linux-kernel - Re: [PATCH v3] exfat: integrates dir-entry getting and validation

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Date:   Wed, 26 Aug 2020 15:07:25 +0900
From:   Tetsuhiro Kohada <kohada.t2@...il.com>
To:     Namjae Jeon <namjae.jeon@...sung.com>
Cc:     kohada.tetsuhiro@...mitsubishielectric.co.jp,
        mori.takahiro@...mitsubishielectric.co.jp,
        motai.hirotaka@...mitsubishielectric.co.jp,
        'Sungjong Seo' <sj1557.seo@...sung.com>,
        linux-fsdevel@...r.kernel.org, linux-kernel@...r.kernel.org
Subject: Re: [PATCH v3] exfat: integrates dir-entry getting and validation

Thank you for quick reply!

On 2020/08/26 13:19, Namjae Jeon wrote:
>> On 2020/08/26 10:03, Namjae Jeon wrote:
>>>> Second: Range validation and type validation should not be separated.
>>>> When I started making this patch, I intended to add only range validation.
>>>> However, after the caller gets the ep, the type validation follows.
>>>> Get ep, null check of ep (= range verification), type verification is a series of procedures.
>>>> There would be no reason to keep them independent anymore.
>>>> Range and type validation is enforced when the caller uses ep.
>>> You can add a validate flags as argument of exfat_get_dentry_set(), e.g. none, basic and strict.
>>> none : only range validation.
>>> basic : range + type validation.
>>> strict : range + type + checksum and name length, etc.
>>
>> Currently, various types of verification will not be needed.
>> Let's add it when we need it.
>>>
>>>>> -	/* validiate cached dentries */
>>>>> -	for (i = 1; i < num_entries; i++) {
>>>>> -		ep = exfat_get_dentry_cached(es, i);
>>>>> -		if (!exfat_validate_entry(exfat_get_entry_type(ep), &mode))
>>>>> +	ep = exfat_get_dentry_cached(es, ENTRY_STREAM);
>>>>> +	if (!ep || ep->type != EXFAT_STREAM)
>>>>> +		goto free_es;
>>>>> +	es->de[ENTRY_STREAM] = ep;
>>>>
>>>> The value contained in stream-ext dir-entry should not be used before validating the EntrySet
>> checksum.
>>>> So I would insert EntrySet checksum validation here.
>>>> In that case, the checksum verification loop would be followed by the
>>>> TYPE_NAME verification loop, can you acceptable?
>>> Yes. That would be great.
>>
>> OK.
>> I'll add TYPE_NAME verification after checksum verification, in next patch.
>> However, I think it is enough to validate TYPE_NAME when extracting name.
>> Could you please tell me why you think you need TYPE_NAME validation here?
> I've told you on previous mail. This function should return validated dentry set after checking
> file->stream->name in sequence.

Yes. I understand that the current implementation checks in that order.
Sorry, my question was unclear.
Why do you think you should leave the TYPE_NAME validation in this function?
What kind of problem are you worried about if this function does not validate TYPE_NAME?
(for preserve the current behavior?)

Don't worry, I will add TYPE_NAME verification to the v4 patch.
I will post it later today.

BR
---
Tetsuhiro Kohada <kohada.t2@...il.com>