[ 050/133] net: small bug on rxhash calculation

Greg Kroah-Hartman
2012-10-10T23:19:51Z

From: Chema Gonzalez <chema@google.com>

[ Upstream commit 6862234238e84648c305526af2edd98badcad1e0 ]

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>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>
---
net/core/dev.c | 11 ++++++-----
1 file changed, 6 insertions(+), 5 deletions(-)

--- a/net/core/dev.c
+++ b/net/core/dev.c
@@ -2615,15 +2615,16 @@ void __skb_get_rxhash(struct sk_buff *sk
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,