4 files changed, 25 insertions, 33 deletions

diff --git a/net/bridge/br.c b/net/bridge/br.c
index 26e1616b2c90..671d13c10f6f 100644
--- a/net/bridge/br.c
+++ b/net/bridge/br.c
@@ -52,7 +52,7 @@ static int br_device_event(struct notifier_block *unused, unsigned long event, v
 
 	switch (event) {
 	case NETDEV_CHANGEMTU:
-		dev_set_mtu(br->dev, br_mtu(br));
+		br_mtu_auto_adjust(br);
 		break;
 
 	case NETDEV_CHANGEADDR:
diff --git a/net/bridge/br_device.c b/net/bridge/br_device.c
index 278fc999d355..e682a668ce57 100644
--- a/net/bridge/br_device.c
+++ b/net/bridge/br_device.c
@@ -224,11 +224,11 @@ static void br_get_stats64(struct net_device *dev,
 static int br_change_mtu(struct net_device *dev, int new_mtu)
 {
 	struct net_bridge *br = netdev_priv(dev);
-	if (new_mtu > br_mtu(br))
-		return -EINVAL;
 
 	dev->mtu = new_mtu;
 
+	/* this flag will be cleared if the MTU was automatically adjusted */
+	br->mtu_set_by_user = true;
 #if IS_ENABLED(CONFIG_BRIDGE_NETFILTER)
 	/* remember the MTU in the rtable for PMTU */
 	dst_metric_set(&br->fake_rtable.dst, RTAX_MTU, new_mtu);
diff --git a/net/bridge/br_if.c b/net/bridge/br_if.c
index 87b2afd455c7..82c1a6f430b3 100644
--- a/net/bridge/br_if.c
+++ b/net/bridge/br_if.c
@@ -424,41 +424,32 @@ int br_del_bridge(struct net *net, const char *name)
 	return ret;
 }
 
-static bool min_mtu(int a, int b)
-{
-	return a < b ? 1 : 0;
-}
-
-static bool max_mtu(int a, int b)
-{
-	return a > b ? 1 : 0;
-}
-
 /* MTU of the bridge pseudo-device: ETH_DATA_LEN or the minimum of the ports */
-static int __br_mtu(const struct net_bridge *br, bool (compare_fn)(int, int))
+static int br_mtu_min(const struct net_bridge *br)
 {
 	const struct net_bridge_port *p;
-	int mtu = 0;
+	int ret_mtu = 0;
 
-	ASSERT_RTNL();
+	list_for_each_entry(p, &br->port_list, list)
+		if (!ret_mtu || ret_mtu > p->dev->mtu)
+			ret_mtu = p->dev->mtu;
 
-	if (list_empty(&br->port_list))
-		mtu = ETH_DATA_LEN;
-	else {
-		list_for_each_entry(p, &br->port_list, list) {
-			if (!mtu || compare_fn(p->dev->mtu, mtu))
-				mtu = p->dev->mtu;
-		}
-	}
-	return mtu;
+	return ret_mtu ? ret_mtu : ETH_DATA_LEN;
 }
 
-int br_mtu(const struct net_bridge *br)
+void br_mtu_auto_adjust(struct net_bridge *br)
 {
-	if (br_vlan_enabled(br->dev))
-		return __br_mtu(br, max_mtu);
-	else
-		return __br_mtu(br, min_mtu);
+	ASSERT_RTNL();
+
+	/* if the bridge MTU was manually configured don't mess with it */
+	if (br->mtu_set_by_user)
+		return;
+
+	/* change to the minimum MTU and clear the flag which was set by
+	 * the bridge ndo_change_mtu callback
+	 */
+	dev_set_mtu(br->dev, br_mtu_min(br));
+	br->mtu_set_by_user = false;
 }
 
 static void br_set_gso_limits(struct net_bridge *br)
@@ -612,7 +603,7 @@ int br_add_if(struct net_bridge *br, struct net_device *dev,
 	if (changed_addr)
 		call_netdevice_notifiers(NETDEV_CHANGEADDR, br->dev);
 
-	dev_set_mtu(br->dev, br_mtu(br));
+	br_mtu_auto_adjust(br);
 	br_set_gso_limits(br);
 
 	kobject_uevent(&p->kobj, KOBJ_ADD);
@@ -659,7 +650,7 @@ int br_del_if(struct net_bridge *br, struct net_device *dev)
 	 */
 	del_nbp(p);
 
-	dev_set_mtu(br->dev, br_mtu(br));
+	br_mtu_auto_adjust(br);
 	br_set_gso_limits(br);
 
 	spin_lock_bh(&br->lock);
diff --git a/net/bridge/br_private.h b/net/bridge/br_private.h
index 048d5b51813b..a7cb3ece5031 100644
--- a/net/bridge/br_private.h
+++ b/net/bridge/br_private.h
@@ -410,6 +410,7 @@ struct net_bridge {
 	int offload_fwd_mark;
 #endif
 	bool				neigh_suppress_enabled;
+	bool				mtu_set_by_user;
 	struct hlist_head		fdb_list;
 };
 
@@ -578,7 +579,7 @@ int br_del_bridge(struct net *net, const char *name);
 int br_add_if(struct net_bridge *br, struct net_device *dev,
 	      struct netlink_ext_ack *extack);
 int br_del_if(struct net_bridge *br, struct net_device *dev);
-int br_mtu(const struct net_bridge *br);
+void br_mtu_auto_adjust(struct net_bridge *br);
 netdev_features_t br_features_recompute(struct net_bridge *br,
 					netdev_features_t features);
 void br_port_flags_change(struct net_bridge_port *port, unsigned long mask);