ipv4: harden fnhe_hashfun()

edumazet · davem330 · commit d546c621542d · 2014-09-05T17:40:33.000-07:00
Lets make this hash function a bit secure, as ICMP attacks are still
in the wild.

Signed-off-by: Eric Dumazet &lt;edumazet@google.com&gt;
Signed-off-by: David S. Miller &lt;davem@davemloft.net&gt;
diff --git a/include/net/ip_fib.h b/include/net/ip_fib.h
@@ -65,7 +65,8 @@ struct fnhe_hash_bucket {
 	struct fib_nh_exception __rcu	*chain;
 };
 
-#define FNHE_HASH_SIZE		2048
+#define FNHE_HASH_SHIFT		11
+#define FNHE_HASH_SIZE		(1 << FNHE_HASH_SHIFT)
 #define FNHE_RECLAIM_DEPTH	5
 
 struct fib_nh {
diff --git a/net/ipv4/route.c b/net/ipv4/route.c
@@ -596,12 +596,12 @@ static struct fib_nh_exception *fnhe_oldest(struct fnhe_hash_bucket *hash)
 
 static inline u32 fnhe_hashfun(__be32 daddr)
 {
+	static u32 fnhe_hashrnd __read_mostly;
 	u32 hval;
 
-	hval = (__force u32) daddr;
-	hval ^= (hval >> 11) ^ (hval >> 22);
-
-	return hval & (FNHE_HASH_SIZE - 1);
+	net_get_random_once(&fnhe_hashrnd, sizeof(fnhe_hashrnd));
+	hval = jhash_1word((__force u32) daddr, fnhe_hashrnd);
+	return hash_32(hval, FNHE_HASH_SHIFT);
 }
 
 static void fill_route_from_fnhe(struct rtable *rt, struct fib_nh_exception *fnhe)

Original file line number	Diff line number	Diff line change
`@@ -596,12 +596,12 @@ static struct fib_nh_exception fnhe_oldest(struct fnhe_hash_bucket hash)`
`596`	`596`
`597`	`597`	`static inline u32 fnhe_hashfun(__be32 daddr)`
`598`	`598`	`{`
	`599`	`+ static u32 fnhe_hashrnd __read_mostly;`
`599`	`600`	`u32 hval;`
`600`	`601`
`601`		`- hval = (__force u32) daddr;`
`602`		`- hval ^= (hval >> 11) ^ (hval >> 22);`
`603`		`-`
`604`		`- return hval & (FNHE_HASH_SIZE - 1);`
	`602`	`+ net_get_random_once(&fnhe_hashrnd, sizeof(fnhe_hashrnd));`
	`603`	`+ hval = jhash_1word((__force u32) daddr, fnhe_hashrnd);`
	`604`	`+ return hash_32(hval, FNHE_HASH_SHIFT);`
`605`	`605`	`}`
`606`	`606`
`607`	`607`	`static void fill_route_from_fnhe(struct rtable rt, struct fib_nh_exception fnhe)`