packet: Use symmetric hash for PACKET_FANOUT_HASH.
authorDavid S. Miller <davem@davemloft.net>
Fri, 1 Jul 2016 20:07:50 +0000 (16:07 -0400)
committerDavid S. Miller <davem@davemloft.net>
Fri, 1 Jul 2016 20:07:50 +0000 (16:07 -0400)
commiteb70db8756717b90c01ccc765fdefc4dd969fc74
tree80c89c33271947ab3785bcaeb66bd21a8b416c7d
parent08df7bc5001e7fc8bdb0a74e04ad2db5f797ed3d
packet: Use symmetric hash for PACKET_FANOUT_HASH.

People who use PACKET_FANOUT_HASH want a symmetric hash, meaning that
they want packets going in both directions on a flow to hash to the
same bucket.

The core kernel SKB hash became non-symmetric when the ipv6 flow label
and other entities were incorporated into the standard flow hash order
to increase entropy.

But there are no users of PACKET_FANOUT_HASH who want an assymetric
hash, they all want a symmetric one.

Therefore, use the flow dissector to compute a flat symmetric hash
over only the protocol, addresses and ports.  This hash does not get
installed into and override the normal skb hash, so this change has
no effect whatsoever on the rest of the stack.

Reported-by: Eric Leblond <eric@regit.org>
Tested-by: Eric Leblond <eric@regit.org>
Signed-off-by: David S. Miller <davem@davemloft.net>
include/linux/skbuff.h
net/core/flow_dissector.c
net/packet/af_packet.c