bgpd: fix issue in capability negotiation (BZ#700)

Address problem where bgpd would reject a session if a peer sent some
capabilities in its Open message, but did not include a Multiprotocol
extensions capability. Note that the session would come up if there
were no capabilities at all in the Open message.

  * Add the 'mp_capability' out parameter to
    bgp_capability_parse(). Set it to '1' if a Multiprotocol
    extensions capability is encountered.

  * Switch on 'mp_capability' instead of 'capability' in the calling
    functions to determine if the peer indicated the set of AFI/SAFIs
    it supports.

    The net result is that when a peer does not send an MP capability,
    it is assumed to support the AFI/SAFIs configured for it locally.

1 files changed, 10 insertions, 5 deletions

diff --git a/bgpd/bgp_packet.c b/bgpd/bgp_packet.c
index 5d8087a8..390b5563 100644
--- a/bgpd/bgp_packet.c
+++ b/bgpd/bgp_packet.c
@@ -1152,7 +1152,7 @@ bgp_open_receive (struct peer *peer, bgp_size_t size)
   as_t as4 = 0;
   struct peer *realpeer;
   struct in_addr remote_id;
-  int capability;
+  int mp_capability;
   u_int8_t notify_data_remote_as[2];
   u_int8_t notify_data_remote_id[4];
 
@@ -1174,7 +1174,7 @@ bgp_open_receive (struct peer *peer, bgp_size_t size)
 	        inet_ntoa (remote_id));
   
   /* BEGIN to read the capability here, but dont do it yet */
-  capability = 0;
+  mp_capability = 0;
   optlen = stream_getc (peer->ibuf);
   
   if (optlen != 0)
@@ -1459,7 +1459,7 @@ bgp_open_receive (struct peer *peer, bgp_size_t size)
   /* Open option part parse. */
   if (optlen != 0) 
     {
-      if ((ret = bgp_open_option_parse (peer, optlen, &capability)) < 0)
+      if ((ret = bgp_open_option_parse (peer, optlen, &mp_capability)) < 0)
         {
           bgp_notify_send (peer,
                  BGP_NOTIFY_OPEN_ERR,
@@ -1474,8 +1474,13 @@ bgp_open_receive (struct peer *peer, bgp_size_t size)
 		   peer->host);
     }
 
-  /* Override capability. */
-  if (! capability || CHECK_FLAG (peer->flags, PEER_FLAG_OVERRIDE_CAPABILITY))
+  /* 
+   * Assume that the peer supports the locally configured set of
+   * AFI/SAFIs if the peer did not send us any Mulitiprotocol
+   * capabilities, or if 'override-capability' is configured.
+   */
+  if (! mp_capability ||
+      CHECK_FLAG (peer->flags, PEER_FLAG_OVERRIDE_CAPABILITY))
     {
       peer->afc_nego[AFI_IP][SAFI_UNICAST] = peer->afc[AFI_IP][SAFI_UNICAST];
       peer->afc_nego[AFI_IP][SAFI_MULTICAST] = peer->afc[AFI_IP][SAFI_MULTICAST];