bridge: fix seq check in br_mdb_dump()

In case of rehashing, introduce a global variable 'br_mdb_rehash_seq'
which gets increased every time when rehashing, and assign
net->dev_base_seq + br_mdb_rehash_seq to cb->seq.

In theory cb->seq could be wrapped to zero, but this is not
easy to fix, as net->dev_base_seq is not visible inside
br_mdb_rehash(). In practice, this is rare.

Cc: Herbert Xu <herbert@gondor.apana.org.au>
Cc: Stephen Hemminger <shemminger@vyatta.com>
Cc: "David S. Miller" <davem@davemloft.net>
Cc: Thomas Graf <tgraf@suug.ch>
Cc: Jesper Dangaard Brouer <brouer@redhat.com>
Signed-off-by: Cong Wang <amwang@redhat.com>
Signed-off-by: David S. Miller <davem@davemloft.net>

3 files changed, 5 insertions, 4 deletions

diff --git a/net/bridge/br_mdb.c b/net/bridge/br_mdb.c
index edc0d731f6b..ccc43a9bff8 100644
--- a/net/bridge/br_mdb.c
+++ b/net/bridge/br_mdb.c
@@ -117,10 +117,8 @@ static int br_mdb_dump(struct sk_buff *skb, struct netlink_callback *cb)
 
         rcu_read_lock();
 
-        /* TODO: in case of rehashing, we need to check
-         * consistency for dumping.
-         */
-        cb->seq = net->dev_base_seq;
+        /* In theory this could be wrapped to 0... */
+        cb->seq = net->dev_base_seq + br_mdb_rehash_seq;
 
         for_each_netdev_rcu(net, dev) {
                 if (dev->priv_flags & IFF_EBRIDGE) {
diff --git a/net/bridge/br_multicast.c b/net/bridge/br_multicast.c
index 68e375ac93b..847b98a1d5e 100644
--- a/net/bridge/br_multicast.c
+++ b/net/bridge/br_multicast.c
@@ -37,6 +37,7 @@
         rcu_dereference_protected(X, lockdep_is_held(&br->multicast_lock))
 
 static void br_multicast_start_querier(struct net_bridge *br);
+unsigned int br_mdb_rehash_seq;
 
 #if IS_ENABLED(CONFIG_IPV6)
 static inline int ipv6_is_transient_multicast(const struct in6_addr *addr)
@@ -338,6 +339,7 @@ static int br_mdb_rehash(struct net_bridge_mdb_htable __rcu **mdbp, int max,
                 return err;
         }
 
+        br_mdb_rehash_seq++;
         call_rcu_bh(&mdb->rcu, br_mdb_free);
 
 out:
diff --git a/net/bridge/br_private.h b/net/bridge/br_private.h
index ae0a6ec0a70..f95b766c7a9 100644
--- a/net/bridge/br_private.h
+++ b/net/bridge/br_private.h
@@ -411,6 +411,7 @@ extern int br_ioctl_deviceless_stub(struct net *net, unsigned int cmd, void __us
 
 /* br_multicast.c */
 #ifdef CONFIG_BRIDGE_IGMP_SNOOPING
+extern unsigned int br_mdb_rehash_seq;
 extern int br_multicast_rcv(struct net_bridge *br,
                             struct net_bridge_port *port,
                             struct sk_buff *skb);