# Re: \[PATCH 1/2\] b43legacy: fix a lower bounds test

- From: Michael Büsch \<m@bues.ch\>
- Date: 2021-10-06 16:55:41 
- List: linux-wireless
- Page: https://ratatoskr.run/linux-wireless/2021/10/13158276
- Thread: https://ratatoskr.run/linux-wireless/2021/10/13158273/t.md

```text
On Wed, 6 Oct 2021 10:35:42 +0300
Dan Carpenter [ref] wrote:

> The problem is that "channel" is an unsigned int, when it's less 5 the
> value of "channel - 5" is not a negative number as one would expect but
> is very high positive value instead.
> 
> This means that "start" becomes a very high positive value.  The result
> of that is that we never enter the "for (i = start; i <= end; i++) {"
> loop.  Instead of storing the result from b43legacy_radio_aci_detect()
> it just uses zero.
> 
> Fixes: 75388acd0cd8 ("[B43LEGACY]: add mac80211-based driver for legacy BCM43xx devices")
> Signed-off-by: Dan Carpenter <redacted>
> ---
> This fix is correct, but making dead code go live can sometimes expose
> bugs which were previously hiding and is always carries a slight risk.
> 
>  drivers/net/wireless/broadcom/b43legacy/radio.c | 2 +-
>  1 file changed, 1 insertion(+), 1 deletion(-)
> 
> diff --git a/drivers/net/wireless/broadcom/b43legacy/radio.c b/drivers/net/wireless/broadcom/b43legacy/radio.c
> index 06891b4f837b..fdf78c10a05c 100644
> --- a/drivers/net/wireless/broadcom/b43legacy/radio.c
> +++ b/drivers/net/wireless/broadcom/b43legacy/radio.c
> @@ -283,7 +283,7 @@ u8 b43legacy_radio_aci_scan(struct b43legacy_wldev *dev)
>  			    & 0x7FFF);
>  	b43legacy_set_all_gains(dev, 3, 8, 1);
>  
> -	start = (channel - 5 > 0) ? channel - 5 : 1;
> +	start = (channel > 5) ? channel - 5 : 1;
>  	end = (channel + 5 < 14) ? channel + 5 : 13;
>  
>  	for (i = start; i <= end; i++) {

Nice finding.

Acked-by: Michael Büsch <m@bues.ch>


-- 
Michael

https://bues.ch/
```

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