Patch "net: bridge: switchdev: Skip MDB replays of deferred events on offload" has been added to the 6.6-stable tree

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This is a note to let you know that I've just added the patch titled

    net: bridge: switchdev: Skip MDB replays of deferred events on offload

to the 6.6-stable tree which can be found at:
    http://www.kernel.org/git/?p=linux/kernel/git/stable/stable-queue.git;a=summary

The filename of the patch is:
     net-bridge-switchdev-skip-mdb-replays-of-deferred-ev.patch
and it can be found in the queue-6.6 subdirectory.

If you, or anyone else, feels it should not be added to the stable tree,
please let <stable@xxxxxxxxxxxxxxx> know about it.



commit 5396f11d2bae0bb52e9cd984ae6d0bb25bd4bb60
Author: Tobias Waldekranz <tobias@xxxxxxxxxxxxxx>
Date:   Wed Feb 14 22:40:03 2024 +0100

    net: bridge: switchdev: Skip MDB replays of deferred events on offload
    
    [ Upstream commit dc489f86257cab5056e747344f17a164f63bff4b ]
    
    Before this change, generation of the list of MDB events to replay
    would race against the creation of new group memberships, either from
    the IGMP/MLD snooping logic or from user configuration.
    
    While new memberships are immediately visible to walkers of
    br->mdb_list, the notification of their existence to switchdev event
    subscribers is deferred until a later point in time. So if a replay
    list was generated during a time that overlapped with such a window,
    it would also contain a replay of the not-yet-delivered event.
    
    The driver would thus receive two copies of what the bridge internally
    considered to be one single event. On destruction of the bridge, only
    a single membership deletion event was therefore sent. As a
    consequence of this, drivers which reference count memberships (at
    least DSA), would be left with orphan groups in their hardware
    database when the bridge was destroyed.
    
    This is only an issue when replaying additions. While deletion events
    may still be pending on the deferred queue, they will already have
    been removed from br->mdb_list, so no duplicates can be generated in
    that scenario.
    
    To a user this meant that old group memberships, from a bridge in
    which a port was previously attached, could be reanimated (in
    hardware) when the port joined a new bridge, without the new bridge's
    knowledge.
    
    For example, on an mv88e6xxx system, create a snooping bridge and
    immediately add a port to it:
    
        root@infix-06-0b-00:~$ ip link add dev br0 up type bridge mcast_snooping 1 && \
        > ip link set dev x3 up master br0
    
    And then destroy the bridge:
    
        root@infix-06-0b-00:~$ ip link del dev br0
        root@infix-06-0b-00:~$ mvls atu
        ADDRESS             FID  STATE      Q  F  0  1  2  3  4  5  6  7  8  9  a
        DEV:0 Marvell 88E6393X
        33:33:00:00:00:6a     1  static     -  -  0  .  .  .  .  .  .  .  .  .  .
        33:33:ff:87:e4:3f     1  static     -  -  0  .  .  .  .  .  .  .  .  .  .
        ff:ff:ff:ff:ff:ff     1  static     -  -  0  1  2  3  4  5  6  7  8  9  a
        root@infix-06-0b-00:~$
    
    The two IPv6 groups remain in the hardware database because the
    port (x3) is notified of the host's membership twice: once via the
    original event and once via a replay. Since only a single delete
    notification is sent, the count remains at 1 when the bridge is
    destroyed.
    
    Then add the same port (or another port belonging to the same hardware
    domain) to a new bridge, this time with snooping disabled:
    
        root@infix-06-0b-00:~$ ip link add dev br1 up type bridge mcast_snooping 0 && \
        > ip link set dev x3 up master br1
    
    All multicast, including the two IPv6 groups from br0, should now be
    flooded, according to the policy of br1. But instead the old
    memberships are still active in the hardware database, causing the
    switch to only forward traffic to those groups towards the CPU (port
    0).
    
    Eliminate the race in two steps:
    
    1. Grab the write-side lock of the MDB while generating the replay
       list.
    
    This prevents new memberships from showing up while we are generating
    the replay list. But it leaves the scenario in which a deferred event
    was already generated, but not delivered, before we grabbed the
    lock. Therefore:
    
    2. Make sure that no deferred version of a replay event is already
       enqueued to the switchdev deferred queue, before adding it to the
       replay list, when replaying additions.
    
