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 <siwu@hrz.tu-chemnitz.de>
Signed-off-by: Mathias Kretschmer <mathias.kretschmer@fokus.fraunhofer.de>
[fix attribute name in commit message]
Signed-off-by: Johannes Berg <johannes.berg@intel.com>

4 files changed, 38 insertions, 11 deletions

diff --git a/net/wireless/chan.c b/net/wireless/chan.c
index 16f3c3a..9b8cc87 100644
--- a/net/wireless/chan.c
+++ b/net/wireless/chan.c
@@ -504,7 +504,8 @@ cfg80211_get_chan_state(struct wireless_dev *wdev,
 	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;
diff --git a/net/wireless/ibss.c b/net/wireless/ibss.c
index 39bff7d..fa7461b 100644
--- a/net/wireless/ibss.c
+++ b/net/wireless/ibss.c
@@ -83,6 +83,8 @@ int __cfg80211_join_ibss(struct cfg80211_registered_device *rdev,
 			 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);
@@ -114,14 +116,28 @@ int __cfg80211_join_ibss(struct cfg80211_registered_device *rdev,
 	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_iftype_chan(rdev, wdev, wdev->iftype,
+					   check_chan,
+					   (params->channel_fixed &&
+					    !radar_detect_width)
+					   ? CHAN_MODE_SHARED
+					   : CHAN_MODE_EXCLUSIVE,
+					   radar_detect_width);
 
-	err = cfg80211_can_use_chan(rdev, wdev, params->chandef.chan,
-				    params->channel_fixed
-				    ? CHAN_MODE_SHARED
-				    : CHAN_MODE_EXCLUSIVE);
 	if (err) {
 		wdev->connect_keys = NULL;
 		return err;
diff --git a/net/wireless/nl80211.c b/net/wireless/nl80211.c
index 460638a..7502d33 100644
--- a/net/wireless/nl80211.c
+++ b/net/wireless/nl80211.c
@@ -356,6 +356,7 @@ static const struct nla_policy nl80211_policy[NL80211_ATTR_MAX+1] = {
 	[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 */
@@ -5768,9 +5769,9 @@ skip_beacons:
 	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) {
@@ -6602,6 +6603,9 @@ static int nl80211_join_ibss(struct sk_buff *skb, struct genl_info *info)
 	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)
 		kfree(connkeys);
diff --git a/net/wireless/util.c b/net/wireless/util.c
index 3c8be61..935dea9 100644
--- a/net/wireless/util.c
+++ b/net/wireless/util.c
@@ -1249,7 +1249,7 @@ int cfg80211_can_use_iftype_chan(struct cfg80211_registered_device *rdev,
 	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();
@@ -1264,14 +1264,20 @@ int cfg80211_can_use_iftype_chan(struct cfg80211_registered_device *rdev,
 	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: