net: small bug on rxhash calculation

In the current rxhash calculation function, while the
sorting of the ports/addrs is coherent (you get the
same rxhash for packets sharing the same 4-tuple, in
both directions), ports and addrs are sorted
independently. This implies packets from a connection
between the same addresses but crossed ports hash to
the same rxhash.

For example, traffic between A=S:l and B=L:s is hashed
(in both directions) from {L, S, {s, l}}. The same
rxhash is obtained for packets between C=S:s and D=L:l.

This patch ensures that you either swap both addrs and ports,
or you swap none. Traffic between A and B, and traffic
between C and D, get their rxhash from different sources
({L, S, {l, s}} for A<->B, and {L, S, {s, l}} for C<->D)

The patch is co-written with Eric Dumazet <edumazet@google.com>

Signed-off-by: Chema Gonzalez <chema@google.com>
Signed-off-by: Eric Dumazet <edumazet@google.com>
Signed-off-by: David S. Miller <davem@davemloft.net>

diff --git a/net/core/dev.c b/net/core/dev.c
index 83988362805ef1453efb37bfcb3692f59f4edd21..d7fe32c946c1a472b46f086929badaea6900d432 100644 (file)
--- a/net/core/dev.c
+++ b/net/core/dev.c
@@ -2647,15 +2647,16 @@ void __skb_get_rxhash(struct sk_buff *skb)
        if (!skb_flow_dissect(skb, &keys))
                return;
 
-       if (keys.ports) {
-               if ((__force u16)keys.port16[1] < (__force u16)keys.port16[0])
-                       swap(keys.port16[0], keys.port16[1]);
+       if (keys.ports)
                skb->l4_rxhash = 1;
-       }
 
        /* get a consistent hash (same value on both flow directions) */
-       if ((__force u32)keys.dst < (__force u32)keys.src)
+       if (((__force u32)keys.dst < (__force u32)keys.src) ||
+           (((__force u32)keys.dst == (__force u32)keys.src) &&
+            ((__force u16)keys.port16[1] < (__force u16)keys.port16[0]))) {
                swap(keys.dst, keys.src);
+               swap(keys.port16[0], keys.port16[1]);
+       }
 
        hash = jhash_3words((__force u32)keys.dst,
                            (__force u32)keys.src,