cfg80211: support an active monitor interface flag

An active monitor interface is one that is used for communication (via
injection). It is expected to ACK incoming unicast packets. This is
useful for running various 802.11 testing utilities that associate to an
AP via injection and manage the state in user space.
Signed-off-by: Felix Fietkau <nbd@openwrt.org>
Signed-off-by: Johannes Berg <johannes.berg@intel.com>

include/net/cfg80211.h

@@ -961,6 +961,7 @@ struct station_info {
  * @MONITOR_FLAG_CONTROL: pass control frames
  * @MONITOR_FLAG_OTHER_BSS: disable BSSID filtering
  * @MONITOR_FLAG_COOK_FRAMES: report frames after processing
+ * @MONITOR_FLAG_ACTIVE: active monitor, ACKs frames on its MAC address
  */
 enum monitor_flags {
 	MONITOR_FLAG_FCSFAIL		= 1<<NL80211_MNTR_FLAG_FCSFAIL,
@@ -968,6 +969,7 @@ enum monitor_flags {
 	MONITOR_FLAG_CONTROL		= 1<<NL80211_MNTR_FLAG_CONTROL,
 	MONITOR_FLAG_OTHER_BSS		= 1<<NL80211_MNTR_FLAG_OTHER_BSS,
 	MONITOR_FLAG_COOK_FRAMES	= 1<<NL80211_MNTR_FLAG_COOK_FRAMES,
+	MONITOR_FLAG_ACTIVE		= 1<<NL80211_MNTR_FLAG_ACTIVE,
 };
 
 /**

include/uapi/linux/nl80211.h

@@ -2428,6 +2428,8 @@ enum nl80211_survey_info {
  * @NL80211_MNTR_FLAG_OTHER_BSS: disable BSSID filtering
  * @NL80211_MNTR_FLAG_COOK_FRAMES: report frames after processing.
  *	overrides all other flags.
+ * @NL80211_MNTR_FLAG_ACTIVE: use the configured MAC address
+ *	and ACK incoming unicast packets.
  *
  * @__NL80211_MNTR_FLAG_AFTER_LAST: internal use
  * @NL80211_MNTR_FLAG_MAX: highest possible monitor flag
@@ -2439,6 +2441,7 @@ enum nl80211_mntr_flags {
 	NL80211_MNTR_FLAG_CONTROL,
 	NL80211_MNTR_FLAG_OTHER_BSS,
 	NL80211_MNTR_FLAG_COOK_FRAMES,
+	NL80211_MNTR_FLAG_ACTIVE,
 
 	/* keep last */
 	__NL80211_MNTR_FLAG_AFTER_LAST,
@@ -3595,6 +3598,7 @@ enum nl80211_feature_flags {
 	NL80211_FEATURE_ADVERTISE_CHAN_LIMITS		= 1 << 14,
 	NL80211_FEATURE_FULL_AP_CLIENT_STATE		= 1 << 15,
 	NL80211_FEATURE_USERSPACE_MPM			= 1 << 16,
+	NL80211_FEATURE_ACTIVE_MONITOR			= 1 << 17,
 };
 
 /**

net/wireless/nl80211.c

@@ -2227,6 +2227,7 @@ static const struct nla_policy mntr_flags_policy[NL80211_MNTR_FLAG_MAX + 1] = {
 	[NL80211_MNTR_FLAG_CONTROL] = { .type = NLA_FLAG },
 	[NL80211_MNTR_FLAG_OTHER_BSS] = { .type = NLA_FLAG },
 	[NL80211_MNTR_FLAG_COOK_FRAMES] = { .type = NLA_FLAG },
+	[NL80211_MNTR_FLAG_ACTIVE] = { .type = NLA_FLAG },
 };
 
 static int parse_monitor_flags(struct nlattr *nla, u32 *mntrflags)
@@ -2338,6 +2339,10 @@ static int nl80211_set_interface(struct sk_buff *skb, struct genl_info *info)
 		change = true;
 	}
 
+	if (flags && (*flags & NL80211_MNTR_FLAG_ACTIVE) &&
+	    !(rdev->wiphy.features & NL80211_FEATURE_ACTIVE_MONITOR))
+		return -EOPNOTSUPP;
+
 	if (change)
 		err = cfg80211_change_iface(rdev, dev, ntype, flags, &params);
 	else
@@ -2395,6 +2400,11 @@ static int nl80211_new_interface(struct sk_buff *skb, struct genl_info *info)
 	err = parse_monitor_flags(type == NL80211_IFTYPE_MONITOR ?
 				  info->attrs[NL80211_ATTR_MNTR_FLAGS] : NULL,
 				  &flags);
+
+	if (!err && (flags & NL80211_MNTR_FLAG_ACTIVE) &&
+	    !(rdev->wiphy.features & NL80211_FEATURE_ACTIVE_MONITOR))
+		return -EOPNOTSUPP;
+
 	wdev = rdev_add_virtual_intf(rdev,
 				nla_data(info->attrs[NL80211_ATTR_IFNAME]),
 				type, err ? NULL : &flags, &params);