[ 31/84] net: small bug on rxhash calculation

Greg Kroah-Hartman
2012-10-11T02:26:20Z

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
@@ -2559,16 +2559,17 @@ __u32 __skb_get_rxhash(struct sk_buff *s
poff = proto_ports_offset(ip_proto);
if (poff >= 0) {
nhoff += ihl * 4 + poff;
- if (pskb_may_pull(skb, nhoff + 4)) {
+ if (pskb_may_pull(skb, nhoff + 4))
ports.v32 = * (__force u32 *) (skb->data + nhoff);
- if (ports.v16[1] < ports.v16[0])
- swap(ports.v16[0], ports.v16[1]);
- }
}

/* get a consistent hash (same value on both flow directions) */
- if (addr2 < addr1)
+ if (addr2 < addr1 ||
+ (addr2 == addr1 &&
+ ports.v16[1] < ports.v16[0])) {
swap(addr1, addr2);
+ swap(ports.v16[0], ports.v16[1]);
+ }

hash = jhash_3words(addr1, addr2, ports.v32, hashrnd);
if (!hash)