Add a Kconfig option to configure a default FDB learning limit system
wide, so a distributor building a special purpose kernel can limit all
created bridges by default.

The limit is only a soft default setting and overrideable on a per bridge
basis using netlink.

Signed-off-by: Johannes Nixdorf <redacted>
---
  net/bridge/Kconfig     | 13 +++++++++++++
  net/bridge/br_device.c |  2 ++
  2 files changed, 15 insertions(+)

diff --git a/net/bridge/Kconfig b/net/bridge/Kconfig
index 3c8ded7d3e84..c0d9c08088c4 100644
--- a/net/bridge/Kconfig
+++ b/net/bridge/Kconfig

@@ -84,3 +84,16 @@ config BRIDGE_CFM
  	  Say N to exclude this support and reduce the binary size.
  
  	  If unsure, say N.
+
+config BRIDGE_DEFAULT_FDB_MAX_LEARNED
+	int "Default FDB learning limit"
+	default 0
+	depends on BRIDGE
+	help
+	  Sets a default limit on the number of learned FDB entries on
+	  new bridges. This limit can be overwritten via netlink on a
+	  per bridge basis.
+
+	  The default of 0 disables the limit.
+
+	  If unsure, say 0.

diff --git a/net/bridge/br_device.c b/net/bridge/br_device.c
index 9a5ea06236bd..3214391c15a0 100644
--- a/net/bridge/br_device.c
+++ b/net/bridge/br_device.c

@@ -531,6 +531,8 @@ void br_dev_setup(struct net_device *dev)
  	br->bridge_ageing_time = br->ageing_time = BR_DEFAULT_AGEING_TIME;
  	dev->max_mtu = ETH_MAX_MTU;
  
+	br->fdb_max_learned = CONFIG_BRIDGE_DEFAULT_FDB_MAX_LEARNED;
+
  	br_netfilter_rtable_init(br);
  	br_stp_timer_init(br);
  	br_multicast_init(br);