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Commit b6b2fed1 authored by David S. Miller's avatar David S. Miller
Browse files

net: Improve simple_tx_hash(). 



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: default avatarDavid S. Miller <davem@davemloft.net>
parent c3ee8416

net/core/dev.c

+21 −13
Original line number Diff line number Diff line
@@ -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 @@ int dev_hard_start_xmit(struct sk_buff *skb, struct net_device *dev, 
 *          --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,