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>

1 files changed, 21 insertions, 13 deletions

diff --git a/net/core/dev.c b/net/core/dev.c
index 2eed17bcb2dd..7e2d5274333f 100644
--- 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,