nl80211/cfg80211: enable DFS for IBSS mode

To use DFS in IBSS mode, userspace is required to react to radar events.
It can inform nl80211 that it is capable of doing so by adding a
NL80211_ATTR_HANDLE_DFS attribute when joining the IBSS.

This attribute is supplied to let the kernelspace know that the
userspace application can and will handle radar events, e.g. by
intiating channel switches to a valid channel. DFS channels may
only be used if this attribute is supplied and the driver supports
it. Driver support will be checked even if a channel without DFS
will be initially joined, as a DFS channel may be chosen later.

Signed-off-by: Simon Wunderlich <[e-mail]>
Signed-off-by: Mathias Kretschmer <[e-mail]>
[fix attribute name in commit message]
Signed-off-by: Johannes Berg <[e-mail]>

include/net/cfg80211.h

···
  *	sets/clears %NL80211_STA_FLAG_AUTHORIZED. If true, the driver is
  *	required to assume that the port is unauthorized until authorized by
  *	user space. Otherwise, port is marked authorized by default.
+ * @userspace_handles_dfs: whether user space controls DFS operation, i.e.
+ *	changes the channel when a radar is detected. This is required
+ *	to operate on DFS channels.
  * @basic_rates: bitmap of basic rates to use when creating the IBSS
  * @mcast_rate: per-band multicast rate index + 1 (0: disabled)
  * @ht_capa:  HT Capabilities over-rides.  Values set in ht_capa_mask
···
 	bool channel_fixed;
 	bool privacy;
 	bool control_port;
+	bool userspace_handles_dfs;
 	int mcast_rate[IEEE80211_NUM_BANDS];
 	struct ieee80211_ht_cap ht_capa;
 	struct ieee80211_ht_cap ht_capa_mask;
···
  * @conn: (private) cfg80211 software SME connection state machine data
  * @connect_keys: (private) keys to set after connection is established
  * @ibss_fixed: (private) IBSS is using fixed BSSID
+ * @ibss_dfs_possible: (private) IBSS may change to a DFS channel
  * @event_list: (private) list for internal event processing
  * @event_lock: (private) lock for event list
  */
···
 	struct ieee80211_channel *channel;
 
 	bool ibss_fixed;
+	bool ibss_dfs_possible;
 
 	bool ps;
 	int ps_timeout;

include/uapi/linux/nl80211.h

···
  * @NL80211_ATTR_STA_SUPPORTED_OPER_CLASSES: array of supported
  *      supported operating classes.
  *
+ * @NL80211_ATTR_HANDLE_DFS: A flag indicating whether user space
+ *	controls DFS operation in IBSS mode. If the flag is included in
+ *	%NL80211_CMD_JOIN_IBSS request, the driver will allow use of DFS
+ *	channels and reports radar events to userspace. Userspace is required
+ *	to react to radar events, e.g. initiate a channel switch or leave the
+ *	IBSS network.
+ *
  * @NL80211_ATTR_MAX: highest attribute number currently defined
  * @__NL80211_ATTR_AFTER_LAST: internal use
  */
···
 	NL80211_ATTR_STA_SUPPORTED_CHANNELS,
 
 	NL80211_ATTR_STA_SUPPORTED_OPER_CLASSES,
+
+	NL80211_ATTR_HANDLE_DFS,
 
 	/* add attributes here, update the policy in nl80211.c */
 

net/wireless/chan.c

···
 	case NL80211_IFTYPE_ADHOC:
 		if (wdev->current_bss) {
 			*chan = wdev->current_bss->pub.channel;
-			*chanmode = wdev->ibss_fixed
+			*chanmode = (wdev->ibss_fixed &&
+				     !wdev->ibss_dfs_possible)
 				  ? CHAN_MODE_SHARED
 				  : CHAN_MODE_EXCLUSIVE;
 			return;

net/wireless/ibss.c

···
 			 struct cfg80211_cached_keys *connkeys)
 {
 	struct wireless_dev *wdev = dev->ieee80211_ptr;
+	struct ieee80211_channel *check_chan;
+	u8 radar_detect_width = 0;
 	int err;
 
