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

[Kees Cook]

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@xxxxxxxxx>
Cc: Franky Lin <franky.lin@xxxxxxxxxxxx>
Cc: Hante Meuleman <hante.meuleman@xxxxxxxxxxxx>
Cc: Kalle Valo <kvalo@xxxxxxxxxx>
Cc: Chi-hsien Lin <chi-hsien.lin@xxxxxxxxxxxx>
Cc: Ian Lin <ian.lin@xxxxxxxxxxxx>
Cc: Johannes Berg <johannes.berg@xxxxxxxxx>
Cc: Wright Feng <wright.feng@xxxxxxxxxxx>
Cc: Hector Martin <marcan@xxxxxxxxx>
Cc: linux-wireless@xxxxxxxxxxxxxxx
Cc: brcm80211-dev-list.pdl@xxxxxxxxxxxx
Signed-off-by: Kees Cook <keescook@xxxxxxxxxxxx>
---
 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 &&
-- 
2.34.1