wifi: cfg80211: optionally support monitor on disabled channels

If the hardware supports a disabled channel, it may in
some cases be possible to use monitor mode (without any
transmit) on it when it's otherwise disabled. Add a new
channel flag IEEE80211_CHAN_CAN_MONITOR that makes it
possible for a driver to indicate such a thing.

Make it per channel so drivers could have a choice with
it, perhaps it's only possible on some channels, perhaps
some channels are not supported at all, but still there
and marked disabled.

In _nl80211_parse_chandef() simplify the code and check
only for an unknown channel, _cfg80211_chandef_usable()
will later check for IEEE80211_CHAN_DISABLED anyway.
Signed-off-by: Johannes Berg <johannes.berg@intel.com>
Signed-off-by: Miri Korenblit <miriam.rachel.korenblit@intel.com>
Link: https://msgid.link/20240206164849.87fad3a21a09.I9116b2fdc2e2c9fd59a9273a64db7fcb41fc0328@changeidSigned-off-by: Johannes Berg <johannes.berg@intel.com>

include/net/cfg80211.h

@@ -122,6 +122,9 @@ struct wiphy;
  *	not permitted using this channel
  * @IEEE80211_CHAN_NO_6GHZ_AFC_CLIENT: Client connection with AFC AP
  *	not permitted using this channel
+ * @IEEE80211_CHAN_CAN_MONITOR: This channel can be used for monitor
+ *	mode even in the presence of other (regulatory) restrictions,
+ *	even if it is otherwise disabled.
  */
 enum ieee80211_channel_flags {
 	IEEE80211_CHAN_DISABLED		= 1<<0,
@@ -148,6 +151,7 @@ enum ieee80211_channel_flags {
 	IEEE80211_CHAN_DFS_CONCURRENT	= 1<<21,
 	IEEE80211_CHAN_NO_6GHZ_VLP_CLIENT = 1<<22,
 	IEEE80211_CHAN_NO_6GHZ_AFC_CLIENT = 1<<23,
+	IEEE80211_CHAN_CAN_MONITOR	= 1<<24,
 };
 
 #define IEEE80211_CHAN_NO_HT40 \

include/uapi/linux/nl80211.h

@@ -4273,6 +4273,9 @@ enum nl80211_wmm_rule {
  *	not allowed using this channel
  * @NL80211_FREQUENCY_ATTR_NO_6GHZ_AFC_CLIENT: Client connection to AFC AP
  *	not allowed using this channel
+ * @NL80211_FREQUENCY_ATTR_CAN_MONITOR: This channel can be used in monitor
+ *	mode despite other (regulatory) restrictions, even if the channel is
+ *	otherwise completely disabled.
  * @NL80211_FREQUENCY_ATTR_MAX: highest frequency attribute number
  *	currently defined
  * @__NL80211_FREQUENCY_ATTR_AFTER_LAST: internal use
@@ -4315,6 +4318,7 @@ enum nl80211_frequency_attr {
 	NL80211_FREQUENCY_ATTR_DFS_CONCURRENT,
 	NL80211_FREQUENCY_ATTR_NO_6GHZ_VLP_CLIENT,
 	NL80211_FREQUENCY_ATTR_NO_6GHZ_AFC_CLIENT,
+	NL80211_FREQUENCY_ATTR_CAN_MONITOR,
 
 	/* keep last */
 	__NL80211_FREQUENCY_ATTR_AFTER_LAST,

net/wireless/chan.c

@@ -1145,7 +1145,7 @@ EXPORT_SYMBOL(cfg80211_chandef_dfs_cac_time);
 
 static bool cfg80211_secondary_chans_ok(struct wiphy *wiphy,
 					u32 center_freq, u32 bandwidth,
-					u32 prohibited_flags)
+					u32 prohibited_flags, bool monitor)
 {
 	struct ieee80211_channel *c;
 	u32 freq, start_freq, end_freq;
@@ -1155,7 +1155,11 @@ static bool cfg80211_secondary_chans_ok(struct wiphy *wiphy,
 
 	for (freq = start_freq; freq <= end_freq; freq += MHZ_TO_KHZ(20)) {
 		c = ieee80211_get_channel_khz(wiphy, freq);
-		if (!c || c->flags & prohibited_flags)
+		if (!c)
+			return false;
+		if (monitor && c->flags & IEEE80211_CHAN_CAN_MONITOR)
+			continue;
+		if (c->flags & prohibited_flags)
 			return false;
 	}
 
@@ -1215,9 +1219,9 @@ static bool cfg80211_edmg_usable(struct wiphy *wiphy, u8 edmg_channels,
 	return true;
 }
 
