cfg80211: validate channel settings across interfaces

Currently, there's a problem that affects regulatory
enforcement and connection stability, in that it is
possible to switch the channel while connected to a
network or joined to an IBSS.

The problem comes from the fact that we only validate
the channel against the current interface's type, not
against any other interface. Thus, you have any type
of interface up, additionally bring up a monitor mode
interface and switch the channel on the monitor. This
will obviously also switch the channel on the other
interface.

The problem now is that if you do that while sending
beacons for IBSS mode, you can switch to a disabled
channel or a channel that doesn't allow beaconing.
Combined with a managed mode interface connected to
an AP instead of an IBSS interface, you can easily
break the connection that way.

To fix this, this patch validates any channel change
with all available interfaces, and disallows such
changes on secondary interfaces if another interface
is connected to an AP or joined to an IBSS.

Signed-off-by: Johannes Berg <johannes@sipsolutions.net>
Signed-off-by: John W. Linville <linville@tuxdriver.com>

1 files changed, 88 insertions, 0 deletions

diff --git a/net/wireless/chan.c b/net/wireless/chan.c
new file mode 100644
index 0000000..bc00c9a
--- /dev/null
+++ b/net/wireless/chan.c
@@ -0,0 +1,88 @@
+/*
+ * This file contains helper code to handle channel
+ * settings and keeping track of what is possible at
+ * any point in time.
+ *
+ * Copyright 2009	Johannes Berg <johannes@sipsolutions.net>
+ */
+
+#include <net/cfg80211.h>
+#include "core.h"
+
+struct ieee80211_channel *
+rdev_fixed_channel(struct cfg80211_registered_device *rdev,
+		   struct wireless_dev *for_wdev)
+{
+	struct wireless_dev *wdev;
+	struct ieee80211_channel *result = NULL;
+
+	WARN_ON(!mutex_is_locked(&rdev->devlist_mtx));
+
+	list_for_each_entry(wdev, &rdev->netdev_list, list) {
+		if (wdev == for_wdev)
+			continue;
+
+		/*
+		 * Lock manually to tell lockdep about allowed
+		 * nesting here if for_wdev->mtx is held already.
+		 * This is ok as it's all under the rdev devlist
+		 * mutex and as such can only be done once at any
+		 * given time.
+		 */
+		mutex_lock_nested(&wdev->mtx, SINGLE_DEPTH_NESTING);
+		if (wdev->current_bss)
+			result = wdev->current_bss->pub.channel;
+		wdev_unlock(wdev);
+
+		if (result)
+			break;
+	}
+
+	return result;
+}
+
+int rdev_set_freq(struct cfg80211_registered_device *rdev,
+		  int freq, enum nl80211_channel_type channel_type)
+{
+	struct ieee80211_channel *chan;
+	struct ieee80211_sta_ht_cap *ht_cap;
+	int result;
+
+	if (rdev_fixed_channel(rdev, NULL))
+		return -EBUSY;
+
+	if (!rdev->ops->set_channel)
+		return -EOPNOTSUPP;
+
+	chan = ieee80211_get_channel(&rdev->wiphy, freq);
+
+	/* Primary channel not allowed */
+	if (!chan || chan->flags & IEEE80211_CHAN_DISABLED)
+		return -EINVAL;
+
+	if (channel_type == NL80211_CHAN_HT40MINUS &&
+	    chan->flags & IEEE80211_CHAN_NO_HT40MINUS)
+		return -EINVAL;
+	else if (channel_type == NL80211_CHAN_HT40PLUS &&
+		 chan->flags & IEEE80211_CHAN_NO_HT40PLUS)
+		return -EINVAL;
+
+	ht_cap = &rdev->wiphy.bands[chan->band]->ht_cap;
+
+	if (channel_type != NL80211_CHAN_NO_HT) {
+		if (!ht_cap->ht_supported)
+			return -EINVAL;
+
+		if (!(ht_cap->cap & IEEE80211_HT_CAP_SUP_WIDTH_20_40) ||
+		    ht_cap->cap & IEEE80211_HT_CAP_40MHZ_INTOLERANT)
+			return -EINVAL;
+	}
+
+	result = rdev->ops->set_channel(&rdev->wiphy, chan, channel_type);
+	if (result)
+		return result;
+
+	rdev->channel = chan;
+
+	return 0;
+}