,
        kernel-janitors@...r.kernel.org, linux-crypto@...r.kernel.org
Subject: Re: [PATCH] crypto: hisilicon/hpre - Fix a erroneous check after
 snprintf()

Le 06/09/2023 à 04:04, liulongfang a écrit :
> On 2023/9/5 16:17, Herbert Xu wrote:
>> On Tue, Sep 05, 2023 at 07:27:47AM +0200, Marion & Christophe JAILLET wrote:
>>>
>>> Some debugfs dir of file way be left around. Is it what your are talking
>>> about?
>>
>> Yes all allocated resources should be freed on the error path.
>>
>>>> The other snprintf in the same file also looks suspect.
>>>
>>> It looks correct to me.
>>>
>>> And HPRE_DBGFS_VAL_MAX_LEN being 20, it doesn't really matter. The string
>>> can't be truncated with just a "%u\n".
>>
>> Well if you're going to go with that line of reasoning then this
>> case ("cluster%d") can't overflow either, no?
>>
> 
> First, I checked the calling code of the snprintf function in all driver files in
> the hisilicon directory. Only here is the processing of return value judgment.
> This treatment is indeed problematic and needs to be modified.
> 
> Then, I don't quite agree with your modification plan.
> The modification of this solution is not complete.
> As Herbert said, ("cluster%d") may still have overflow problems.

Herbert said the contrary, and I agree with him.

HPRE_DBGFS_VAL_MAX_LEN is 20.

cluster%u will be at max:
	strlen("cluster") + strlen("4294967295") + 1 = 17

(unless some system have 64 bits int?)

I do agree that it is safe to remove the test after snprintf(), but 
there is no need from my POV to turn "i" into a u8.

CJ

> 
> In the end, my proposed modification scheme is this:
> ...
> 	int ret;
> 	u8 i;
> 
> 	for (i = 0; i < clusters_num; i++) {
> 		snprintf(buf, HPRE_DBGFS_VAL_MAX_LEN, "cluster%u", i);
> 		tmp_d = debugfs_create_dir(buf, qm->debug.debug_root);
> 		...
> 	}
> ...
> 
> Thanks,
> Longfang.
> 
>> Cheers,
>>
>