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, 61 insertions, 0 deletions

diff --git a/test/test_gre.py b/test/test_gre.py
index eed3d8b2c6f..dd7b8bc6b8f 100644
--- a/test/test_gre.py
+++ b/test/test_gre.py
@@ -867,6 +867,67 @@ class TestGRE(VppTestCase):
         route_tun1_dst.add_vpp_config()
         route_tun2_dst.add_vpp_config()
 
+    def test_gre_loop(self):
+        """ GRE tunnel loop Tests """
+
+        #
+        # Create an L3 GRE tunnel.
+        #  - set it admin up
+        #  - assign an IP Addres
+        #
+        gre_if = VppGreInterface(self,
+                                 self.pg0.local_ip4,
+                                 "1.1.1.2")
+        gre_if.add_vpp_config()
+        gre_if.admin_up()
+        gre_if.config_ip4()
+
+        #
+        # add a route to the tunnel's destination that points
+        # through the tunnel, hence forming a loop in the forwarding
+        # graph
+        #
+        route_dst = VppIpRoute(self, "1.1.1.2", 32,
+                               [VppRoutePath("0.0.0.0",
+                                             gre_if.sw_if_index)])
+        route_dst.add_vpp_config()
+
+        #
+        # packets to the tunnels destination should be dropped
+        #
+        tx = self.create_stream_ip4(self.pg0, "1.1.1.1", "1.1.1.2")
+        self.send_and_assert_no_replies(self.pg2, tx)
+
+        self.logger.info(self.vapi.ppcli("sh adj 7"))
+
+        #
+        # break the loop
+        #
+        route_dst.modify([VppRoutePath(self.pg1.remote_ip4,
+                                       self.pg1.sw_if_index)])
+        route_dst.add_vpp_config()
+
+        rx = self.send_and_expect(self.pg0, tx, self.pg1)
+
+        #
+        # a good route throught the tunnel to check it restacked
+        #
+        route_via_tun_2 = VppIpRoute(self, "2.2.2.2", 32,
+                                     [VppRoutePath("0.0.0.0",
+                                                   gre_if.sw_if_index)])
+        route_via_tun_2.add_vpp_config()
+
+        tx = self.create_stream_ip4(self.pg0, "2.2.2.3", "2.2.2.2")
+        rx = self.send_and_expect(self.pg0, tx, self.pg1)
+        self.verify_tunneled_4o4(self.pg1, rx, tx,
+                                 self.pg0.local_ip4, "1.1.1.2")
+
+        #
+        # cleanup
+        #
+        route_via_tun_2.remove_vpp_config()
+        gre_if.remove_vpp_config()
+
 
 if __name__ == '__main__':
     unittest.main(testRunner=VppTestRunner)