    Fixes: 4f2673b3a2b6 ("net: bridge: add helper to replay port and host-joined mdb entries")
    Signed-off-by: Tobias Waldekranz <tobias@xxxxxxxxxxxxxx>
    Reviewed-by: Vladimir Oltean <olteanv@xxxxxxxxx>
    Signed-off-by: David S. Miller <davem@xxxxxxxxxxxxx>
    Signed-off-by: Sasha Levin <sashal@xxxxxxxxxx>

diff --git a/include/net/switchdev.h b/include/net/switchdev.h
index a43062d4c734b..8346b0d29542c 100644
--- a/include/net/switchdev.h
+++ b/include/net/switchdev.h
@@ -308,6 +308,9 @@ void switchdev_deferred_process(void);
 int switchdev_port_attr_set(struct net_device *dev,
 			    const struct switchdev_attr *attr,
 			    struct netlink_ext_ack *extack);
+bool switchdev_port_obj_act_is_deferred(struct net_device *dev,
+					enum switchdev_notifier_type nt,
+					const struct switchdev_obj *obj);
 int switchdev_port_obj_add(struct net_device *dev,
 			   const struct switchdev_obj *obj,
 			   struct netlink_ext_ack *extack);
diff --git a/net/bridge/br_switchdev.c b/net/bridge/br_switchdev.c
index ee84e783e1dff..6a7cb01f121c7 100644
--- a/net/bridge/br_switchdev.c
+++ b/net/bridge/br_switchdev.c
@@ -595,21 +595,40 @@ br_switchdev_mdb_replay_one(struct notifier_block *nb, struct net_device *dev,
 }
 
 static int br_switchdev_mdb_queue_one(struct list_head *mdb_list,
+				      struct net_device *dev,
+				      unsigned long action,
 				      enum switchdev_obj_id id,
 				      const struct net_bridge_mdb_entry *mp,
 				      struct net_device *orig_dev)
 {
-	struct switchdev_obj_port_mdb *mdb;
+	struct switchdev_obj_port_mdb mdb = {
+		.obj = {
+			.id = id,
+			.orig_dev = orig_dev,
+		},
+	};
+	struct switchdev_obj_port_mdb *pmdb;
 
-	mdb = kzalloc(sizeof(*mdb), GFP_ATOMIC);
-	if (!mdb)
-		return -ENOMEM;
+	br_switchdev_mdb_populate(&mdb, mp);
 
-	mdb->obj.id = id;
-	mdb->obj.orig_dev = orig_dev;
-	br_switchdev_mdb_populate(mdb, mp);
-	list_add_tail(&mdb->obj.list, mdb_list);
+	if (action == SWITCHDEV_PORT_OBJ_ADD &&
+	    switchdev_port_obj_act_is_deferred(dev, action, &mdb.obj)) {
+		/* This event is already in the deferred queue of
+		 * events, so this replay must be elided, lest the
+		 * driver receives duplicate events for it. This can
+		 * only happen when replaying additions, since
+		 * modifications are always immediately visible in
+		 * br->mdb_list, whereas actual event delivery may be
+		 * delayed.
+		 */
+		return 0;
+	}
+
+	pmdb = kmemdup(&mdb, sizeof(mdb), GFP_ATOMIC);
+	if (!pmdb)
+		return -ENOMEM;
 
+	list_add_tail(&pmdb->obj.list, mdb_list);
 	return 0;
 }
 
@@ -677,51 +696,50 @@ br_switchdev_mdb_replay(struct net_device *br_dev, struct net_device *dev,
 	if (!br_opt_get(br, BROPT_MULTICAST_ENABLED))
 		return 0;
 
-	/* We cannot walk over br->mdb_list protected just by the rtnl_mutex,
-	 * because the write-side protection is br->multicast_lock. But we
-	 * need to emulate the [ blocking ] calling context of a regular
-	 * switchdev event, so since both br->multicast_lock and RCU read side
-	 * critical sections are atomic, we have no choice but to pick the RCU
-	 * read side lock, queue up all our events, leave the critical section
-	 * and notify switchdev from blocking context.
+	if (adding)
+		action = SWITCHDEV_PORT_OBJ_ADD;
+	else
+		action = SWITCHDEV_PORT_OBJ_DEL;
+
+	/* br_switchdev_mdb_queue_one() will take care to not queue a
+	 * replay of an event that is already pending in the switchdev
+	 * deferred queue. In order to safely determine that, there
+	 * must be no new deferred MDB notifications enqueued for the
+	 * duration of the MDB scan. Therefore, grab the write-side
+	 * lock to avoid racing with any concurrent IGMP/MLD snooping.
 	 */
-	rcu_read_lock();
+	spin_lock_bh(&br->multicast_lock);
 
-	hlist_for_each_entry_rcu(mp, &br->mdb_list, mdb_node) {
+	hlist_for_each_entry(mp, &br->mdb_list, mdb_node) {
 		struct net_bridge_port_group __rcu * const *pp;
 		const struct net_bridge_port_group *p;
 
 		if (mp->host_joined) {
-			err = br_switchdev_mdb_queue_one(&mdb_list,
+			err = br_switchdev_mdb_queue_one(&mdb_list, dev, action,
 							 SWITCHDEV_OBJ_ID_HOST_MDB,
 							 mp, br_dev);
 			if (err) {
-				rcu_read_unlock();
+				spin_unlock_bh(&br->multicast_lock);
 				goto out_free_mdb;
 			}
 		}
 
