ipv6: use a stronger hash for tcp

It looks like its possible to open thousands of TCP IPv6
sessions on a server, all landing in a single slot of TCP hash
table. Incoming packets have to lookup sockets in a very
long list.

We should hash all bits from foreign IPv6 addresses, using
a salt and hash mix, not a simple XOR.

inet6_ehashfn() can also separately use the ports, instead
of xoring them.

Reported-by: Neal Cardwell <ncardwell@google.com>
Signed-off-by: Eric Dumazet <edumazet@google.com>
Cc: Yuchung Cheng <ycheng@google.com>
Signed-off-by: David S. Miller <davem@davemloft.net>

1 files changed, 4 insertions, 4 deletions

diff --git a/include/net/inet6_hashtables.h b/include/net/inet6_hashtables.h
index 7ca75cbbf75e..fd4ee016ba5c 100644
--- a/include/net/inet6_hashtables.h
+++ b/include/net/inet6_hashtables.h
@@ -28,16 +28,16 @@
 
 struct inet_hashinfo;
 
-/* I have no idea if this is a good hash for v6 or not. -DaveM */
 static inline unsigned int inet6_ehashfn(struct net *net,
                                 const struct in6_addr *laddr, const u16 lport,
                                 const struct in6_addr *faddr, const __be16 fport)
 {
-        u32 ports = (lport ^ (__force u16)fport);
+        u32 ports = (((u32)lport) << 16) | (__force u32)fport;
 
         return jhash_3words((__force u32)laddr->s6_addr32[3],
-                            (__force u32)faddr->s6_addr32[3],
-                            ports, inet_ehash_secret + net_hash_mix(net));
+                            ipv6_addr_jhash(faddr),
+                            ports,
+                            inet_ehash_secret + net_hash_mix(net));
 }
 
 static inline int inet6_sk_ehashfn(const struct sock *sk)