net: dsa: fix db type confusion in host fdb/mdb add/del

We have the following code paths:

Host FDB (unicast RX filtering):

dsa_port_standalone_host_fdb_add()   dsa_port_bridge_host_fdb_add()
               |                                     |
               +--------------+         +------------+
                              |         |
                              v         v
                         dsa_port_host_fdb_add()

dsa_port_standalone_host_fdb_del()   dsa_port_bridge_host_fdb_del()
               |                                     |
               +--------------+         +------------+
                              |         |
                              v         v
                         dsa_port_host_fdb_del()

Host MDB (multicast RX filtering):

dsa_port_standalone_host_mdb_add()   dsa_port_bridge_host_mdb_add()
               |                                     |
               +--------------+         +------------+
                              |         |
                              v         v
                         dsa_port_host_mdb_add()

dsa_port_standalone_host_mdb_del()   dsa_port_bridge_host_mdb_del()
               |                                     |
               +--------------+         +------------+
                              |         |
                              v         v
                         dsa_port_host_mdb_del()

The logic added by commit 5e8a1e03 ("net: dsa: install secondary
unicast and multicast addresses as host FDB/MDB") zeroes out
db.bridge.num if the switch doesn't support ds->fdb_isolation
(the majority doesn't). This is done for a reason explained in commit
c2693363 ("net: dsa: request drivers to perform FDB isolation").

Taking a single code path as example - dsa_port_host_fdb_add() - the
others are similar - the problem is that this function handles:
- DSA_DB_PORT databases, when called from
  dsa_port_standalone_host_fdb_add()
- DSA_DB_BRIDGE databases, when called from
  dsa_port_bridge_host_fdb_add()

So, if dsa_port_host_fdb_add() were to make any change on the
"bridge.num" attribute of the database, this would only be correct for a
DSA_DB_BRIDGE, and a type confusion for a DSA_DB_PORT bridge.

However, this bug is without consequences, for 2 reasons:

- dsa_port_standalone_host_fdb_add() is only called from code which is
  (in)directly guarded by dsa_switch_supports_uc_filtering(ds), and that
  function only returns true if ds->fdb_isolation is set. So, the code
  only executed for DSA_DB_BRIDGE databases.

- Even if the code was not dead for DSA_DB_PORT, we have the following
  memory layout:

struct dsa_bridge {
	struct net_device *dev;
	unsigned int num;
	bool tx_fwd_offload;
	refcount_t refcount;
};

struct dsa_db {
	enum dsa_db_type type;

	union {
		const struct dsa_port *dp; // DSA_DB_PORT
		struct dsa_lag lag;
		struct dsa_bridge bridge; // DSA_DB_BRIDGE
	};
};

So, the zeroization of dsa_db :: bridge :: num on a dsa_db structure of
type DSA_DB_PORT would access memory which is unused, because we only
use dsa_db :: dp for DSA_DB_PORT, and this is mapped at the same address
with dsa_db :: dev for DSA_DB_BRIDGE, thanks to the union definition.

It is correct to fix up dsa_db :: bridge :: num only from code paths
that come from the bridge / switchdev, so move these there.
Signed-off-by: Vladimir Oltean <vladimir.oltean@nxp.com>
Reviewed-by: Simon Horman <simon.horman@corigine.com>
Reviewed-by: Florian Fainelli <f.fainelli@gmail.com>
Link: https://lore.kernel.org/r/20230329133819.697642-1-vladimir.oltean@nxp.comSigned-off-by: Jakub Kicinski <kuba@kernel.org>

net/dsa/port.c

@@ -1028,9 +1028,6 @@ static int dsa_port_host_fdb_add(struct dsa_port *dp,
 		.db = db,
 	};
 
-	if (!dp->ds->fdb_isolation)
-		info.db.bridge.num = 0;
-
 	return dsa_port_notify(dp, DSA_NOTIFIER_HOST_FDB_ADD, &info);
 }
 
@@ -1055,6 +1052,9 @@ int dsa_port_bridge_host_fdb_add(struct dsa_port *dp,
 	};
 	int err;
 
+	if (!dp->ds->fdb_isolation)
+		db.bridge.num = 0;
+
 	/* Avoid a call to __dev_set_promiscuity() on the master, which
 	 * requires rtnl_lock(), since we can't guarantee that is held here,
 	 * and we can't take it either.
@@ -1079,9 +1079,6 @@ static int dsa_port_host_fdb_del(struct dsa_port *dp,
 		.db = db,
 	};
 
-	if (!dp->ds->fdb_isolation)
-		info.db.bridge.num = 0;
-
 	return dsa_port_notify(dp, DSA_NOTIFIER_HOST_FDB_DEL, &info);
 }
 
@@ -1106,6 +1103,9 @@ int dsa_port_bridge_host_fdb_del(struct dsa_port *dp,
 	};
 	int err;
 
+	if (!dp->ds->fdb_isolation)
+		db.bridge.num = 0;
+
 	if (master->priv_flags & IFF_UNICAST_FLT) {
 		err = dev_uc_del(master, addr);
 		if (err)
@@ -1210,9 +1210,6 @@ static int dsa_port_host_mdb_add(const struct dsa_port *dp,
 		.db = db,
 	};
 
-	if (!dp->ds->fdb_isolation)
-		info.db.bridge.num = 0;
-
 	return dsa_port_notify(dp, DSA_NOTIFIER_HOST_MDB_ADD, &info);
 }
 
@@ -1237,6 +1234,9 @@ int dsa_port_bridge_host_mdb_add(const struct dsa_port *dp,
 	};
 	int err;
 
+	if (!dp->ds->fdb_isolation)
+		db.bridge.num = 0;
+
 	err = dev_mc_add(master, mdb->addr);
 	if (err)
 		return err;
@@ -1254,9 +1254,6 @@ static int dsa_port_host_mdb_del(const struct dsa_port *dp,
 		.db = db,
 	};
 
-	if (!dp->ds->fdb_isolation)
-		info.db.bridge.num = 0;
-
 	return dsa_port_notify(dp, DSA_NOTIFIER_HOST_MDB_DEL, &info);
 }
 
@@ -1281,6 +1278,9 @@ int dsa_port_bridge_host_mdb_del(const struct dsa_port *dp,
 	};
 	int err;
 
+	if (!dp->ds->fdb_isolation)
+		db.bridge.num = 0;
+
 	err = dev_mc_del(master, mdb->addr);
 	if (err)
 		return err;