releases/4.6.5/packet-use-symmetric-hash-for-packet_fanout_hash.patch

   1 From foo@baz Thu Jul 14 07:36:41 JST 2016
   2 From: "David S. Miller" <davem@davemloft.net>
   3 Date: Fri, 1 Jul 2016 16:07:50 -0400
   4 Subject: packet: Use symmetric hash for PACKET_FANOUT_HASH.
   5
   6 From: "David S. Miller" <davem@davemloft.net>
   7
   8 [ Upstream commit eb70db8756717b90c01ccc765fdefc4dd969fc74 ]
   9
  10 People who use PACKET_FANOUT_HASH want a symmetric hash, meaning that
  11 they want packets going in both directions on a flow to hash to the
  12 same bucket.
  13
  14 The core kernel SKB hash became non-symmetric when the ipv6 flow label
  15 and other entities were incorporated into the standard flow hash order
  16 to increase entropy.
  17
  18 But there are no users of PACKET_FANOUT_HASH who want an assymetric
  19 hash, they all want a symmetric one.
  20
  21 Therefore, use the flow dissector to compute a flat symmetric hash
  22 over only the protocol, addresses and ports.  This hash does not get
  23 installed into and override the normal skb hash, so this change has
  24 no effect whatsoever on the rest of the stack.
  25
  26 Reported-by: Eric Leblond <eric@regit.org>
  27 Tested-by: Eric Leblond <eric@regit.org>
  28 Signed-off-by: David S. Miller <davem@davemloft.net>
  29 Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>
  30 ---
  31  include/linux/skbuff.h    |    1 +
  32  net/core/flow_dissector.c |   43 +++++++++++++++++++++++++++++++++++++++++++
  33  net/packet/af_packet.c    |    2 +-
  34  3 files changed, 45 insertions(+), 1 deletion(-)
  35
  36 --- a/include/linux/skbuff.h
  37 +++ b/include/linux/skbuff.h
  38 @@ -1062,6 +1062,7 @@ __skb_set_sw_hash(struct sk_buff *skb, _
  39  }
  40
  41  void __skb_get_hash(struct sk_buff *skb);
  42 +u32 __skb_get_hash_symmetric(struct sk_buff *skb);
  43  u32 skb_get_poff(const struct sk_buff *skb);
  44  u32 __skb_get_poff(const struct sk_buff *skb, void *data,
  45                    const struct flow_keys *keys, int hlen);
  46 --- a/net/core/flow_dissector.c
  47 +++ b/net/core/flow_dissector.c
  48 @@ -651,6 +651,23 @@ void make_flow_keys_digest(struct flow_k
  49  }
  50  EXPORT_SYMBOL(make_flow_keys_digest);
  51
  52 +static struct flow_dissector flow_keys_dissector_symmetric __read_mostly;
  53 +
  54 +u32 __skb_get_hash_symmetric(struct sk_buff *skb)
  55 +{
  56 +       struct flow_keys keys;
  57 +
  58 +       __flow_hash_secret_init();
  59 +
  60 +       memset(&keys, 0, sizeof(keys));
  61 +       __skb_flow_dissect(skb, &flow_keys_dissector_symmetric, &keys,
  62 +                          NULL, 0, 0, 0,
  63 +                          FLOW_DISSECTOR_F_STOP_AT_FLOW_LABEL);
  64 +
  65 +       return __flow_hash_from_keys(&keys, hashrnd);
  66 +}
  67 +EXPORT_SYMBOL_GPL(__skb_get_hash_symmetric);
  68 +
  69  /**
  70   * __skb_get_hash: calculate a flow hash
  71   * @skb: sk_buff to calculate flow hash from
  72 @@ -868,6 +885,29 @@ static const struct flow_dissector_key f
  73         },
  74  };
  75
  76 +static const struct flow_dissector_key flow_keys_dissector_symmetric_keys[] = {
  77 +       {
  78 +               .key_id = FLOW_DISSECTOR_KEY_CONTROL,
  79 +               .offset = offsetof(struct flow_keys, control),
  80 +       },
  81 +       {
  82 +               .key_id = FLOW_DISSECTOR_KEY_BASIC,
  83 +               .offset = offsetof(struct flow_keys, basic),
  84 +       },
  85 +       {
  86 +               .key_id = FLOW_DISSECTOR_KEY_IPV4_ADDRS,
  87 +               .offset = offsetof(struct flow_keys, addrs.v4addrs),
  88 +       },
  89 +       {
  90 +               .key_id = FLOW_DISSECTOR_KEY_IPV6_ADDRS,
  91 +               .offset = offsetof(struct flow_keys, addrs.v6addrs),
  92 +       },
  93 +       {
  94 +               .key_id = FLOW_DISSECTOR_KEY_PORTS,
  95 +               .offset = offsetof(struct flow_keys, ports),
  96 +       },
  97 +};
  98 +
  99  static const struct flow_dissector_key flow_keys_buf_dissector_keys[] = {
 100         {
 101                 .key_id = FLOW_DISSECTOR_KEY_CONTROL,
 102 @@ -889,6 +929,9 @@ static int __init init_default_flow_diss
 103         skb_flow_dissector_init(&flow_keys_dissector,
 104                                 flow_keys_dissector_keys,
 105                                 ARRAY_SIZE(flow_keys_dissector_keys));
 106 +       skb_flow_dissector_init(&flow_keys_dissector_symmetric,
 107 +                               flow_keys_dissector_symmetric_keys,
 108 +                               ARRAY_SIZE(flow_keys_dissector_symmetric_keys));
 109         skb_flow_dissector_init(&flow_keys_buf_dissector,
 110                                 flow_keys_buf_dissector_keys,
 111                                 ARRAY_SIZE(flow_keys_buf_dissector_keys));
 112 --- a/net/packet/af_packet.c
 113 +++ b/net/packet/af_packet.c
 114 @@ -1340,7 +1340,7 @@ static unsigned int fanout_demux_hash(st
 115                                       struct sk_buff *skb,
 116                                       unsigned int num)
 117  {
 118 -       return reciprocal_scale(skb_get_hash(skb), num);
 119 +       return reciprocal_scale(__skb_get_hash_symmetric(skb), num);
 120  }
 121
 122  static unsigned int fanout_demux_lb(struct packet_fanout *f,