[PATCH 5.2 026/124] nl80211: Fix possible Spectre-v1 for CQM RSSI thresholds

[Greg Kroah-Hartman]

From: Masashi Honma <masashi.honma@xxxxxxxxx>

commit 4b2c5a14cd8005a900075f7dfec87473c6ee66fb upstream.

commit 1222a1601488 ("nl80211: Fix possible Spectre-v1 for CQM
RSSI thresholds") was incomplete and requires one more fix to
prevent accessing to rssi_thresholds[n] because user can control
rssi_thresholds[i] values to make i reach to n. For example,
rssi_thresholds = {-400, -300, -200, -100} when last is -34.

Cc: stable@xxxxxxxxxxxxxxx
Fixes: 1222a1601488 ("nl80211: Fix possible Spectre-v1 for CQM RSSI thresholds")
Reported-by: Dan Carpenter <dan.carpenter@xxxxxxxxxx>
Signed-off-by: Masashi Honma <masashi.honma@xxxxxxxxx>
Link: https://lore.kernel.org/r/20190908005653.17433-1-masashi.honma@xxxxxxxxx
Signed-off-by: Johannes Berg <johannes.berg@xxxxxxxxx>
Signed-off-by: Greg Kroah-Hartman <gregkh@xxxxxxxxxxxxxxxxxxx>

---
 net/wireless/nl80211.c |    4 +++-
 1 file changed, 3 insertions(+), 1 deletion(-)

--- a/net/wireless/nl80211.c
+++ b/net/wireless/nl80211.c
@@ -10640,9 +10640,11 @@ static int cfg80211_cqm_rssi_update(stru
 	hyst = wdev->cqm_config->rssi_hyst;
 	n = wdev->cqm_config->n_rssi_thresholds;
 
-	for (i = 0; i < n; i++)
+	for (i = 0; i < n; i++) {
+		i = array_index_nospec(i, n);
 		if (last < wdev->cqm_config->rssi_thresholds[i])
 			break;
+	}
 
 	low_index = i - 1;
 	if (low_index >= 0) {