ipv6: Use universal hash for NDISC.

In order to perform a proper universal hash on a vector of integers,
we have to use different universal hashes on each vector element.

Which means we need 4 different hash randoms for ipv6.

Signed-off-by: David S. Miller <davem@davemloft.net>

include/net/arp.h

@@ -23,7 +23,7 @@ static inline struct neighbour *__ipv4_neigh_lookup(struct neigh_table *tbl, str
 
 	rcu_read_lock_bh();
 	nht = rcu_dereference_bh(tbl->nht);
-	hash_val = arp_hashfn(key, dev, nht->hash_rnd) >> (32 - nht->hash_shift);
+	hash_val = arp_hashfn(key, dev, nht->hash_rnd[0]) >> (32 - nht->hash_shift);
 	for (n = rcu_dereference_bh(nht->hash_buckets[hash_val]);
 	     n != NULL;
 	     n = rcu_dereference_bh(n->next)) {

include/net/ndisc.h

@@ -79,6 +79,15 @@ struct nd_opt_hdr {
 	__u8		nd_opt_len;
 } __packed;
 
+static inline u32 ndisc_hashfn(const void *pkey, const struct net_device *dev, __u32 *hash_rnd)
+{
+	const u32 *p32 = pkey;
+
+	return (((p32[0] ^ dev->ifindex) * hash_rnd[0]) +
+		(p32[1] * hash_rnd[1]) +
+		(p32[2] * hash_rnd[2]) +
+		(p32[3] * hash_rnd[3]));
+}
 
 extern int			ndisc_init(void);
 

include/net/neighbour.h

@@ -139,10 +139,12 @@ struct pneigh_entry {
  *	neighbour table manipulation
  */
 
+#define NEIGH_NUM_HASH_RND	4
+
 struct neigh_hash_table {
 	struct neighbour __rcu	**hash_buckets;
 	unsigned int		hash_shift;
-	__u32			hash_rnd;
+	__u32			hash_rnd[NEIGH_NUM_HASH_RND];
 	struct rcu_head		rcu;
 };
 
@@ -154,7 +156,7 @@ struct neigh_table {
 	int			key_len;
 	__u32			(*hash)(const void *pkey,
 					const struct net_device *dev,
-					__u32 hash_rnd);
+					__u32 *hash_rnd);
 	int			(*constructor)(struct neighbour *);
 	int			(*pconstructor)(struct pneigh_entry *);
 	void			(*pdestructor)(struct pneigh_entry *);

net/core/neighbour.c

@@ -322,11 +322,18 @@ out_entries:
 	goto out;
 }
 
+static void neigh_get_hash_rnd(u32 *x)
+{
+	get_random_bytes(x, sizeof(*x));
+	*x |= 1;
+}
+
 static struct neigh_hash_table *neigh_hash_alloc(unsigned int shift)
 {
 	size_t size = (1 << shift) * sizeof(struct neighbour *);
 	struct neigh_hash_table *ret;
 	struct neighbour __rcu **buckets;
+	int i;
 
 	ret = kmalloc(sizeof(*ret), GFP_ATOMIC);
 	if (!ret)
@@ -343,8 +350,8 @@ static struct neigh_hash_table *neigh_hash_alloc(unsigned int shift)
 	}
 	ret->hash_buckets = buckets;
 	ret->hash_shift = shift;
-	get_random_bytes(&ret->hash_rnd, sizeof(ret->hash_rnd));
-	ret->hash_rnd |= 1;
+	for (i = 0; i < NEIGH_NUM_HASH_RND; i++)
+		neigh_get_hash_rnd(&ret->hash_rnd[i]);
 	return ret;
 }
 
@@ -1828,7 +1835,7 @@ static int neightbl_fill_info(struct sk_buff *skb, struct neigh_table *tbl,
 
 		rcu_read_lock_bh();
 		nht = rcu_dereference_bh(tbl->nht);
-		ndc.ndtc_hash_rnd = nht->hash_rnd;
+		ndc.ndtc_hash_rnd = nht->hash_rnd[0];
 		ndc.ndtc_hash_mask = ((1 << nht->hash_shift) - 1);
 		rcu_read_unlock_bh();
 

net/decnet/dn_neigh.c

@@ -88,9 +88,9 @@ static const struct neigh_ops dn_phase3_ops = {
 
 static u32 dn_neigh_hash(const void *pkey,
 			 const struct net_device *dev,
-			 __u32 hash_rnd)
+			 __u32 *hash_rnd)
 {
-	return jhash_2words(*(__u16 *)pkey, 0, hash_rnd);
+	return jhash_2words(*(__u16 *)pkey, 0, hash_rnd[0]);
 }
 
 struct neigh_table dn_neigh_table = {

net/ipv4/arp.c

@@ -121,7 +121,7 @@
 /*
  *	Interface to generic neighbour cache.
  */
-static u32 arp_hash(const void *pkey, const struct net_device *dev, __u32 rnd);
+static u32 arp_hash(const void *pkey, const struct net_device *dev, __u32 *hash_rnd);
 static int arp_constructor(struct neighbour *neigh);
 static void arp_solicit(struct neighbour *neigh, struct sk_buff *skb);
 static void arp_error_report(struct neighbour *neigh, struct sk_buff *skb);
@@ -215,9 +215,9 @@ int arp_mc_map(__be32 addr, u8 *haddr, struct net_device *dev, int dir)
 
 static u32 arp_hash(const void *pkey,
 		    const struct net_device *dev,
-		    __u32 hash_rnd)
+		    __u32 *hash_rnd)
 {
-	return arp_hashfn(*(u32 *)pkey, dev, hash_rnd);
+	return arp_hashfn(*(u32 *)pkey, dev, *hash_rnd);
 }
 
 static int arp_constructor(struct neighbour *neigh)

net/ipv6/ndisc.c

@@ -93,7 +93,7 @@
 
 static u32 ndisc_hash(const void *pkey,
 		      const struct net_device *dev,
-		      __u32 rnd);
+		      __u32 *hash_rnd);
 static int ndisc_constructor(struct neighbour *neigh);
 static void ndisc_solicit(struct neighbour *neigh, struct sk_buff *skb);
 static void ndisc_error_report(struct neighbour *neigh, struct sk_buff *skb);
@@ -349,16 +349,9 @@ EXPORT_SYMBOL(ndisc_mc_map);
 
 static u32 ndisc_hash(const void *pkey,
 		      const struct net_device *dev,
-		      __u32 hash_rnd)
+		      __u32 *hash_rnd)
 {
-	const u32 *p32 = pkey;
-	u32 addr_hash, i;
-
-	addr_hash = 0;
-	for (i = 0; i < (sizeof(struct in6_addr) / sizeof(u32)); i++)
-		addr_hash ^= *p32++;
-
-	return jhash_2words(addr_hash, dev->ifindex, hash_rnd);
+	return ndisc_hashfn(pkey, dev, hash_rnd);
 }
 
 static int ndisc_constructor(struct neighbour *neigh)