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Commit 3f890923 authored by Stephen Hemminger's avatar Stephen Hemminger Committed by David S. Miller
Browse files

bridge: simpler hash with salt 



Instead of hashing the whole Ethernet address, it should be faster
to just use the last 4 bytes. Add a random salt value to the hash
to make it more difficult to construct worst case DoS hash chains.

Signed-off-by: default avatarStephen Hemminger <shemminger@linux-foundation.org>
parent 467aea0d

net/bridge/br_fdb.c

+12 −5
Original line number Diff line number Diff line
@@ -20,19 +20,24 @@ 
#include <linux/netdevice.h>

#include <linux/etherdevice.h>

#include <linux/jhash.h>

#include <linux/random.h>

#include <asm/atomic.h>

#include <asm/unaligned.h>

#include "br_private.h"



static struct kmem_cache *br_fdb_cache __read_mostly;

static int fdb_insert(struct net_bridge *br, struct net_bridge_port *source,

		      const unsigned char *addr);



static u32 fdb_salt __read_mostly;



void __init br_fdb_init(void)

{

	br_fdb_cache = kmem_cache_create("bridge_fdb_cache",

					 sizeof(struct net_bridge_fdb_entry),

					 0,

					 SLAB_HWCACHE_ALIGN, NULL, NULL);

	get_random_bytes(&fdb_salt, sizeof(fdb_salt));

}



void __exit br_fdb_fini(void)
@@ -44,24 +49,26 @@ void __exit br_fdb_fini(void) 
/* if topology_changing then use forward_delay (default 15 sec)

 * otherwise keep longer (default 5 minutes)

 */

static __inline__ unsigned long hold_time(const struct net_bridge *br)

static inline unsigned long hold_time(const struct net_bridge *br)

{

	return br->topology_change ? br->forward_delay : br->ageing_time;

}



static __inline__ int has_expired(const struct net_bridge *br,

static inline int has_expired(const struct net_bridge *br,

				  const struct net_bridge_fdb_entry *fdb)

{

	return !fdb->is_static

		&& time_before_eq(fdb->ageing_timer + hold_time(br), jiffies);

}



static __inline__ int br_mac_hash(const unsigned char *mac)

static inline int br_mac_hash(const unsigned char *mac)

{

	return jhash(mac, ETH_ALEN, 0) & (BR_HASH_SIZE - 1);

	/* use 1 byte of OUI cnd 3 bytes of NIC */

	u32 key = get_unaligned((u32 *)(mac + 2));

	return jhash_1word(key, fdb_salt) & (BR_HASH_SIZE - 1);

}



static __inline__ void fdb_delete(struct net_bridge_fdb_entry *f)

static inline void fdb_delete(struct net_bridge_fdb_entry *f)

{

	hlist_del_rcu(&f->hlist);

	br_fdb_put(f);