linux-hardening - [PATCH] wifi: brcmfmac: Adjust n_channels usage for __counted

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Date: Fri, 26 Jan 2024 14:31:53 -0800
From: Kees Cook <keescook@...omium.org>
To: Arend van Spriel <aspriel@...il.com>
Cc: Kees Cook <keescook@...omium.org>,
	Franky Lin <franky.lin@...adcom.com>,
	Hante Meuleman <hante.meuleman@...adcom.com>,
	Kalle Valo <kvalo@...nel.org>,
	Chi-hsien Lin <chi-hsien.lin@...ineon.com>,
	Ian Lin <ian.lin@...ineon.com>,
	Johannes Berg <johannes.berg@...el.com>,
	Wright Feng <wright.feng@...ress.com>,
	Hector Martin <marcan@...can.st>,
	linux-wireless@...r.kernel.org,
	brcm80211-dev-list.pdl@...adcom.com,
	"Gustavo A. R. Silva" <gustavoars@...nel.org>,
	Linus Walleij <linus.walleij@...aro.org>,
	Jisoo Jang <jisoo.jang@...sei.ac.kr>,
	Hans de Goede <hdegoede@...hat.com>,
	Aloka Dixit <quic_alokad@...cinc.com>,
	John Keeping <john@...ping.me.uk>,
	Jeff Johnson <quic_jjohnson@...cinc.com>,
	linux-kernel@...r.kernel.org,
	linux-hardening@...r.kernel.org
Subject: [PATCH] wifi: brcmfmac: Adjust n_channels usage for __counted_by

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@...il.com>
Cc: Franky Lin <franky.lin@...adcom.com>
Cc: Hante Meuleman <hante.meuleman@...adcom.com>
Cc: Kalle Valo <kvalo@...nel.org>
Cc: Chi-hsien Lin <chi-hsien.lin@...ineon.com>
Cc: Ian Lin <ian.lin@...ineon.com>
Cc: Johannes Berg <johannes.berg@...el.com>
Cc: Wright Feng <wright.feng@...ress.com>
Cc: Hector Martin <marcan@...can.st>
Cc: linux-wireless@...r.kernel.org
Cc: brcm80211-dev-list.pdl@...adcom.com
Signed-off-by: Kees Cook <keescook@...omium.org>
---
 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