linux-kernel - Re: [PATCH 3/7] mtd: spi-nor: add restriction for nmaps in smpt parser

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Message-ID: <e6e7b441-9dff-1265-4820-e29ad2ae0e0b@microchip.com>
Date:   Thu, 8 Nov 2018 15:00:34 +0000
From:   <Tudor.Ambarus@...rochip.com>
To:     <boris.brezillon@...tlin.com>
CC:     <marek.vasut@...il.com>, <dwmw2@...radead.org>,
        <computersforpeace@...il.com>, <richard@....at>,
        <linux-mtd@...ts.infradead.org>, <linux-kernel@...r.kernel.org>,
        <yogeshnarayan.gaur@....com>, <cyrille.pitchen@...ev4u.fr>
Subject: Re: [PATCH 3/7] mtd: spi-nor: add restriction for nmaps in smpt
 parser



On 11/08/2018 04:54 PM, Boris Brezillon wrote:
> On Thu, 8 Nov 2018 14:48:11 +0000
> <Tudor.Ambarus@...rochip.com> wrote:
>   
>>>>>> +    
>>>>>
>>>>> Maybe I missed something but it sounds like this change is just
>>>>> optimizing the SPMT parsing a bit, and to be honest, I'm not sure this
>>>>> is really needed. Most of the time, smpt_len will be rather small, so
>>>>> trying to bail out earlier is not bringing much perf improvements.    
>>>>
>>>> It's rather a smtp validity check. I want to return an error if there are not
>>>> enough detection commands to identify the map id.  
>>>
>>> You would have failed the same way without this validity check after a
>>> maximum of smpt_len iterations, right?
>>>   
>>
>> Right. The correct fix would be to count nmaps in a loop, then do these checks,
>> and if all ok, search for the map_id in another loop :).
> 
> Or just error out when !ncmds && nmaps > 1.

Solves partially the problem.

> 
> If you insist on keeping the ncmds && nmaps >= (1 << (ncmds + 1))
> check, that's fine, but it's not replacing the consistency check I was
> doing ;-).
> 

I don't have a strong opinion on this, we can live without these checks as well.