| Message ID | 20240212191844.1055186-2-tobias@waldekranz.com (mailing list archive) |
|---|---|
| State | Superseded |
| Delegated to: | Netdev Maintainers |
| Headers | show |
| Series | net: bridge: switchdev: Ensure MDB events are delivered exactly once | expand |
On Mon, Feb 12, 2024 at 08:18:43PM +0100, Tobias Waldekranz wrote: > 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@waldekranz.com> > --- Excellent from my side, thank you! Reviewed-by: Vladimir Oltean <olteanv@gmail.com> > @@ -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 exists, which is equivalent > + * to the action @nt of an object @obj. nitpick: replace "is exists" with something else like "is pending" or "exists". Also "action of an object" or "on an object"? > + * > + * rtnl_lock must be held. > + */
On ons, feb 14, 2024 at 18:45, Vladimir Oltean <olteanv@gmail.com> wrote: > On Mon, Feb 12, 2024 at 08:18:43PM +0100, Tobias Waldekranz wrote: >> 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@waldekranz.com> >> --- > > Excellent from my side, thank you! Thanks! > Reviewed-by: Vladimir Oltean <olteanv@gmail.com> > >> @@ -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 exists, which is equivalent >> + * to the action @nt of an object @obj. > > nitpick: replace "is exists" with something else like "is pending" or > "exists". > > Also "action of an object" or "on an object"? Yes, these are annoying. I might as well send a v5. pw-bot: changes-requested >> + * >> + * rtnl_lock must be held. >> + */
diff --git a/include/net/switchdev.h b/include/net/switchdev.h index a43062d4c734..8346b0d29542 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 ee84e783e1df..6a7cb01f121c 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 5b045284849e..7d11f31820df 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 exists, which is equivalent + * to the action @nt of 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);
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@waldekranz.com> --- include/net/switchdev.h | 3 ++ net/bridge/br_switchdev.c | 74 ++++++++++++++++++++++++--------------- net/switchdev/switchdev.c | 73 ++++++++++++++++++++++++++++++++++++++ 3 files changed, 122 insertions(+), 28 deletions(-)