mac80211: implement support for 4-address frames for AP and client mode

In some situations it might be useful to run a network with an
Access Point and multiple clients, but with each client bridged
to a network behind it. For this to work, both the client and the
AP need to transmit 4-address frames, containing both source and
destination MAC addresses.
With this patch, you can configure a client to communicate using
only 4-address frames for data traffic.
On the AP side you can enable 4-address frames for individual
clients by isolating them in separate AP VLANs which are configured
in 4-address mode.
Such an AP VLAN will be limited to one client only, and this client
will be used as the destination for all traffic on its interface,
regardless of the destination MAC address in the packet headers.
The advantage of this mode compared to regular WDS mode is that it's
easier to configure and does not require a static list of peer MAC
addresses on any side.

Signed-off-by: Felix Fietkau <nbd@openwrt.org>
Signed-off-by: John W. Linville <linville@tuxdriver.com>

1 files changed, 30 insertions, 2 deletions

diff --git a/net/mac80211/cfg.c b/net/mac80211/cfg.c
index 56319b51d170..576b86f81d1b 100644
--- a/net/mac80211/cfg.c
+++ b/net/mac80211/cfg.c
@@ -36,6 +36,24 @@ static bool nl80211_type_check(enum nl80211_iftype type)
         }
 }
 
+static bool nl80211_params_check(enum nl80211_iftype type,
+                                 struct vif_params *params)
+{
+        if (!nl80211_type_check(type))
+                return false;
+
+        if (params->use_4addr > 0) {
+                switch(type) {
+                case NL80211_IFTYPE_AP_VLAN:
+                case NL80211_IFTYPE_STATION:
+                        break;
+                default:
+                        return false;
+                }
+        }
+        return true;
+}
+
 static int ieee80211_add_iface(struct wiphy *wiphy, char *name,
                                enum nl80211_iftype type, u32 *flags,
                                struct vif_params *params)
@@ -45,7 +63,7 @@ static int ieee80211_add_iface(struct wiphy *wiphy, char *name,
         struct ieee80211_sub_if_data *sdata;
         int err;
 
-        if (!nl80211_type_check(type))
+        if (!nl80211_params_check(type, params))
                 return -EINVAL;
 
         err = ieee80211_if_add(local, name, &dev, type, params);
@@ -75,7 +93,7 @@ static int ieee80211_change_iface(struct wiphy *wiphy,
         if (netif_running(dev))
                 return -EBUSY;
 
-        if (!nl80211_type_check(type))
+        if (!nl80211_params_check(type, params))
                 return -EINVAL;
 
         sdata = IEEE80211_DEV_TO_SUB_IF(dev);
@@ -89,6 +107,9 @@ static int ieee80211_change_iface(struct wiphy *wiphy,
                                             params->mesh_id_len,
                                             params->mesh_id);
 
+        if (params->use_4addr >= 0)
+                sdata->use_4addr = !!params->use_4addr;
+
         if (sdata->vif.type != NL80211_IFTYPE_MONITOR || !flags)
                 return 0;
 
@@ -806,6 +827,13 @@ static int ieee80211_change_station(struct wiphy *wiphy,
                         return -EINVAL;
                 }
 
+                if (vlansdata->use_4addr) {
+                        if (vlansdata->u.vlan.sta)
+                                return -EBUSY;
+
+                        rcu_assign_pointer(vlansdata->u.vlan.sta, sta);
+                }
+
                 sta->sdata = vlansdata;
                 ieee80211_send_layer2_update(sta);
         }