Commit 99e79b67 authored by Jakub Kicinski's avatar Jakub Kicinski
Browse files

Merge branch 'bridge-add-a-limit-on-learned-fdb-entries' 

Johannes Nixdorf says:

====================
bridge: Add a limit on learned FDB entries

Introduce a limit on the amount of learned FDB entries on a bridge,
configured by netlink with a build time default on bridge creation in
the kernel config.

For backwards compatibility the kernel config default is disabling the
limit (0).

Without any limit a malicious actor may OOM a kernel by spamming packets
with changing MAC addresses on their bridge port, so allow the bridge
creator to limit the number of entries.

Currently the manual entries are identified by the bridge flags
BR_FDB_LOCAL or BR_FDB_ADDED_BY_USER, atomically bundled under the new
flag BR_FDB_DYNAMIC_LEARNED. This means the limit also applies to
entries created with BR_FDB_ADDED_BY_EXT_LEARN but none of BR_FDB_LOCAL
or BR_FDB_ADDED_BY_USER, e.g. ones added by SWITCHDEV_FDB_ADD_TO_BRIDGE.

Link to the corresponding iproute2 changes:
https://lore.kernel.org/r/20230919-fdb_limit-v4-1-b4d2dc4df30f@avm.de

v4: https://lore.kernel.org/r/20230919-fdb_limit-v4-0-39f0293807b8@avm.de/
v3: https://lore.kernel.org/r/20230905-fdb_limit-v3-0-7597cd500a82@avm.de/
v2: https://lore.kernel.org/netdev/20230619071444.14625-1-jnixdorf-oss@avm.de/
v1: https://lore.kernel.org/netdev/20230515085046.4457-1-jnixdorf-oss@avm.de/
====================

Link: https://lore.kernel.org/r/20231016-fdb_limit-v5-0-32cddff87758@avm.de


Signed-off-by: default avatarJakub Kicinski <kuba@kernel.org>
parents 56a7bb12 6f840903

include/uapi/linux/if_link.h

+2 −0
Original line number Diff line number Diff line
@@ -510,6 +510,8 @@ enum { 
	IFLA_BR_VLAN_STATS_PER_PORT,

	IFLA_BR_MULTI_BOOLOPT,

	IFLA_BR_MCAST_QUERIER_STATE,

	IFLA_BR_FDB_N_LEARNED,

	IFLA_BR_FDB_MAX_LEARNED,

	__IFLA_BR_MAX,

};

net/bridge/br_fdb.c

+37 −5
Original line number Diff line number Diff line
@@ -329,11 +329,18 @@ static void fdb_delete(struct net_bridge *br, struct net_bridge_fdb_entry *f, 
	hlist_del_init_rcu(&f->fdb_node);

	rhashtable_remove_fast(&br->fdb_hash_tbl, &f->rhnode,

			       br_fdb_rht_params);

	if (test_and_clear_bit(BR_FDB_DYNAMIC_LEARNED, &f->flags))

		atomic_dec(&br->fdb_n_learned);

	fdb_notify(br, f, RTM_DELNEIGH, swdev_notify);

	call_rcu(&f->rcu, fdb_rcu_free);

}



/* Delete a local entry if no other port had the same address. */

/* Delete a local entry if no other port had the same address.

 *

 * This function should only be called on entries with BR_FDB_LOCAL set,

 * so even with BR_FDB_ADDED_BY_USER cleared we never need to increase

 * the accounting for dynamically learned entries again.

 */

static void fdb_delete_local(struct net_bridge *br,

			     const struct net_bridge_port *p,

			     struct net_bridge_fdb_entry *f)
@@ -388,9 +395,20 @@ static struct net_bridge_fdb_entry *fdb_create(struct net_bridge *br, 
					       __u16 vid,

					       unsigned long flags)

{

	bool learned = !test_bit(BR_FDB_ADDED_BY_USER, &flags) &&

		       !test_bit(BR_FDB_LOCAL, &flags);

	u32 max_learned = READ_ONCE(br->fdb_max_learned);

	struct net_bridge_fdb_entry *fdb;

	int err;



	if (likely(learned)) {

		int n_learned = atomic_read(&br->fdb_n_learned);



		if (unlikely(max_learned && n_learned >= max_learned))

			return NULL;

