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

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Date:   Mon, 21 Feb 2022 15:22:50 +0300
From:   Dan Carpenter <dan.carpenter@...cle.com>
To:     Michael Straube <straube.linux@...il.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 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.

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.

regards,
dan carpenter