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: David S. Miller <davem@davemloft.net>

diff --git a/net/core/dev.c b/net/core/dev.c
index 2eed17b..7e2d527 100644 (file)
--- a/net/core/dev.c
+++ b/net/core/dev.c
@@ -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,