		__set_bit(BR_FDB_DYNAMIC_LEARNED, &flags);

	}



	fdb = kmem_cache_alloc(br_fdb_cache, GFP_ATOMIC);

	if (!fdb)

		return NULL;
@@ -407,6 +425,9 @@ static struct net_bridge_fdb_entry *fdb_create(struct net_bridge *br, 
		return NULL;

	}



	if (likely(learned))

		atomic_inc(&br->fdb_n_learned);



	hlist_add_head_rcu(&fdb->fdb_node, &br->fdb_list);



	return fdb;
@@ -912,8 +933,12 @@ void br_fdb_update(struct net_bridge *br, struct net_bridge_port *source, 
					clear_bit(BR_FDB_LOCKED, &fdb->flags);

			}



			if (unlikely(test_bit(BR_FDB_ADDED_BY_USER, &flags)))

			if (unlikely(test_bit(BR_FDB_ADDED_BY_USER, &flags))) {

				set_bit(BR_FDB_ADDED_BY_USER, &fdb->flags);

				if (test_and_clear_bit(BR_FDB_DYNAMIC_LEARNED,

						       &fdb->flags))

					atomic_dec(&br->fdb_n_learned);

			}

			if (unlikely(fdb_modified)) {

				trace_br_fdb_update(br, source, addr, vid, flags);

				fdb_notify(br, fdb, RTM_NEWNEIGH, true);
@@ -1075,7 +1100,8 @@ static int fdb_add_entry(struct net_bridge *br, struct net_bridge_port *source, 
		if (!(flags & NLM_F_CREATE))

			return -ENOENT;



		fdb = fdb_create(br, source, addr, vid, 0);

		fdb = fdb_create(br, source, addr, vid,

				 BIT(BR_FDB_ADDED_BY_USER));

		if (!fdb)

			return -ENOMEM;
@@ -1088,6 +1114,10 @@ static int fdb_add_entry(struct net_bridge *br, struct net_bridge_port *source, 
			WRITE_ONCE(fdb->dst, source);

			modified = true;

		}



		set_bit(BR_FDB_ADDED_BY_USER, &fdb->flags);

		if (test_and_clear_bit(BR_FDB_DYNAMIC_LEARNED, &fdb->flags))

			atomic_dec(&br->fdb_n_learned);

	}



	if (fdb_to_nud(br, fdb) != state) {
@@ -1119,8 +1149,6 @@ static int fdb_add_entry(struct net_bridge *br, struct net_bridge_port *source, 
	if (fdb_handle_notify(fdb, notify))

		modified = true;



	set_bit(BR_FDB_ADDED_BY_USER, &fdb->flags);



	fdb->used = jiffies;

	if (modified) {

		if (refresh)
@@ -1464,6 +1492,10 @@ int br_fdb_external_learn_add(struct net_bridge *br, struct net_bridge_port *p, 
		if (!p)

			set_bit(BR_FDB_LOCAL, &fdb->flags);



		if ((swdev_notify || !p) &&

		    test_and_clear_bit(BR_FDB_DYNAMIC_LEARNED, &fdb->flags))

			atomic_dec(&br->fdb_n_learned);



		if (modified)

			fdb_notify(br, fdb, RTM_NEWNEIGH, swdev_notify);

	}

net/bridge/br_netlink.c

+16 −1
Original line number Diff line number Diff line
@@ -1229,6 +1229,8 @@ static size_t br_port_get_slave_size(const struct net_device *brdev, 
}



static const struct nla_policy br_policy[IFLA_BR_MAX + 1] = {

	[IFLA_BR_UNSPEC]	= { .strict_start_type =

				    IFLA_BR_FDB_N_LEARNED },

	[IFLA_BR_FORWARD_DELAY]	= { .type = NLA_U32 },

	[IFLA_BR_HELLO_TIME]	= { .type = NLA_U32 },

	[IFLA_BR_MAX_AGE]	= { .type = NLA_U32 },
@@ -1265,6 +1267,8 @@ static const struct nla_policy br_policy[IFLA_BR_MAX + 1] = { 
	[IFLA_BR_VLAN_STATS_PER_PORT] = { .type = NLA_U8 },

