Re: [PATCH] wifi: brcmfmac: Adjust n_channels usage for __counted_by

["Gustavo A. R. Silva" <gustavo@embeddedor.com>]

On 1/26/24 16:31, Kees Cook wrote:
> After commit e3eac9f32ec0 ("wifi: cfg80211: Annotate struct
> cfg80211_scan_request with __counted_by"), the compiler may enforce
> dynamic array indexing of req->channels to stay below n_channels. As a
> result, n_channels needs to be increased _before_ accessing the newly
> added array index. Increment it first, then use "i" for the prior index.
> Solves this warning in the coming GCC that has __counted_by support:
> 
> ../drivers/net/wireless/broadcom/brcm80211/brcmfmac/cfg80211.c: In function 'brcmf_internal_escan_add_info':
> ../drivers/net/wireless/broadcom/brcm80211/brcmfmac/cfg80211.c:3783:46: warning: operation on 'req->
> n_channels' may be undefined [-Wsequence-point]
>   3783 |                 req->channels[req->n_channels++] = chan;
>        |                               ~~~~~~~~~~~~~~~^~
> 
> Fixes: e3eac9f32ec0 ("wifi: cfg80211: Annotate struct cfg80211_scan_request with __counted_by")
> Cc: Arend van Spriel <aspriel@gmail.com>
> Cc: Franky Lin <franky.lin@broadcom.com>
> Cc: Hante Meuleman <hante.meuleman@broadcom.com>
> Cc: Kalle Valo <kvalo@kernel.org>
> Cc: Chi-hsien Lin <chi-hsien.lin@infineon.com>
> Cc: Ian Lin <ian.lin@infineon.com>
> Cc: Johannes Berg <johannes.berg@intel.com>
> Cc: Wright Feng <wright.feng@cypress.com>
> Cc: Hector Martin <marcan@marcan.st>
> Cc: linux-wireless@vger.kernel.org
> Cc: brcm80211-dev-list.pdl@broadcom.com
> Signed-off-by: Kees Cook <keescook@chromium.org>

Reviewed-by: Gustavo A. R. Silva <gustavoars@kernel.org>

Thanks!
-- 
Gustavo

> ---
>   drivers/net/wireless/broadcom/brcm80211/brcmfmac/cfg80211.c | 6 ++++--
>   1 file changed, 4 insertions(+), 2 deletions(-)
> 
> diff --git a/drivers/net/wireless/broadcom/brcm80211/brcmfmac/cfg80211.c b/drivers/net/wireless/broadcom/brcm80211/brcmfmac/cfg80211.c
> index 133c5ea6429c..28d6a30cc010 100644
> --- a/drivers/net/wireless/broadcom/brcm80211/brcmfmac/cfg80211.c
> +++ b/drivers/net/wireless/broadcom/brcm80211/brcmfmac/cfg80211.c
> @@ -3779,8 +3779,10 @@ static int brcmf_internal_escan_add_info(struct cfg80211_scan_request *req,
>   		if (req->channels[i] == chan)
>   			break;
>   	}
> -	if (i == req->n_channels)
> -		req->channels[req->n_channels++] = chan;
> +	if (i == req->n_channels) {
> +		req->n_channels++;
> +		req->channels[i] = chan;
> +	}
>   
>   	for (i = 0; i < req->n_ssids; i++) {
>   		if (req->ssids[i].ssid_len == ssid_len &&