FIB recusrion loop checks traverse midchain adjacencies

if a tunnel's destination address is reachable through the tunnel
(see example config belwo) then search for and detect a recursion
loop and don't stack the adjacency. Otherwise this results in a
nasty surprise.

DBGvpp# loop cre
DBGvpp# set int state loop0 up
DBGvpp# set int ip addr loop0 10.0.0.1/24
DBGvpp# create gre tunnel src 10.0.0.1 dst 1.1.1.1
DBGvpp# set int state gre0 up
DBGvpp# set int unnum gre0 use loop0
DBGvpp# ip route 1.1.1.1/32 via gre0

DBGvpp# sh ip fib 1.1.1.1
ipv4-VRF:0, fib_index:0, flow hash:[src dst sport dport proto ] locks:[src:plugin-hi:2, src:default-route:1, ]
1.1.1.1/32 fib:0 index:11 locks:4   <<< this is entry #11
  src:CLI refs:1 entry-flags:attached, src-flags:added,contributing,active,
    path-list:[14] locks:2 flags:shared,looped, uPRF-list:12 len:1 itfs:[2, ]
      path:[14] pl-index:14 ip4 weight=1 pref=0 attached-nexthop:  oper-flags:recursive-loop,resolved, cfg-flags:attached,
        1.1.1.1 gre0 (p2p)
          [@0]: ipv4 via 0.0.0.0 gre0: mtu:9000 4500000000000000fe2fb0cc0a0000010101010100000800
             stacked-on entry:11:  <<<< and the midchain forwards via entry #11
               [@2]: dpo-drop ip4

  src:recursive-resolution refs:1 src-flags:added, cover:-1

 forwarding:   unicast-ip4-chain
  [@0]: dpo-load-balance: [proto:ip4 index:13 buckets:1 uRPF:12 to:[0:0]]
    [0] [@6]: ipv4 via 0.0.0.0 gre0: mtu:9000 4500000000000000fe2fb0cc0a0000010101010100000800
        stacked-on entry:11:
          [@2]: dpo-drop ip4

DBGvpp# sh adj 1
[@1] ipv4 via 0.0.0.0 gre0: mtu:9000 4500000000000000fe2fb0cc0a0000010101010100000800
  stacked-on entry:11:
    [@2]: dpo-drop ip4
   flags:midchain-ip-stack midchain-looped  <<<<< this is a loop
   counts:[0:0]
   locks:4
 delegates:

 children:
  {path:14}

Change-Id: I39b82bd1ea439be4611c88b130d40289fa0c1b59
Signed-off-by: Neale Ranns <nranns@cisco.com>

1 files changed, 14 insertions, 2 deletions

diff --git a/src/vnet/fib/fib_path.c b/src/vnet/fib/fib_path.c
index baf8275d181..f528c67677f 100644
--- a/src/vnet/fib/fib_path.c
+++ b/src/vnet/fib/fib_path.c
@@ -1802,7 +1802,7 @@ fib_path_recursive_loop_detect (fib_node_index_t path_index,
 	{
 	    /*
 	     * no loop here yet. keep forward walking the graph.
-	     */	    
+	     */
 	    if (fib_entry_recursive_loop_detect(path->fp_via_fib, entry_indicies))
 	    {
 		FIB_PATH_DBG(path, "recursive loop formed");
@@ -1818,6 +1818,18 @@ fib_path_recursive_loop_detect (fib_node_index_t path_index,
     }
     case FIB_PATH_TYPE_ATTACHED_NEXT_HOP:
     case FIB_PATH_TYPE_ATTACHED:
+	if (adj_recursive_loop_detect(path->fp_dpo.dpoi_index,
+                                      entry_indicies))
+	{
+	    FIB_PATH_DBG(path, "recursive loop formed");
+	    path->fp_oper_flags |= FIB_PATH_OPER_FLAG_RECURSIVE_LOOP;
+	}
+        else
+        {
+            FIB_PATH_DBG(path, "recursive loop cleared");
+            path->fp_oper_flags &= ~FIB_PATH_OPER_FLAG_RECURSIVE_LOOP;
+        }
+        break;
     case FIB_PATH_TYPE_SPECIAL:
     case FIB_PATH_TYPE_DEAG:
     case FIB_PATH_TYPE_DVR:
@@ -2690,7 +2702,7 @@ show_fib_path_command (vlib_main_t * vm,
 	    path = fib_path_get(pi);
 	    u8 *s = format(NULL, "%U", format_fib_path, pi, 1,
                            FIB_PATH_FORMAT_FLAGS_NONE);
-	    s = format(s, "children:");
+	    s = format(s, "\n  children:");
 	    s = fib_node_children_format(path->fp_node.fn_children, s);
 	    vlib_cli_output (vm, "%s", s);
 	    vec_free(s);