Re: [PATCH 2/3] staging: r8188eu: refactor rtw_ch2freq()

[Michael Straube]

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