Merge branch 'net-bridge-mcast-fix-mdb_n_entries-counting-warning'

Nikolay Aleksandrov says:

====================
net: bridge: mcast: fix mdb_n_entries counting warning

The first patch fixes a warning in the mdb_n_entries code which was
reported by syzbot, the second patch adds tests for different ways
which used to trigger said warning. For more information please check
the individual commit messages.
====================

Link: https://patch.msgid.link/20260213070031.1400003-1-nikolay@nvidia.com
Signed-off-by: Paolo Abeni <pabeni@redhat.com>

1 files changed, 18 insertions, 27 deletions

diff --git a/net/bridge/br_multicast.c b/net/bridge/br_multicast.c
index dccae08b4f4c..b6a5147886ca 100644
--- a/net/bridge/br_multicast.c
+++ b/net/bridge/br_multicast.c
@@ -244,14 +244,11 @@ br_multicast_port_vid_to_port_ctx(struct net_bridge_port *port, u16 vid)
 
 	lockdep_assert_held_once(&port->br->multicast_lock);
 
-	if (!br_opt_get(port->br, BROPT_MCAST_VLAN_SNOOPING_ENABLED))
-		return NULL;
-
 	/* Take RCU to access the vlan. */
 	rcu_read_lock();
 
 	vlan = br_vlan_find(nbp_vlan_group_rcu(port), vid);
-	if (vlan && !br_multicast_port_ctx_vlan_disabled(&vlan->port_mcast_ctx))
+	if (vlan)
 		pmctx = &vlan->port_mcast_ctx;
 
 	rcu_read_unlock();
@@ -701,7 +698,10 @@ br_multicast_port_ngroups_inc_one(struct net_bridge_mcast_port *pmctx,
 	u32 max = READ_ONCE(pmctx->mdb_max_entries);
 	u32 n = READ_ONCE(pmctx->mdb_n_entries);
 
-	if (max && n >= max) {
+	/* enforce the max limit when it's a port pmctx or a port-vlan pmctx
+	 * with snooping enabled
+	 */
+	if (!br_multicast_port_ctx_vlan_disabled(pmctx) && max && n >= max) {
 		NL_SET_ERR_MSG_FMT_MOD(extack, "%s is already in %u groups, and mcast_max_groups=%u",
 				       what, n, max);
 		return -E2BIG;
@@ -736,9 +736,7 @@ static int br_multicast_port_ngroups_inc(struct net_bridge_port *port,
 		return err;
 	}
 
-	/* Only count on the VLAN context if VID is given, and if snooping on
-	 * that VLAN is enabled.
-	 */
+	/* Only count on the VLAN context if VID is given */
 	if (!group->vid)
 		return 0;
 
@@ -2011,6 +2009,18 @@ void br_multicast_port_ctx_init(struct net_bridge_port *port,
 	timer_setup(&pmctx->ip6_own_query.timer,
 		    br_ip6_multicast_port_query_expired, 0);
 #endif
+	/* initialize mdb_n_entries if a new port vlan is being created */
+	if (vlan) {
+		struct net_bridge_port_group *pg;
+		u32 n = 0;
+
+		spin_lock_bh(&port->br->multicast_lock);
+		hlist_for_each_entry(pg, &port->mglist, mglist)
+			if (pg->key.addr.vid == vlan->vid)
+				n++;
+		WRITE_ONCE(pmctx->mdb_n_entries, n);
+		spin_unlock_bh(&port->br->multicast_lock);
+	}
 }
 
 void br_multicast_port_ctx_deinit(struct net_bridge_mcast_port *pmctx)
@@ -2094,25 +2104,6 @@ static void __br_multicast_enable_port_ctx(struct net_bridge_mcast_port *pmctx)
 		br_ip4_multicast_add_router(brmctx, pmctx);
 		br_ip6_multicast_add_router(brmctx, pmctx);
 	}
-
-	if (br_multicast_port_ctx_is_vlan(pmctx)) {
-		struct net_bridge_port_group *pg;
-		u32 n = 0;
-
-		/* The mcast_n_groups counter might be wrong. First,
-		 * BR_VLFLAG_MCAST_ENABLED is toggled before temporary entries
-		 * are flushed, thus mcast_n_groups after the toggle does not
-		 * reflect the true values. And second, permanent entries added
-		 * while BR_VLFLAG_MCAST_ENABLED was disabled, are not reflected
-		 * either. Thus we have to refresh the counter.
-		 */
-
-		hlist_for_each_entry(pg, &pmctx->port->mglist, mglist) {
-			if (pg->key.addr.vid == pmctx->vlan->vid)
-				n++;
-		}
-		WRITE_ONCE(pmctx->mdb_n_entries, n);
-	}
 }
 
 static void br_multicast_enable_port_ctx(struct net_bridge_mcast_port *pmctx)