linux-kernel - Re: [PATCH 2/3] staging: r8188eu: refactor rtw

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Date:   Mon, 21 Feb 2022 20:20:14 +0100
From:   Michael Straube <straube.linux@...il.com>
To:     Dan Carpenter <dan.carpenter@...cle.com>
Cc:     Pavel Skripkin <paskripkin@...il.com>, gregkh@...uxfoundation.org,
        Larry.Finger@...inger.net, phil@...lpotter.co.uk,
        linux-staging@...ts.linux.dev, linux-kernel@...r.kernel.org
Subject: Re: [PATCH 2/3] staging: r8188eu: refactor rtw_ch2freq()

On 2/21/22 13:22, Dan Carpenter wrote:
> On Sun, Feb 20, 2022 at 05:30:08PM +0100, Michael Straube wrote:
>> On 2/20/22 17:20, Pavel Skripkin wrote:
>>> Hi Michael,
>>>
>>> On 2/20/22 18:48, Michael Straube wrote:
>>>> -static int ch_freq_map_num = ARRAY_SIZE(ch_freq_map);
>>>> -
>>>>    u32 rtw_ch2freq(u32 channel)
>>>>    {
>>>> -    u8    i;
>>>> -    u32    freq = 0;
>>>> -
>>>> -    for (i = 0; i < ch_freq_map_num; i++) {
>>>> -        if (channel == ch_freq_map[i].channel) {
>>>> -            freq = ch_freq_map[i].frequency;
>>>> -                break;
>>>> -        }
>>>> -    }
>>>> -    if (i == ch_freq_map_num)
>>>> -        freq = 2412;
>>>> -
>>>> -    return freq;
>>>> +    return ch_freq_map[channel - 1];
>>>>    }
>>>
>>> What if channel has wrong value? The old code returned some default
>>> value, but with new one we will hit OOB.
>>>
>>
>> Hi Pavel,
>>
>> thanks for reviewing. Yeah, I thought about adding a check for channel
>> value between 1 and 14. But I did not add it because I think if this
>> function will ever be called with channel < 1 or channel > 14, then the
>> calling code must be wrong.
>>
>> Would be nice to see what others think about this.
> 
> I'm glad that Pavel noticed this change.  This is a risky thing and
> should have been noted in the commit message.
> 
> Just from a review stand point it would be best to leave the original
> behavior.
>

Do you mean to leave the whole original code including the 5 GHz 
frequencies? Or returning a default value if we have a channel value < 1
or > 14?

I'm a bit confused now, because Greg asked how we know that the driver
is only for 2.4 GHz chips.

> I have audited this change and I do not think it is safe.  It seems to
> me that one way this can be controlled is via
> module_param(rtw_channel, int, 0644); in
> drivers/staging/r8188eu/os_dep/os_intfs.c.  I don't see any checking on
> that.
> 

Thank you Dan!

I missed that and blindly assumed the function will never be called
with channel values OOB. That was not good, sorry.

regards,

Michael