netdev - [PATCH net-next] ipv4: harden fnhe

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Date:	Thu, 04 Sep 2014 08:21:31 -0700
From:	Eric Dumazet <eric.dumazet@...il.com>
To:	David Miller <davem@...emloft.net>
Cc:	netdev <netdev@...r.kernel.org>,
	Neal Cardwell <ncardwell@...gle.com>
Subject: [PATCH net-next] ipv4: harden fnhe_hashfun()

From: Eric Dumazet <edumazet@...gle.com>

Lets make this hash function a bit secure, as ICMP attacks are still
in the wild.

Signed-off-by: Eric Dumazet <edumazet@...gle.com>
---
 include/net/ip_fib.h |    3 ++-
 net/ipv4/route.c     |    8 ++++----
 2 files changed, 6 insertions(+), 5 deletions(-)

diff --git a/include/net/ip_fib.h b/include/net/ip_fib.h
index 9922093f575e..6c8f00236a47 100644
--- 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
index eaa4b000c7b4..deb7a2ec3669 100644
--- 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)


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