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net: Improve simple_tx_hash().

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Based upon feedback from Eric Dumazet and Andi Kleen.

Cure several deficiencies in simple_tx_hash() by using
jhash + reciprocol multiply.

1) Eliminates expensive modulus operation.

2) Makes hash less attackable by using random seed.

3) Eliminates endianness hash distribution issues.

Signed-off-by: David S. Miller <davem@davemloft.net>
This commit is contained in:
David S. Miller 2008-07-21 09:48:06 -07:00
parent c3ee84163e
commit b6b2fed1f4
1 changed files with 21 additions and 13 deletions
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34
net/core/dev.c
View File

@ -124,6 +124,8 @@
#include <linux/ip.h>
#include <linux/ipv6.h>
#include <linux/in.h>
#include <linux/jhash.h>
#include <linux/random.h>
#include "net-sysfs.h"
@ -1668,34 +1670,37 @@ out_kfree_skb:
* --BLG
*/
static u32 simple_tx_hashrnd;
static int simple_tx_hashrnd_initialized = 0;
static u16 simple_tx_hash(struct net_device *dev, struct sk_buff *skb)
{
u32 *addr, *ports, hash, ihl;
u32 addr1, addr2, ports;
u32 hash, ihl;
u8 ip_proto;
int alen;
if (unlikely(!simple_tx_hashrnd_initialized)) {
get_random_bytes(&simple_tx_hashrnd, 4);
simple_tx_hashrnd_initialized = 1;
}
switch (skb->protocol) {
case __constant_htons(ETH_P_IP):
ip_proto = ip_hdr(skb)->protocol;
addr = &ip_hdr(skb)->saddr;
addr1 = ip_hdr(skb)->saddr;
addr2 = ip_hdr(skb)->daddr;
ihl = ip_hdr(skb)->ihl;
alen = 2;
break;
case __constant_htons(ETH_P_IPV6):
ip_proto = ipv6_hdr(skb)->nexthdr;
addr = &ipv6_hdr(skb)->saddr.s6_addr32[0];
addr1 = ipv6_hdr(skb)->saddr.s6_addr32[3];
addr2 = ipv6_hdr(skb)->daddr.s6_addr32[3];
ihl = (40 >> 2);
alen = 8;
break;
default:
return 0;
}
ports = (u32 *) (skb_network_header(skb) + (ihl * 4));
hash = 0;
while (alen--)
hash ^= *addr++;
switch (ip_proto) {
case IPPROTO_TCP:
@ -1705,14 +1710,17 @@ static u16 simple_tx_hash(struct net_device *dev, struct sk_buff *skb)
case IPPROTO_AH:
case IPPROTO_SCTP:
case IPPROTO_UDPLITE:
hash ^= *ports;
ports = *((u32 *) (skb_network_header(skb) + (ihl * 4)));
break;
default:
ports = 0;
break;
}
return hash % dev->real_num_tx_queues;
hash = jhash_3words(addr1, addr2, ports, simple_tx_hashrnd);
return (u16) (((u64) hash * dev->real_num_tx_queues) >> 32);
}
static struct netdev_queue *dev_pick_tx(struct net_device *dev,