cfg80211: allow leaving MU-MIMO monitor configuration unchanged

When changing monitor parameters, not setting the MU-MIMO attributes
should mean that they're not changed - it's documented that to turn
the feature off it's necessary to set all-zero group membership and
an invalid follow-address. This isn't implemented.

Fix this by making the parameters pointers, stop reusing the macaddr
struct member, and documenting that NULL pointers mean unchanged.
Signed-off-by: NJohannes Berg <johannes.berg@intel.com>

include/net/cfg80211.h

@@ -370,13 +370,16 @@ static inline void wiphy_read_of_freq_limits(struct wiphy *wiphy)
  *	This feature is only fully supported by drivers that enable the
  *	%NL80211_FEATURE_MAC_ON_CREATE flag.  Others may support creating
  **	only p2p devices with specified MAC.
- * @vht_mumimo_groups: MU-MIMO groupID. used for monitoring only
- *	 packets belonging to that MU-MIMO groupID.
+ * @vht_mumimo_groups: MU-MIMO groupID, used for monitoring MU-MIMO packets
+ *	belonging to that MU-MIMO groupID; %NULL if not changed
+ * @vht_mumimo_follow_addr: MU-MIMO follow address, used for monitoring
+ *	MU-MIMO packets going to the specified station; %NULL if not changed
  */
 struct vif_params {
 	int use_4addr;
 	u8 macaddr[ETH_ALEN];
-	u8 vht_mumimo_groups[VHT_MUMIMO_GROUPS_DATA_LEN];
+	const u8 *vht_mumimo_groups;
+	const u8 *vht_mumimo_follow_addr;
 };
 
 /**

net/mac80211/cfg.c

@@ -80,8 +80,7 @@ static int ieee80211_change_iface(struct wiphy *wiphy,
 		u32 mu_mntr_cap_flag = NL80211_EXT_FEATURE_MU_MIMO_AIR_SNIFFER;
 
 		monitor_sdata = rtnl_dereference(local->monitor_sdata);
-		if (monitor_sdata &&
-		    wiphy_ext_feature_isset(wiphy, mu_mntr_cap_flag)) {
+		if (monitor_sdata && params->vht_mumimo_groups) {
 			memcpy(monitor_sdata->vif.bss_conf.mu_group.membership,
 			       params->vht_mumimo_groups, WLAN_MEMBERSHIP_LEN);
 			memcpy(monitor_sdata->vif.bss_conf.mu_group.position,
@@ -90,10 +89,11 @@ static int ieee80211_change_iface(struct wiphy *wiphy,
 			monitor_sdata->vif.mu_mimo_owner = true;
 			ieee80211_bss_info_change_notify(monitor_sdata,
 							 BSS_CHANGED_MU_GROUPS);
+		}
 
+		if (monitor_sdata && params->vht_mumimo_follow_addr)
 			ether_addr_copy(monitor_sdata->u.mntr.mu_follow_addr,
-					params->macaddr);
-		}
+					params->vht_mumimo_follow_addr);
 
 		if (!flags)
 			return 0;

net/wireless/nl80211.c

@@ -2832,8 +2832,7 @@ static int nl80211_set_interface(struct sk_buff *skb, struct genl_info *info)
 		    (mumimo_groups[VHT_MUMIMO_GROUPS_DATA_LEN - 1] & BIT(0)))
 			return -EINVAL;
 
-		memcpy(params.vht_mumimo_groups, mumimo_groups,
-		       VHT_MUMIMO_GROUPS_DATA_LEN);
+		params.vht_mumimo_groups = mumimo_groups;
 		change = true;
 	}
 
@@ -2843,9 +2842,8 @@ static int nl80211_set_interface(struct sk_buff *skb, struct genl_info *info)
 		if (!wiphy_ext_feature_isset(&rdev->wiphy, cap_flag))
 			return -EOPNOTSUPP;
 
-		nla_memcpy(params.macaddr,
-			   info->attrs[NL80211_ATTR_MU_MIMO_FOLLOW_MAC_ADDR],
-			   ETH_ALEN);
+		params.vht_mumimo_follow_addr =
+			nla_data(info->attrs[NL80211_ATTR_MU_MIMO_FOLLOW_MAC_ADDR]);
 		change = true;
 	}