cfg80211: configure multicast to unicast for AP interfaces

Add the ability to configure if an AP (and associated VLANs) will
do multicast-to-unicast conversion for ARP, IPv4 and IPv6 frames
(possibly within 802.1Q). If enabled, such frames are to be sent
to each station separately, with the DA replaced by their own MAC
address rather than the group address.

Note that this may break certain expectations of the receiver,
such as the ability to drop unicast IP packets received within
multicast L2 frames, or the ability to not send ICMP destination
unreachable messages for packets received in L2 multicast (which
is required, but the receiver can't tell the difference if this
new option is enabled.)

This also doesn't implement the 802.11 DMS (directed multicast
service).

Signed-off-by: Michael Braun <michael-dev@fami-braun.de>
[fix disabling, add better documentation & commit message]
Signed-off-by: Johannes Berg <johannes.berg@intel.com>

3 files changed, 66 insertions, 0 deletions

diff --git a/net/wireless/nl80211.c b/net/wireless/nl80211.c
index 667d5f7..0c9d00c9 100644
--- a/net/wireless/nl80211.c
+++ b/net/wireless/nl80211.c
@@ -417,6 +417,7 @@ static const struct nla_policy nl80211_policy[NUM_NL80211_ATTR] = {
 	[NL80211_ATTR_FILS_KEK] = { .type = NLA_BINARY,
 				    .len = FILS_MAX_KEK_LEN },
 	[NL80211_ATTR_FILS_NONCES] = { .len = 2 * FILS_NONCE_LEN },
+	[NL80211_ATTR_MULTICAST_TO_UNICAST_ENABLED] = { .type = NLA_FLAG, },
 };
 
 /* policy for the key attributes */
@@ -1659,6 +1660,7 @@ static int nl80211_send_wiphy(struct cfg80211_registered_device *rdev,
 			if (rdev->wiphy.features &
 					NL80211_FEATURE_SUPPORTS_WMM_ADMISSION)
 				CMD(add_tx_ts, ADD_TX_TS);
+			CMD(set_multicast_to_unicast, SET_MULTICAST_TO_UNICAST);
 		}
 #undef CMD
 
@@ -11766,6 +11768,31 @@ static int nl80211_tdls_cancel_channel_switch(struct sk_buff *skb,
 	return 0;
 }
 
+static int nl80211_set_multicast_to_unicast(struct sk_buff *skb,
+					    struct genl_info *info)
+{
+	struct cfg80211_registered_device *rdev = info->user_ptr[0];
+	struct net_device *dev = info->user_ptr[1];
+	struct wireless_dev *wdev = dev->ieee80211_ptr;
+	const struct nlattr *nla;
+	bool enabled;
+
+	if (netif_running(dev))
+		return -EBUSY;
+
+	if (!rdev->ops->set_multicast_to_unicast)
+		return -EOPNOTSUPP;
+
+	if (wdev->iftype != NL80211_IFTYPE_AP &&
+	    wdev->iftype != NL80211_IFTYPE_P2P_GO)
+		return -EOPNOTSUPP;
+
+	nla = info->attrs[NL80211_ATTR_MULTICAST_TO_UNICAST_ENABLED];
+	enabled = nla_get_flag(nla);
+
+	return rdev_set_multicast_to_unicast(rdev, dev, enabled);
+}
+
 #define NL80211_FLAG_NEED_WIPHY		0x01
 #define NL80211_FLAG_NEED_NETDEV	0x02
 #define NL80211_FLAG_NEED_RTNL		0x04
@@ -12625,6 +12652,14 @@ static const struct genl_ops nl80211_ops[] = {
 		.internal_flags = NL80211_FLAG_NEED_NETDEV_UP |
 				  NL80211_FLAG_NEED_RTNL,
 	},
+	{
+		.cmd = NL80211_CMD_SET_MULTICAST_TO_UNICAST,
+		.doit = nl80211_set_multicast_to_unicast,
+		.policy = nl80211_policy,
+		.flags = GENL_UNS_ADMIN_PERM,
+		.internal_flags = NL80211_FLAG_NEED_NETDEV |
+				  NL80211_FLAG_NEED_RTNL,
+	},
 };
 
 /* notification functions */
diff --git a/net/wireless/rdev-ops.h b/net/wireless/rdev-ops.h
index 11cf83c..e9ecf23 100644
--- a/net/wireless/rdev-ops.h
+++ b/net/wireless/rdev-ops.h
@@ -562,6 +562,18 @@ static inline int rdev_set_wds_peer(struct cfg80211_registered_device *rdev,
 	return ret;
 }
 
+static inline int
+rdev_set_multicast_to_unicast(struct cfg80211_registered_device *rdev,
+			      struct net_device *dev,
+			      const bool enabled)
+{
+	int ret;
+	trace_rdev_set_multicast_to_unicast(&rdev->wiphy, dev, enabled);
+	ret = rdev->ops->set_multicast_to_unicast(&rdev->wiphy, dev, enabled);
+	trace_rdev_return_int(&rdev->wiphy, ret);
+	return ret;
+}
+
 static inline void rdev_rfkill_poll(struct cfg80211_registered_device *rdev)
 {
 	trace_rdev_rfkill_poll(&rdev->wiphy);
diff --git a/net/wireless/trace.h b/net/wireless/trace.h
index a3d0a91b..25f8318 100644
--- a/net/wireless/trace.h
+++ b/net/wireless/trace.h
@@ -3030,6 +3030,25 @@ DEFINE_EVENT(wiphy_wdev_evt, rdev_abort_scan,
 	TP_PROTO(struct wiphy *wiphy, struct wireless_dev *wdev),
 	TP_ARGS(wiphy, wdev)
 );
+
+TRACE_EVENT(rdev_set_multicast_to_unicast,
+	TP_PROTO(struct wiphy *wiphy, struct net_device *netdev,
+		 const bool enabled),
+	TP_ARGS(wiphy, netdev, enabled),
+	TP_STRUCT__entry(
+		WIPHY_ENTRY
+		NETDEV_ENTRY
+		__field(bool, enabled)
+	),
+	TP_fast_assign(
+		WIPHY_ASSIGN;
+		NETDEV_ASSIGN;
+		__entry->enabled = enabled;
+	),
+	TP_printk(WIPHY_PR_FMT ", " NETDEV_PR_FMT ", unicast: %s",
+		  WIPHY_PR_ARG, NETDEV_PR_ARG,
+		  BOOL_TO_STR(__entry->enabled))
+);
 #endif /* !__RDEV_OPS_TRACE || TRACE_HEADER_MULTI_READ */
 
 #undef TRACE_INCLUDE_PATH