-bool cfg80211_chandef_usable(struct wiphy *wiphy,
+bool _cfg80211_chandef_usable(struct wiphy *wiphy,
 			      const struct cfg80211_chan_def *chandef,
-			     u32 prohibited_flags)
+			      u32 prohibited_flags, bool monitor)
 {
 	struct ieee80211_sta_ht_cap *ht_cap;
 	struct ieee80211_sta_vht_cap *vht_cap;
@@ -1379,14 +1383,22 @@ bool cfg80211_chandef_usable(struct wiphy *wiphy,
 
 	if (!cfg80211_secondary_chans_ok(wiphy,
 					 ieee80211_chandef_to_khz(chandef),
-					 width, prohibited_flags))
+					 width, prohibited_flags, monitor))
 		return false;
 
 	if (!chandef->center_freq2)
 		return true;
 	return cfg80211_secondary_chans_ok(wiphy,
 					   MHZ_TO_KHZ(chandef->center_freq2),
-					   width, prohibited_flags);
+					   width, prohibited_flags, monitor);
+}
+
+bool cfg80211_chandef_usable(struct wiphy *wiphy,
+			     const struct cfg80211_chan_def *chandef,
+			     u32 prohibited_flags)
+{
+	return _cfg80211_chandef_usable(wiphy, chandef, prohibited_flags,
+					false);
 }
 EXPORT_SYMBOL(cfg80211_chandef_usable);
 

net/wireless/core.h

@@ -3,7 +3,7 @@
  * Wireless configuration interface internals.
  *
  * Copyright 2006-2010	Johannes Berg <johannes@sipsolutions.net>
- * Copyright (C) 2018-2023 Intel Corporation
+ * Copyright (C) 2018-2024 Intel Corporation
  */
 #ifndef __NET_WIRELESS_CORE_H
 #define __NET_WIRELESS_CORE_H
@@ -492,6 +492,9 @@ bool cfg80211_is_sub_chan(struct cfg80211_chan_def *chandef,
 bool cfg80211_wdev_on_sub_chan(struct wireless_dev *wdev,
 			       struct ieee80211_channel *chan,
 			       bool primary_only);
+bool _cfg80211_chandef_usable(struct wiphy *wiphy,
+			      const struct cfg80211_chan_def *chandef,
+			      u32 prohibited_flags, bool monitor);
 
 static inline unsigned int elapsed_jiffies_msecs(unsigned long start)
 {

net/wireless/nl80211.c

@@ -3218,8 +3218,8 @@ static bool nl80211_can_set_dev_channel(struct wireless_dev *wdev)
 		wdev->iftype == NL80211_IFTYPE_P2P_GO;
 }
 
-int nl80211_parse_chandef(struct cfg80211_registered_device *rdev,
-			  struct genl_info *info,
+static int _nl80211_parse_chandef(struct cfg80211_registered_device *rdev,
+				  struct genl_info *info, bool monitor,
 				  struct cfg80211_chan_def *chandef)
 {
 	struct netlink_ext_ack *extack = info->extack;
@@ -3245,10 +3245,9 @@ int nl80211_parse_chandef(struct cfg80211_registered_device *rdev,
 	chandef->freq1_offset = control_freq % 1000;
 	chandef->center_freq2 = 0;
 
-	/* Primary channel not allowed */
-	if (!chandef->chan || chandef->chan->flags & IEEE80211_CHAN_DISABLED) {
+	if (!chandef->chan) {
 		NL_SET_ERR_MSG_ATTR(extack, attrs[NL80211_ATTR_WIPHY_FREQ],
-				    "Channel is disabled");
+				    "Unknown channel");
 		return -EINVAL;
 	}
 
@@ -3343,8 +3342,9 @@ int nl80211_parse_chandef(struct cfg80211_registered_device *rdev,
 		return -EINVAL;
 	}
 
-	if (!cfg80211_chandef_usable(&rdev->wiphy, chandef,
-				     IEEE80211_CHAN_DISABLED)) {
+	if (!_cfg80211_chandef_usable(&rdev->wiphy, chandef,
+				      IEEE80211_CHAN_DISABLED,
+				      monitor)) {
 		NL_SET_ERR_MSG(extack, "(extension) channel is disabled");
 		return -EINVAL;
 	}
@@ -3359,6 +3359,13 @@ int nl80211_parse_chandef(struct cfg80211_registered_device *rdev,
 	return 0;
 }
 
+int nl80211_parse_chandef(struct cfg80211_registered_device *rdev,
+			  struct genl_info *info,
+			  struct cfg80211_chan_def *chandef)
+{
+	return _nl80211_parse_chandef(rdev, info, false, chandef);
+}
+
 static int __nl80211_set_channel(struct cfg80211_registered_device *rdev,
 				 struct net_device *dev,
 				 struct genl_info *info,
@@ -3383,7 +3390,9 @@ static int __nl80211_set_channel(struct cfg80211_registered_device *rdev,
 		link_id = 0;
 	}
 
-	result = nl80211_parse_chandef(rdev, info, &chandef);
+	result = _nl80211_parse_chandef(rdev, info,
+					iftype == NL80211_IFTYPE_MONITOR,
+					&chandef);
 	if (result)
 		return result;