cfg80211/mac80211: better channel handling

Currently (all tested with hwsim) you can do stupid
things like setting up an AP on a certain channel,
then adding another virtual interface and making
that associate on another channel -- this will make
the beaconing to move channel but obviously without
the necessary IEs data update.

In order to improve this situation, first make the
configuration APIs (cfg80211 and nl80211) aware of
multi-channel operation -- we'll eventually need
that in the future anyway. There's one userland API
change and one API addition. The API change is that
now SET_WIPHY must be called with virtual interface
index rather than only wiphy index in order to take
effect for that interface -- luckily all current
users (hostapd) do that. For monitor interfaces, the
old setting is preserved, but monitors are always
slaved to other devices anyway so no guarantees.

The second userland API change is the introduction
of a per virtual interface SET_CHANNEL command, that
hostapd should use going forward to make it easier
to understand what's going on (it can automatically
detect a kernel with this command).

Other than mac80211, no existing cfg80211 drivers
are affected by this change because they only allow
a single virtual interface.

mac80211, however, now needs to be aware that the
channel settings are per interface now, and needs
to disallow (for now) real multi-channel operation,
which is another important part of this patch.

One of the immediate benefits is that you can now
start hostapd to operate on a hardware that already
has a connection on another virtual interface, as
long as you specify the same channel.

Note that two things are left unhandled (this is an
improvement -- not a complete fix):

 * different HT/no-HT modes

   currently you could start an HT AP and then
   connect to a non-HT network on the same channel
   which would configure the hardware for no HT;
   that can be fixed fairly easily

 * CSA

   An AP we're connected to on a virtual interface
   might indicate switching channels, and in that
   case we would follow it, regardless of how many
   other interfaces are operating; this requires
   more effort to fix but is pretty rare after all

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

1 files changed, 41 insertions, 0 deletions

diff --git a/net/mac80211/cfg.c b/net/mac80211/cfg.c
index b575a5066219..414b7dd7d7fd 100644
--- a/net/mac80211/cfg.c
+++ b/net/mac80211/cfg.c
@@ -1161,11 +1161,24 @@ static int ieee80211_set_txq_params(struct wiphy *wiphy,
 }
 
 static int ieee80211_set_channel(struct wiphy *wiphy,
+                                 struct net_device *netdev,
                                  struct ieee80211_channel *chan,
                                  enum nl80211_channel_type channel_type)
 {
         struct ieee80211_local *local = wiphy_priv(wiphy);
 
+        switch (ieee80211_get_channel_mode(local, NULL)) {
+        case CHAN_MODE_HOPPING:
+                return -EBUSY;
+        case CHAN_MODE_FIXED:
+                if (local->oper_channel == chan &&
+                    local->oper_channel_type == channel_type)
+                        return 0;
+                return -EBUSY;
+        case CHAN_MODE_UNDEFINED:
+                break;
+        }
+
         local->oper_channel = chan;
         local->oper_channel_type = channel_type;
 
@@ -1213,6 +1226,20 @@ static int ieee80211_auth(struct wiphy *wiphy, struct net_device *dev,
 static int ieee80211_assoc(struct wiphy *wiphy, struct net_device *dev,
                            struct cfg80211_assoc_request *req)
 {
+        struct ieee80211_local *local = wiphy_priv(wiphy);
+        struct ieee80211_sub_if_data *sdata = IEEE80211_DEV_TO_SUB_IF(dev);
+
+        switch (ieee80211_get_channel_mode(local, sdata)) {
+        case CHAN_MODE_HOPPING:
+                return -EBUSY;
+        case CHAN_MODE_FIXED:
+                if (local->oper_channel == req->bss->channel)
+                        break;
+                return -EBUSY;
+        case CHAN_MODE_UNDEFINED:
+                break;
+        }
+
         return ieee80211_mgd_assoc(IEEE80211_DEV_TO_SUB_IF(dev), req);
 }
 
@@ -1235,8 +1262,22 @@ static int ieee80211_disassoc(struct wiphy *wiphy, struct net_device *dev,
 static int ieee80211_join_ibss(struct wiphy *wiphy, struct net_device *dev,
                                struct cfg80211_ibss_params *params)
 {
+        struct ieee80211_local *local = wiphy_priv(wiphy);
         struct ieee80211_sub_if_data *sdata = IEEE80211_DEV_TO_SUB_IF(dev);
 
+        switch (ieee80211_get_channel_mode(local, sdata)) {
+        case CHAN_MODE_HOPPING:
+                return -EBUSY;
+        case CHAN_MODE_FIXED:
+                if (!params->channel_fixed)
+                        return -EBUSY;
+                if (local->oper_channel == params->channel)
+                        break;
+                return -EBUSY;
+        case CHAN_MODE_UNDEFINED:
+                break;
+        }
+
         return ieee80211_ibss_join(sdata, params);
 }