-		for (pp = &mp->ports; (p = rcu_dereference(*pp)) != NULL;
+		for (pp = &mp->ports; (p = mlock_dereference(*pp, br)) != NULL;
 		     pp = &p->next) {
 			if (p->key.port->dev != dev)
 				continue;
 
-			err = br_switchdev_mdb_queue_one(&mdb_list,
+			err = br_switchdev_mdb_queue_one(&mdb_list, dev, action,
 							 SWITCHDEV_OBJ_ID_PORT_MDB,
 							 mp, dev);
 			if (err) {
-				rcu_read_unlock();
+				spin_unlock_bh(&br->multicast_lock);
 				goto out_free_mdb;
 			}
 		}
 	}
 
-	rcu_read_unlock();
-
-	if (adding)
-		action = SWITCHDEV_PORT_OBJ_ADD;
-	else
-		action = SWITCHDEV_PORT_OBJ_DEL;
+	spin_unlock_bh(&br->multicast_lock);
 
 	list_for_each_entry(obj, &mdb_list, list) {
 		err = br_switchdev_mdb_replay_one(nb, dev,
diff --git a/net/switchdev/switchdev.c b/net/switchdev/switchdev.c
index 5b045284849e0..c9189a970eec3 100644
--- a/net/switchdev/switchdev.c
+++ b/net/switchdev/switchdev.c
@@ -19,6 +19,35 @@
 #include <linux/rtnetlink.h>
 #include <net/switchdev.h>
 
+static bool switchdev_obj_eq(const struct switchdev_obj *a,
+			     const struct switchdev_obj *b)
+{
+	const struct switchdev_obj_port_vlan *va, *vb;
+	const struct switchdev_obj_port_mdb *ma, *mb;
+
+	if (a->id != b->id || a->orig_dev != b->orig_dev)
+		return false;
+
+	switch (a->id) {
+	case SWITCHDEV_OBJ_ID_PORT_VLAN:
+		va = SWITCHDEV_OBJ_PORT_VLAN(a);
+		vb = SWITCHDEV_OBJ_PORT_VLAN(b);
+		return va->flags == vb->flags &&
+			va->vid == vb->vid &&
+			va->changed == vb->changed;
+	case SWITCHDEV_OBJ_ID_PORT_MDB:
+	case SWITCHDEV_OBJ_ID_HOST_MDB:
+		ma = SWITCHDEV_OBJ_PORT_MDB(a);
+		mb = SWITCHDEV_OBJ_PORT_MDB(b);
+		return ma->vid == mb->vid &&
+			ether_addr_equal(ma->addr, mb->addr);
+	default:
+		break;
+	}
+
+	BUG();
+}
+
 static LIST_HEAD(deferred);
 static DEFINE_SPINLOCK(deferred_lock);
 
@@ -307,6 +336,50 @@ int switchdev_port_obj_del(struct net_device *dev,
 }
 EXPORT_SYMBOL_GPL(switchdev_port_obj_del);
 
+/**
+ *	switchdev_port_obj_act_is_deferred - Is object action pending?
+ *
+ *	@dev: port device
+ *	@nt: type of action; add or delete
+ *	@obj: object to test
+ *
+ *	Returns true if a deferred item is pending, which is
+ *	equivalent to the action @nt on an object @obj.
+ *
+ *	rtnl_lock must be held.
+ */
+bool switchdev_port_obj_act_is_deferred(struct net_device *dev,
+					enum switchdev_notifier_type nt,
+					const struct switchdev_obj *obj)
+{
+	struct switchdev_deferred_item *dfitem;
+	bool found = false;
+
+	ASSERT_RTNL();
+
+	spin_lock_bh(&deferred_lock);
+
+	list_for_each_entry(dfitem, &deferred, list) {
+		if (dfitem->dev != dev)
+			continue;
+
+		if ((dfitem->func == switchdev_port_obj_add_deferred &&
+		     nt == SWITCHDEV_PORT_OBJ_ADD) ||
+		    (dfitem->func == switchdev_port_obj_del_deferred &&
+		     nt == SWITCHDEV_PORT_OBJ_DEL)) {
+			if (switchdev_obj_eq((const void *)dfitem->data, obj)) {
+				found = true;
+				break;
+			}
+		}
+	}
+
+	spin_unlock_bh(&deferred_lock);
+
+	return found;
+}
+EXPORT_SYMBOL_GPL(switchdev_port_obj_act_is_deferred);
+
 static ATOMIC_NOTIFIER_HEAD(switchdev_notif_chain);
 static BLOCKING_NOTIFIER_HEAD(switchdev_blocking_notif_chain);
 




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