 	ASSERT_WDEV_LOCK(wdev);
···
 	wdev->connect_keys = connkeys;
 
 	wdev->ibss_fixed = params->channel_fixed;
+	wdev->ibss_dfs_possible = params->userspace_handles_dfs;
 #ifdef CONFIG_CFG80211_WEXT
 	wdev->wext.ibss.chandef = params->chandef;
 #endif
+	check_chan = params->chandef.chan;
+	if (params->userspace_handles_dfs) {
+		/* use channel NULL to check for radar even if the current
+		 * channel is not a radar channel - it might decide to change
+		 * to DFS channel later.
+		 */
+		radar_detect_width = BIT(params->chandef.width);
+		check_chan = NULL;
+	}
 
-	err = cfg80211_can_use_chan(rdev, wdev, params->chandef.chan,
-				    params->channel_fixed
-				    ? CHAN_MODE_SHARED
-				    : CHAN_MODE_EXCLUSIVE);
+	err = cfg80211_can_use_iftype_chan(rdev, wdev, wdev->iftype,
+					   check_chan,
+					   (params->channel_fixed &&
+					    !radar_detect_width)
+					   ? CHAN_MODE_SHARED
+					   : CHAN_MODE_EXCLUSIVE,
+					   radar_detect_width);
+
 	if (err) {
 		wdev->connect_keys = NULL;
 		return err;

net/wireless/nl80211.c

···
 	[NL80211_ATTR_CSA_C_OFF_PRESP] = { .type = NLA_U16 },
 	[NL80211_ATTR_STA_SUPPORTED_CHANNELS] = { .type = NLA_BINARY },
 	[NL80211_ATTR_STA_SUPPORTED_OPER_CLASSES] = { .type = NLA_BINARY },
+	[NL80211_ATTR_HANDLE_DFS] = { .type = NLA_FLAG },
 };
 
 /* policy for the key attributes */
···
 	if (!cfg80211_reg_can_beacon(&rdev->wiphy, &params.chandef))
 		return -EINVAL;
 
-	/* DFS channels are only supported for AP/P2P GO ... for now. */
 	if (dev->ieee80211_ptr->iftype == NL80211_IFTYPE_AP ||
-	    dev->ieee80211_ptr->iftype == NL80211_IFTYPE_P2P_GO) {
+	    dev->ieee80211_ptr->iftype == NL80211_IFTYPE_P2P_GO ||
+	    dev->ieee80211_ptr->iftype == NL80211_IFTYPE_ADHOC) {
 		err = cfg80211_chandef_dfs_required(wdev->wiphy,
 						    &params.chandef);
 		if (err < 0) {
···
 
 	ibss.control_port =
 		nla_get_flag(info->attrs[NL80211_ATTR_CONTROL_PORT]);
+
+	ibss.userspace_handles_dfs =
+		nla_get_flag(info->attrs[NL80211_ATTR_HANDLE_DFS]);
 
 	err = cfg80211_join_ibss(rdev, dev, &ibss, connkeys);
 	if (err)

net/wireless/util.c

···
 	enum cfg80211_chan_mode chmode;
 	int num_different_channels = 0;
 	int total = 1;
-	bool radar_required;
+	bool radar_required = false;
 	int i, j;
 
 	ASSERT_RTNL();
···
 	case NL80211_IFTYPE_MESH_POINT:
 	case NL80211_IFTYPE_P2P_GO:
 	case NL80211_IFTYPE_WDS:
-		radar_required = !!(chan &&
-				    (chan->flags & IEEE80211_CHAN_RADAR));
+		/* if the interface could potentially choose a DFS channel,
+		 * then mark DFS as required.
+		 */
+		if (!chan) {
+			if (chanmode != CHAN_MODE_UNDEFINED && radar_detect)
+				radar_required = true;
+			break;
+		}
+		radar_required = !!(chan->flags & IEEE80211_CHAN_RADAR);
 		break;
 	case NL80211_IFTYPE_P2P_CLIENT:
 	case NL80211_IFTYPE_STATION:
 	case NL80211_IFTYPE_P2P_DEVICE:
 	case NL80211_IFTYPE_MONITOR:
-		radar_required = false;
 		break;
 	case NUM_NL80211_IFTYPES:
 	case NL80211_IFTYPE_UNSPECIFIED: