ipv4: Simplify ARP hash function.
From: David Miller <davem@davemloft.net>
Date: 2011-07-08 17:11:01
Subsystem:
networking [general], networking [ipv4/ipv6], the rest · Maintainers:
"David S. Miller", Eric Dumazet, Jakub Kicinski, Paolo Abeni, David Ahern, Ido Schimmel, Linus Torvalds
Using Jenkins is over the top. If the premise is that the hash_rnd is a random unpredictable key, then: key ^ dev->ifindex ^ hash_rnd results in an unpredictable hash result, even if an attacker controls 'key' and 'dev->ifindex' completely. Therefore, if this hash result is unpredictable, then the final fold phase of: (val >> 8) ^ (val >> 16) ^ (val >> 24) is unpredictable as well. Signed-off-by: David S. Miller <davem@davemloft.net> --- Someone please check my logic :-) This sames ~100 cycles during a neigh_lookup() on my Niagara2 box.
diff --git a/include/net/arp.h b/include/net/arp.h
index 91f0568..d570747 100644
--- a/include/net/arp.h
+++ b/include/net/arp.h@@ -8,6 +8,13 @@ extern struct neigh_table arp_tbl; +static inline u32 arp_hashfn(u32 key, const struct net_device *dev, u32 hash_rnd) +{ + u32 val = key ^ dev->ifindex ^ hash_rnd; + + return (val >> 8) ^ (val >> 16) ^ (val >> 24); +} + extern void arp_init(void); extern int arp_find(unsigned char *haddr, struct sk_buff *skb); extern int arp_ioctl(struct net *net, unsigned int cmd, void __user *arg);
diff --git a/net/ipv4/arp.c b/net/ipv4/arp.c
index 1b74d3b..4412b57 100644
--- a/net/ipv4/arp.c
+++ b/net/ipv4/arp.c@@ -97,7 +97,6 @@ #include <linux/init.h> #include <linux/net.h> #include <linux/rcupdate.h> -#include <linux/jhash.h> #include <linux/slab.h> #ifdef CONFIG_SYSCTL #include <linux/sysctl.h>
@@ -232,7 +231,7 @@ static u32 arp_hash(const void *pkey, const struct net_device *dev, __u32 hash_rnd) { - return jhash_2words(*(u32 *)pkey, dev->ifindex, hash_rnd); + return arp_hashfn(*(u32 *)pkey, dev, hash_rnd); } static int arp_constructor(struct neighbour *neigh)