linux-kernel - wifi: mac80211: make n_channels updated absolutely before accessing channels[]

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Message-ID: <20251112163750463kAkOIyBxvHkYWh9Cgdypb@zte.com.cn>
Date: Wed, 12 Nov 2025 16:37:50 +0800 (CST)
From: <xu.xin16@....com.cn>
To: <johannes@...solutions.net>
Cc: <kees@...nel.org>, <concord@...too.org>, <linux-wireless@...r.kernel.org>,
        <linux-kernel@...r.kernel.org>, <qiu.yutan@....com.cn>
Subject: wifi: mac80211: make n_channels updated absolutely before accessing channels[]

From: xu xin <xu.xin16@....com.cn>

The commit 2663d0462eb3 ("wifi: mac80211: Avoid address calculations via out of
bounds array indexing") said that req->n_channels must be set before
req->channels[] can be used. But there&apos;s still the case that req.channels
accessing was prior to n_channels++.

This does not fix any visible bug, just making n_channels updated before
accessing channels[] absolutely, to avoid potential UBSAN out of indexing
warning.

Fixes: 2663d0462eb3 ("wifi: mac80211: Avoid address calculations via out of bounds array indexing")
Signed-off-by: xu xin <xu.xin16@....com.cn>
---
net/mac80211/scan.c | 4 +++-
1 file changed, 3 insertions(+), 1 deletion(-)

diff --git a/net/mac80211/scan.c b/net/mac80211/scan.c
index 5ef315ed3b0f..86bd85ac36be 100644
--- a/net/mac80211/scan.c
+++ b/net/mac80211/scan.c
@@ -406,7 +406,9 @@ static bool ieee80211_prep_hw_scan(struct ieee80211_sub_if_data *sdata)
 				if (req->channels[i]->band !=
 				local->hw_scan_band)
 					continue;
-				local->hw_scan_req->req.channels[(*n_chans)++] =
+				(*n_chans)++;
+				/* Use *n_chans - 1 to access the index that was valid before incrementing */
+				local->hw_scan_req->req.channels[*n_chans - 1] =
 							req->channels[i];

 				bands_used |= BIT(req->channels[i]->band);
--
2.25.1