Patch "packet: Use symmetric hash for PACKET_FANOUT_HASH." has been added to the 4.4-stable tree

[<gregkh@linuxfoundation.org>]

This is a note to let you know that I've just added the patch titled

    packet: Use symmetric hash for PACKET_FANOUT_HASH.

to the 4.4-stable tree which can be found at:
    http://www.kernel.org/git/?p=linux/kernel/git/stable/stable-queue.git;a=summary

The filename of the patch is:
     packet-use-symmetric-hash-for-packet_fanout_hash.patch
and it can be found in the queue-4.4 subdirectory.

If you, or anyone else, feels it should not be added to the stable tree,
please let <stable@vger.kernel.org> know about it.


>From foo@baz Thu Jul 14 07:36:31 JST 2016
From: "David S. Miller" <davem@davemloft.net>
Date: Fri, 1 Jul 2016 16:07:50 -0400
Subject: packet: Use symmetric hash for PACKET_FANOUT_HASH.

From: "David S. Miller" <davem@davemloft.net>

[ Upstream commit eb70db8756717b90c01ccc765fdefc4dd969fc74 ]

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>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>
---
 include/linux/skbuff.h    |    1 +
 net/core/flow_dissector.c |   43 +++++++++++++++++++++++++++++++++++++++++++
 net/packet/af_packet.c    |    2 +-
 3 files changed, 45 insertions(+), 1 deletion(-)

--- a/include/linux/skbuff.h
+++ b/include/linux/skbuff.h
@@ -982,6 +982,7 @@ __skb_set_sw_hash(struct sk_buff *skb, _
 }
 
 void __skb_get_hash(struct sk_buff *skb);
+u32 __skb_get_hash_symmetric(struct sk_buff *skb);
 u32 skb_get_poff(const struct sk_buff *skb);
 u32 __skb_get_poff(const struct sk_buff *skb, void *data,
 		   const struct flow_keys *keys, int hlen);
--- a/net/core/flow_dissector.c
+++ b/net/core/flow_dissector.c
@@ -662,6 +662,23 @@ void make_flow_keys_digest(struct flow_k
 }
 EXPORT_SYMBOL(make_flow_keys_digest);
 
+static struct flow_dissector flow_keys_dissector_symmetric __read_mostly;
+
+u32 __skb_get_hash_symmetric(struct sk_buff *skb)
+{
+	struct flow_keys keys;
+
+	__flow_hash_secret_init();
+
+	memset(&keys, 0, sizeof(keys));
+	__skb_flow_dissect(skb, &flow_keys_dissector_symmetric, &keys,
+			   NULL, 0, 0, 0,
+			   FLOW_DISSECTOR_F_STOP_AT_FLOW_LABEL);
+
+	return __flow_hash_from_keys(&keys, hashrnd);
+}
+EXPORT_SYMBOL_GPL(__skb_get_hash_symmetric);
+
 /**
  * __skb_get_hash: calculate a flow hash
  * @skb: sk_buff to calculate flow hash from
@@ -874,6 +891,29 @@ static const struct flow_dissector_key f
 	},
 };
 
+static const struct flow_dissector_key flow_keys_dissector_symmetric_keys[] = {
+	{
+		.key_id = FLOW_DISSECTOR_KEY_CONTROL,
+		.offset = offsetof(struct flow_keys, control),
+	},
+	{
+		.key_id = FLOW_DISSECTOR_KEY_BASIC,
+		.offset = offsetof(struct flow_keys, basic),
+	},
+	{
+		.key_id = FLOW_DISSECTOR_KEY_IPV4_ADDRS,
+		.offset = offsetof(struct flow_keys, addrs.v4addrs),
+	},
+	{
+		.key_id = FLOW_DISSECTOR_KEY_IPV6_ADDRS,
+		.offset = offsetof(struct flow_keys, addrs.v6addrs),
+	},
+	{
+		.key_id = FLOW_DISSECTOR_KEY_PORTS,
+		.offset = offsetof(struct flow_keys, ports),
+	},
+};
+
 static const struct flow_dissector_key flow_keys_buf_dissector_keys[] = {
 	{
 		.key_id = FLOW_DISSECTOR_KEY_CONTROL,
@@ -895,6 +935,9 @@ static int __init init_default_flow_diss
 	skb_flow_dissector_init(&flow_keys_dissector,
 				flow_keys_dissector_keys,
 				ARRAY_SIZE(flow_keys_dissector_keys));
+	skb_flow_dissector_init(&flow_keys_dissector_symmetric,
+				flow_keys_dissector_symmetric_keys,
+				ARRAY_SIZE(flow_keys_dissector_symmetric_keys));
 	skb_flow_dissector_init(&flow_keys_buf_dissector,
 				flow_keys_buf_dissector_keys,
 				ARRAY_SIZE(flow_keys_buf_dissector_keys));
--- a/net/packet/af_packet.c
+++ b/net/packet/af_packet.c
@@ -1341,7 +1341,7 @@ static unsigned int fanout_demux_hash(st
 				      struct sk_buff *skb,
 				      unsigned int num)
 {
-	return reciprocal_scale(skb_get_hash(skb), num);
+	return reciprocal_scale(__skb_get_hash_symmetric(skb), num);
 }
 
 static unsigned int fanout_demux_lb(struct packet_fanout *f,


Patches currently in stable-queue which might be from davem@davemloft.net are

queue-4.4/cdc_ncm-workaround-for-em7455-silent-data-interface.patch
queue-4.4/ipv6-fix-mem-leak-in-rt6i_pcpu.patch
queue-4.4/net_sched-fix-mirrored-packets-checksum.patch
queue-4.4/packet-use-symmetric-hash-for-packet_fanout_hash.patch