	[IFLA_BR_MULTI_BOOLOPT] =

		NLA_POLICY_EXACT_LEN(sizeof(struct br_boolopt_multi)),

	[IFLA_BR_FDB_N_LEARNED] = { .type = NLA_REJECT },

	[IFLA_BR_FDB_MAX_LEARNED] = { .type = NLA_U32 },

};



static int br_changelink(struct net_device *brdev, struct nlattr *tb[],
@@ -1539,6 +1543,12 @@ static int br_changelink(struct net_device *brdev, struct nlattr *tb[], 
			return err;

	}



	if (data[IFLA_BR_FDB_MAX_LEARNED]) {

		u32 val = nla_get_u32(data[IFLA_BR_FDB_MAX_LEARNED]);



		WRITE_ONCE(br->fdb_max_learned, val);

	}



	return 0;

}
@@ -1593,6 +1603,8 @@ static size_t br_get_size(const struct net_device *brdev) 
	       nla_total_size_64bit(sizeof(u64)) + /* IFLA_BR_TOPOLOGY_CHANGE_TIMER */

	       nla_total_size_64bit(sizeof(u64)) + /* IFLA_BR_GC_TIMER */

	       nla_total_size(ETH_ALEN) +       /* IFLA_BR_GROUP_ADDR */

	       nla_total_size(sizeof(u32)) +    /* IFLA_BR_FDB_N_LEARNED */

	       nla_total_size(sizeof(u32)) +    /* IFLA_BR_FDB_MAX_LEARNED */

#ifdef CONFIG_BRIDGE_IGMP_SNOOPING

	       nla_total_size(sizeof(u8)) +     /* IFLA_BR_MCAST_ROUTER */

	       nla_total_size(sizeof(u8)) +     /* IFLA_BR_MCAST_SNOOPING */
@@ -1668,7 +1680,10 @@ static int br_fill_info(struct sk_buff *skb, const struct net_device *brdev) 
	    nla_put_u8(skb, IFLA_BR_TOPOLOGY_CHANGE_DETECTED,

		       br->topology_change_detected) ||

	    nla_put(skb, IFLA_BR_GROUP_ADDR, ETH_ALEN, br->group_addr) ||

	    nla_put(skb, IFLA_BR_MULTI_BOOLOPT, sizeof(bm), &bm))

	    nla_put(skb, IFLA_BR_MULTI_BOOLOPT, sizeof(bm), &bm) ||

	    nla_put_u32(skb, IFLA_BR_FDB_N_LEARNED,

			atomic_read(&br->fdb_n_learned)) ||

	    nla_put_u32(skb, IFLA_BR_FDB_MAX_LEARNED, br->fdb_max_learned))

		return -EMSGSIZE;



#ifdef CONFIG_BRIDGE_VLAN_FILTERING

net/bridge/br_private.h

+4 −0
Original line number Diff line number Diff line
@@ -274,6 +274,7 @@ enum { 
	BR_FDB_NOTIFY,

	BR_FDB_NOTIFY_INACTIVE,

	BR_FDB_LOCKED,

	BR_FDB_DYNAMIC_LEARNED,

};



struct net_bridge_fdb_key {
@@ -555,6 +556,9 @@ struct net_bridge { 
	struct kobject			*ifobj;

	u32				auto_cnt;



	atomic_t			fdb_n_learned;

	u32				fdb_max_learned;



#ifdef CONFIG_NET_SWITCHDEV

	/* Counter used to make sure that hardware domains get unique

	 * identifiers in case a bridge spans multiple switchdev instances.

tools/testing/selftests/net/forwarding/Makefile

+2 −1
Original line number Diff line number Diff line 
# SPDX-License-Identifier: GPL-2.0+ OR MIT



TEST_PROGS = bridge_igmp.sh \

TEST_PROGS = bridge_fdb_learning_limit.sh \

	bridge_igmp.sh \

	bridge_locked_port.sh \

	bridge_mdb.sh \

	bridge_mdb_host.sh \