realtek: fix flooding of unsnoopable multicast addresses

RFC4541, section 2.1.2 says:

  Packets with a destination IP (DIP) address in the 224.0.0.X range
  which are not IGMP must be forwarded on all ports.

And section 3 says:

  In IPv6, the data forwarding rules are more straight forward because
  MLD is mandated for addresses with scope 2 (link-scope) or greater.
  The only exception is the address FF02::1 which is the all hosts
  link-scope address for which MLD messages are never sent.  Packets
  with the all hosts link-scope address should be forwarded on all
  ports.

However, currently when a listener on FF12::1 or FF12::1234:0:1 for
example joins then not only packets to these addresses but also for
FF02::1 won't be flooded to all ports anymore, too. Which violates
RFC4541.

This happens because A): They all map to the same ethernet multicast
address, that is 33:33:00:00:00:01. And B) the VLAN profile L2
unknown MC flood setting will only apply flooding of 33:33:00:00:00:01
if there is no specific listener registered for it.

So to fix this, avoid registering an MDB entry in the switch for
33:33:00:00:00:01 at all.

The downside of this is that FF12::1, FF12::1234:0:1 etc.
will always be flooded, too. However fixing the handling of 224.0.0.X
and FF02::1 and adhering to RFC4541 must have priority to avoid
undesired packetloss, to avoid breaking IPv4/IPv6.

Tested-on: ZyXEL GS1900-24HP v1

Fixes: cde31976e375 ("realtek: Add support for Layer 2 Multicast")
Signed-off-by: Linus Lüssing <[email protected]>
Link: https://github.com/openwrt/openwrt/pull/18769
Signed-off-by: Robert Marko <[email protected]>

target/linux/realtek/files-6.6/drivers/net/dsa/rtl83xx/dsa.c

@@ -7,6 +7,15 @@
 
 #include "rtl83xx.h"
 
+static const u8 ipv4_ll_mcast_addr_base[ETH_ALEN] =
+{ 0x01, 0x00, 0x5e, 0x00, 0x00, 0x00 };
+static const u8 ipv4_ll_mcast_addr_mask[ETH_ALEN] =
+{ 0xff, 0xff, 0xff, 0xff, 0xff, 0x00 };
+static const u8 ipv6_all_hosts_mcast_addr_base[ETH_ALEN] =
+{ 0x33, 0x33, 0x00, 0x00, 0x00, 0x01 };
+static const u8 ipv6_all_hosts_mcast_addr_mask[ETH_ALEN] =
+{ 0xff, 0xff, 0xff, 0xff, 0xff, 0xff };
+
 extern struct rtl83xx_soc_info soc_info;
 
 static void rtl83xx_init_stats(struct rtl838x_switch_priv *priv)
@@ -1752,6 +1761,24 @@ static int rtl83xx_port_fdb_dump(struct dsa_switch *ds, int port,
 	return 0;
 }
 
+static bool rtl83xx_mac_is_unsnoop(const unsigned char *addr)
+{
+	/*
+	 * RFC4541, section 2.1.2.2 + section 3:
+	 * Unsnoopable address ranges must always be flooded.
+	 *
+	 * mapped MAC for 224.0.0.x -> 01:00:5e:00:00:xx
+	 * mapped MAC for ff02::1 -> 33:33:00:00:00:01
+	 */
+	if (ether_addr_equal_masked(addr, ipv4_ll_mcast_addr_base,
+				    ipv4_ll_mcast_addr_mask) ||
+	    ether_addr_equal_masked(addr, ipv6_all_hosts_mcast_addr_base,
+				    ipv6_all_hosts_mcast_addr_mask))
+		return true;
+
+	return false;
+}
+
 static int rtl83xx_port_mdb_add(struct dsa_switch *ds, int port,
 				const struct switchdev_obj_port_mdb *mdb,
 				const struct dsa_db db)
@@ -1774,6 +1801,13 @@ static int rtl83xx_port_mdb_add(struct dsa_switch *ds, int port,
 		return -EINVAL;
 	}
 
+	if (rtl83xx_mac_is_unsnoop(mdb->addr)) {
+		dev_dbg(priv->dev,
+			"%s: %pM might belong to an unsnoopable IP. ignore\n",
+			__func__, mdb->addr);
+		return -EADDRNOTAVAIL;
+	}
+
 	mutex_lock(&priv->reg_mutex);
 
 	idx = rtl83xx_find_l2_hash_entry(priv, seed, false, &e);
@@ -1847,6 +1881,13 @@ int rtl83xx_port_mdb_del(struct dsa_switch *ds, int port,
 		return 0;
 	}
 
+	if (rtl83xx_mac_is_unsnoop(mdb->addr)) {
+		dev_dbg(priv->dev,
+			"%s: %pM might belong to an unsnoopable IP. ignore\n",
+			__func__, mdb->addr);
+		return 0;
+	}
+
 	mutex_lock(&priv->reg_mutex);
 
 	idx = rtl83xx_find_l2_hash_entry(priv, seed, true, &e);