bgpd: Add peers back to peer hash when peer_xfer_conn fails

It was noticed that occassionally peering failed in a testbed
upon investigation it was found that the peer was not in the
peer hash and we saw these failure messages:

Aug 25 21:31:15 doca-hbn-service-bf3-s06-1-ipmi bgpd[3048]: %NOTIFICATION: sent to neighbor 2001:cafe:1ead:4::4 4/0 (Hold Timer Expired) 0 bytes
Aug 25 21:31:22 doca-hbn-service-bf3-s06-1-ipmi bgpd[3048]: [EC 100663299] Can't get remote address and port: Transport endpoint is not connected
Aug 25 21:31:22 doca-hbn-service-bf3-s06-1-ipmi bgpd[3048]: [EC 100663299] %bgp_getsockname() failed for  peer 2001:cafe:1ead:4::4 fd 27 (from_peer fd -1)
Aug 25 21:31:22 doca-hbn-service-bf3-s06-1-ipmi bgpd[3048]: [EC 33554464] %Neighbor failed in xfer_conn

root@doca-hbn-service-bf3-s06-1-ipmi:/var/log/hbn/frr# vtysh -c 'show bgp peerhash' | grep 2001:cafe:1ead:4::4
root@doca-hbn-service-bf3-s06-1-ipmi:/var/log/hbn/frr#

Upon looking at the code the peer_xfer_conn function can fail
and the bgp_establish code will then return before adding the
peer back to the peerhash.

This is only part of the failure.  The peer also appears to
be in a state where it is no longer initiating connection attempts
but that will be another commited fix when we figure that one out.

Signed-off-by: Donald Sharp <[email protected]>

bgpd/bgp_fsm.c

@@ -2137,6 +2137,7 @@ bgp_establish(struct peer_connection *connection)
 	struct peer *other;
 	int status;
 	struct peer *peer = connection->peer;
+	struct peer *orig = peer;
 
 	other = peer->doppelganger;
 	hash_release(peer->bgp->peerhash, peer);
@@ -2146,6 +2147,17 @@ bgp_establish(struct peer_connection *connection)
 	peer = peer_xfer_conn(peer);
 	if (!peer) {
 		flog_err(EC_BGP_CONNECT, "%%Neighbor failed in xfer_conn");
+
+		/*
+		 * A failure of peer_xfer_conn but not putting the peers
+		 * back in the hash ends up with a situation where incoming
+		 * connections are rejected, as that the peer is not found
+		 * when a lookup is done
+		 */
+		(void)hash_get(orig->bgp->peerhash, orig, hash_alloc_intern);
+		if (other)
+			(void)hash_get(other->bgp->peerhash, other,
+				       hash_alloc_intern);
 		return BGP_FSM_FAILURE;
 	}