batman-adv/patches/0036-batman-adv-fix-packet-loss-for-broadcasted-DHCP-pack.patch

   1 From: Linus Lüssing <linus.luessing@c0d3.blue>
   2 Date: Thu, 22 Mar 2018 00:21:32 +0100
   3 Subject: [PATCH] batman-adv: fix packet loss for broadcasted DHCP packets to a server
   4
   5 DHCP connectivity issues can currently occur if the following conditions
   6 are met:
   7
   8 1) A DHCP packet from a client to a server
   9 2) This packet has a multicast destination
  10 3) This destination has a matching entry in the translation table
  11    (FF:FF:FF:FF:FF:FF for IPv4, 33:33:00:01:00:02/33:33:00:01:00:03
  12     for IPv6)
  13 4) The orig-node determined by TT for the multicast destination
  14    does not match the orig-node determined by best-gateway-selection
  15
  16 In this case the DHCP packet will be dropped.
  17
  18 The "gateway-out-of-range" check is supposed to only be applied to
  19 unicasted DHCP packets to a specific DHCP server.
  20
  21 In that case dropping the the unicasted frame forces the client to
  22 retry via a broadcasted one, but now directed to the new best
  23 gateway.
  24
  25 A DHCP packet with broadcast/multicast destination is already ensured to
  26 always be delivered to the best gateway. Dropping a multicasted
  27 DHCP packet here will only prevent completing DHCP as there is no
  28 other fallback.
  29
  30 So far, it seems the unicast check was implicitly performed by
  31 expecting the batadv_transtable_search() to return NULL for multicast
  32 destinations. However, a multicast address could have always ended up in
  33 the translation table and in fact is now common.
  34
  35 To fix this potential loss of a DHCP client-to-server packet to a
  36 multicast address this patch adds an explicit multicast destination
  37 check to reliably bail out of the gateway-out-of-range check for such
  38 destinations.
  39
  40 The issue and fix were tested in the following three node setup:
  41
  42 - Line topology, A-B-C
  43 - A: gateway client, DHCP client
  44 - B: gateway server, hop-penalty increased: 30->60, DHCP server
  45 - C: gateway server, code modifications to announce FF:FF:FF:FF:FF:FF
  46
  47 Without this patch, A would never transmit its DHCP Discover packet
  48 due to an always "out-of-range" condition. With this patch,
  49 a full DHCP handshake between A and B was possible again.
  50
  51 Fixes: afae4e42aae6 ("batman-adv: refactoring gateway handling code")
  52 Signed-off-by: Linus Lüssing <linus.luessing@c0d3.blue>
  53 Signed-off-by: Sven Eckelmann <sven@narfation.org>
  54
  55 Origin: upstream, https://git.open-mesh.org/batman-adv.git/commit/49b2132f0fe2753a3b46103db9719898c5cd44aa
  56 ---
  57  net/batman-adv/gateway_client.c | 5 ++++-
  58  1 file changed, 4 insertions(+), 1 deletion(-)
  59
  60 diff --git a/net/batman-adv/gateway_client.c b/net/batman-adv/gateway_client.c
  61 index 52b8bd6ec43183519a63483950c2e886e47a6f9e..f1fdf4e7f5c3ce7f20339dcee3b6e43290ea3b4e 100644
  62 --- a/net/batman-adv/gateway_client.c
  63 +++ b/net/batman-adv/gateway_client.c
  64 @@ -705,7 +705,7 @@ bool batadv_gw_out_of_range(struct batadv_priv *bat_priv,
  65  {
  66         struct batadv_neigh_node *neigh_curr = NULL;
  67         struct batadv_neigh_node *neigh_old = NULL;
  68 -       struct batadv_orig_node *orig_dst_node;
  69 +       struct batadv_orig_node *orig_dst_node = NULL;
  70         struct batadv_gw_node *gw_node = NULL;
  71         struct batadv_gw_node *curr_gw = NULL;
  72         struct batadv_neigh_ifinfo *curr_ifinfo, *old_ifinfo;
  73 @@ -716,6 +716,9 @@ bool batadv_gw_out_of_range(struct batadv_priv *bat_priv,
  74
  75         vid = batadv_get_vid(skb, 0);
  76
  77 +       if (is_multicast_ether_addr(ethhdr->h_dest))
  78 +               goto out;
  79 +
  80         orig_dst_node = batadv_transtable_search(bat_priv, ethhdr->h_source,
  81                                                  ethhdr->h_dest, vid);
  82         if (!orig_dst_node)