[PATCH wireless-next v2] net: cfg80211: validate monitor channel set against radio usage

[Rory Little <roryl@candelatech.com>]

Current logic only looks globally at interface counts to validate that a
monitor can have its channel configured. This works to ensure that the
wiphy is not pulled off the channel currently being used by another
active interface, but fails to allow for the case where the channels in
use on the other active interface and the desired channel for the
monitor fall on disjoint sets of radios.

Instead, search for any interface which would cause conflict, otherwise
allowing for the configuration.

Suggested-by: Dylan Eskew <dylan.eskew@candelatech.com>
Signed-off-by: Rory Little <roryl@candelatech.com>
---
v2:
- Handle error return from cfg80211_get_radio_idx_by_chan
- Fixed subject line

 net/wireless/chan.c | 29 ++++++++++++++++++++++++++++-
 1 file changed, 28 insertions(+), 1 deletion(-)

diff --git a/net/wireless/chan.c b/net/wireless/chan.c
index 1071e823108b..679f1152ba65 100644
--- a/net/wireless/chan.c
+++ b/net/wireless/chan.c
@@ -1810,13 +1810,40 @@ bool cfg80211_reg_check_beaconing(struct wiphy *wiphy,
 }
 EXPORT_SYMBOL(cfg80211_reg_check_beaconing);
 
+static bool cfg80211_can_set_monitor_channel(struct cfg80211_registered_device *rdev,
+					     struct cfg80211_chan_def *chandef)
+{
+	struct wireless_dev *wdev;
+	int radio_idx;
+
+	lockdep_assert_held(&rdev->wiphy.mtx);
+
+	if (cfg80211_has_monitors_only(rdev))
+		return true;
+
+	radio_idx = cfg80211_get_radio_idx_by_chan(&rdev->wiphy, chandef->chan);
+	if (radio_idx < 0)
+		return false;
+
+	list_for_each_entry(wdev, &rdev->wiphy.wdev_list, list) {
+		if (wdev->iftype == NL80211_IFTYPE_MONITOR)
+			continue;
+		if (!wdev->netdev)
+			continue;
+		if (rdev_get_radio_mask(rdev, wdev->netdev) & BIT(radio_idx))
+			return false;
+	}
+
+	return true;
+}
+
 int cfg80211_set_monitor_channel(struct cfg80211_registered_device *rdev,
 				 struct net_device *dev,
 				 struct cfg80211_chan_def *chandef)
 {
 	if (!rdev->ops->set_monitor_channel)
 		return -EOPNOTSUPP;
-	if (!cfg80211_has_monitors_only(rdev))
+	if (!cfg80211_can_set_monitor_channel(rdev, chandef))
 		return -EBUSY;
 
 	return rdev_set_monitor_channel(rdev, dev, chandef);
-- 
2.52.0