VPP-143: Correctly drop local l2tp packets when no session is found

When receiving a local ipv6 packet containing an l2tp packet not associated
with any session, l2tp node was handling the packet as if provided by an ipv6 feature,
hence crashing.

This patch fixes the issue by correctly dropping the packet instead.

This patch also fixes a typo from commit d65346098daf896.

Change-Id: I1b377fc5685568c16831920227671feffac64287
Signed-off-by: Pierre Pfister <ppfister@cisco.com>

vnet/vnet/l2tp/decap.c

@@ -26,7 +26,8 @@
 #define foreach_l2t_decap_error                                   \
 _(USER_TO_NETWORK, "L2TP user (ip6) to L2 network pkts")        \
 _(SESSION_ID_MISMATCH, "l2tpv3 local session id mismatches")    \
-_(COOKIE_MISMATCH, "l2tpv3 local cookie mismatches")  
+_(COOKIE_MISMATCH, "l2tpv3 local cookie mismatches")            \
+_(NO_SESSION, "l2tpv3 session not found")
 
 static char * l2t_decap_error_strings[] = {
 #define _(sym,string) string,
@@ -114,7 +115,7 @@ static inline u32 last_stage (vlib_main_t *vm, vlib_node_runtime_t *node,
     vlib_buffer_t *b = vlib_get_buffer (vm, bi);
     l2t_main_t *lm = &l2t_main;
     ip6_header_t * ip6 = vlib_buffer_get_current (b);
-    vlib_node_t *n = vlib_get_node (vm, l2t_decap_node.index);
+    vlib_node_t *n = vlib_get_node (vm, node->node_index);
     u32 node_counter_base_index = n->error_heap_index;
     vlib_error_main_t * em = &vm->error_main;
     l2tpv3_header_t * l2tp;
@@ -122,6 +123,7 @@ static inline u32 last_stage (vlib_main_t *vm, vlib_node_runtime_t *node,
     l2t_session_t * session;
     u32 session_index;
     u32 next_index;
+    u8 l2tp_decap_local = (l2t_decap_local_node.index == n->index);
     
     /* Other-than-output pkt? We're done... */
     if (vnet_buffer(b)->l2t.next_index != L2T_DECAP_NEXT_L2_INPUT) {
@@ -191,16 +193,22 @@ static inline u32 last_stage (vlib_main_t *vm, vlib_node_runtime_t *node,
 
  done:
    if (next_index == L2T_DECAP_NEXT_NO_INTERCEPT) {
-      // Go to next node on the ip6 configuration chain
-      ip6_main_t * im = &ip6_main;
-      ip_lookup_main_t * lm = &im->lookup_main;
-      ip_config_main_t * cm = &lm->rx_config_mains[VNET_UNICAST];
-      ip6_l2tpv3_config_t * c0;
+       // Small behavioral change between l2tp-decap and l2tp-decap-local
+       if (l2tp_decap_local) {
+	   b->error = node->errors[L2T_DECAP_ERROR_NO_SESSION];
+	   next_index = L2T_DECAP_NEXT_DROP;
+       } else {
+	   // Go to next node on the ip6 configuration chain
+	   ip6_main_t * im = &ip6_main;
+	   ip_lookup_main_t * lm = &im->lookup_main;
+	   ip_config_main_t * cm = &lm->rx_config_mains[VNET_UNICAST];
+	   ip6_l2tpv3_config_t * c0;
 
-      vnet_get_config_data (&cm->config_main,
-                            &b->current_config_index,
-                            &next_index,
-                            sizeof (c0[0]));
+	   vnet_get_config_data (&cm->config_main,
+				 &b->current_config_index,
+				 &next_index,
+				 sizeof (c0[0]));
+       }
     }
 
     if (PREDICT_FALSE(b->flags & VLIB_BUFFER_IS_TRACED)) {
@@ -228,6 +236,12 @@ static uword l2t_decap_node_fn (vlib_main_t * vm,
     return dispatch_pipeline (vm, node, frame);
 }
 
+/*
+ * l2tp-decap and l2tp-decap-local have very slightly different behavior.
+ * When a packet has no associated session l2tp-decap let it go to ip6 forward,
+ * while l2tp-decap-local drops it.
+ */
+
 VLIB_REGISTER_NODE (l2t_decap_node) = {
   .function = l2t_decap_node_fn,
   .name = "l2tp-decap",
@@ -249,7 +263,26 @@ VLIB_REGISTER_NODE (l2t_decap_node) = {
 
 VLIB_NODE_FUNCTION_MULTIARCH (l2t_decap_node, l2t_decap_node_fn)
 
+VLIB_REGISTER_NODE (l2t_decap_local_node) = {
+  .function = l2t_decap_node_fn,
+  .name = "l2tp-decap-local",
+  .vector_size = sizeof (u32),
+  .format_trace = format_l2t_trace,
+  .type = VLIB_NODE_TYPE_INTERNAL,
+
+  .n_errors = ARRAY_LEN(l2t_decap_error_strings),
+  .error_strings = l2t_decap_error_strings,
+
+  .n_next_nodes = L2T_DECAP_N_NEXT,
+
+  /* edit / add dispositions here */
+  .next_nodes = {
+        [L2T_DECAP_NEXT_L2_INPUT] = "l2-input",
+        [L2T_DECAP_NEXT_DROP] = "error-drop",
+  },
+};
+
 void l2tp_decap_init (void) 
 {
-  ip6_register_protocol (IP_PROTOCOL_L2TP, l2t_decap_node.index);
+  ip6_register_protocol (IP_PROTOCOL_L2TP, l2t_decap_local_node.index);
 }

vnet/vnet/l2tp/l2tp.c

@@ -582,7 +582,7 @@ int l2tpv3_interface_enable_disable (vnet_main_t * vnm,
   if (pool_is_free_index (vnm->interface_main.sw_interfaces, sw_if_index))
     return VNET_API_ERROR_INVALID_SW_IF_INDEX;
 
-  feature_index = im->ip6_unicast_rx_feature_ipsec;
+  feature_index = im->ip6_unicast_rx_feature_l2tp_decap;
 
   ci = rx_cm->config_index_by_sw_if_index[sw_if_index];
   ci = (enable_disable

vnet/vnet/l2tp/l2tp.h

@@ -87,6 +87,7 @@ typedef struct {
 l2t_main_t l2t_main;
 extern vlib_node_registration_t l2t_encap_node;
 extern vlib_node_registration_t l2t_decap_node;
+extern vlib_node_registration_t l2t_decap_local_node;
 
 enum {
     SESSION_COUNTER_USER_TO_NETWORK=0,