Fix FIB recursion loops via cover (VPP-842)

Change-Id: Ia91c3e8cb27b9e4c1cccefc0a4857dd9995450ab
Signed-off-by: Neale Ranns <nranns@cisco.com>

3 files changed, 81 insertions, 38 deletions

diff --git a/src/vnet/fib/fib_entry_src_rr.c b/src/vnet/fib/fib_entry_src_rr.c
index c145aaa2915..d66ef7b1108 100644
--- a/src/vnet/fib/fib_entry_src_rr.c
+++ b/src/vnet/fib/fib_entry_src_rr.c
@@ -69,6 +69,47 @@ fib_entry_src_rr_init (fib_entry_src_t *src)
     src->rr.fesr_sibling = FIB_NODE_INDEX_INVALID;
 }
 
+
+/*
+ * use the path-list of the cover, unless it would form a loop.
+ * that is unless the cover is via this entry.
+ * If a loop were to form it would be a 1 level loop (i.e. X via X),
+ * and there would be 2 locks on the path-list; one since its used
+ * by the cover, and 1 from here. The first lock will go when the
+ * cover is removed, the second, and last, when the covered walk
+ * occurs during the cover's removel - this is not a place where
+ * we can handle last lock gone.
+ * In short, don't let the loop form. The usual rules of 'we must
+ * let it form so we know when it breaks' don't apply here, since
+ * the loop will break when the cover changes, and this function
+ * will be called again when that happens.
+ */
+static void
+fib_entry_src_rr_use_covers_pl (fib_entry_src_t *src,
+                                const fib_entry_t *fib_entry,
+                                const fib_entry_t *cover)
+{
+    fib_node_index_t *entries = NULL;
+    fib_protocol_t proto;
+
+    proto = fib_entry->fe_prefix.fp_proto;
+    vec_add1(entries, fib_entry_get_index(fib_entry));
+
+    if (fib_path_list_recursive_loop_detect(cover->fe_parent,
+                                            &entries))
+    {
+        src->fes_pl = fib_path_list_create_special(
+            proto,
+            FIB_PATH_LIST_FLAG_DROP,
+            drop_dpo_get(fib_proto_to_dpo(proto)));
+    }
+    else
+    {
+        src->fes_pl = cover->fe_parent;
+    }
+    vec_free(entries);
+}
+
 /*
  * Source activation. Called when the source is the new best source on the entry
  */
@@ -112,40 +153,7 @@ fib_entry_src_rr_activate (fib_entry_src_t *src,
     }
     else
     {
-        /*
-         * use the path-list of the cover, unless it would form a loop.
-         * that is unless the cover is via this entry.
-         * If a loop were to form it would be a 1 level loop (i.e. X via X),
-         * and there would be 2 locks on the path-list; one since its used
-         * by the cover, and 1 from here. The first lock will go when the
-         * cover is removed, the second, and last, when the covered walk
-         * occurs during the cover's removel - this is not a place where
-         * we can handle last lock gone.
-         * In short, don't let the loop form. The usual rules of 'we must
-         * let it form so we know when it breaks' don't apply here, since
-         * the loop will break when the cover changes, and this function
-         * will be called again when that happens.
-         */
-        fib_node_index_t *entries = NULL;
-        fib_protocol_t proto;
-
-        proto = fib_entry->fe_prefix.fp_proto;
-        vec_add1(entries, fib_entry_get_index(fib_entry));
-
-        if (fib_path_list_recursive_loop_detect(cover->fe_parent,
-                                                &entries))
-        {
-            src->fes_pl = fib_path_list_create_special(
-                              proto,
-                              FIB_PATH_LIST_FLAG_DROP,
-                              drop_dpo_get(fib_proto_to_dpo(proto)));
-        }
-        else
-        {
-            src->fes_pl = cover->fe_parent;
-        }
-        vec_free(entries);
-
+        fib_entry_src_rr_use_covers_pl(src, fib_entry, cover);
     }
     fib_path_list_lock(src->fes_pl);
 
@@ -256,7 +264,7 @@ fib_entry_src_rr_cover_update (fib_entry_src_t *src,
     }
     else
     {
-	src->fes_pl = cover->fe_parent;
+        fib_entry_src_rr_use_covers_pl(src, fib_entry, cover);
     }
     fib_path_list_lock(src->fes_pl);
     fib_path_list_unlock(old_path_list);
diff --git a/src/vnet/fib/fib_path.c b/src/vnet/fib/fib_path.c
index 889317fd83c..b47d51f8d51 100644
--- a/src/vnet/fib/fib_path.c
+++ b/src/vnet/fib/fib_path.c
@@ -1716,7 +1716,11 @@ fib_path_get_resolving_interface (fib_node_index_t path_index)
     case FIB_PATH_TYPE_RECEIVE:
 	return (path->receive.fp_interface);
     case FIB_PATH_TYPE_RECURSIVE:
-	return (fib_entry_get_resolving_interface(path->fp_via_fib));    
+        if (fib_path_is_resolved(path_index))
+        {
+            return (fib_entry_get_resolving_interface(path->fp_via_fib));
+        }
+        break;
     case FIB_PATH_TYPE_INTF_RX:
     case FIB_PATH_TYPE_SPECIAL:
     case FIB_PATH_TYPE_DEAG:
@@ -1781,11 +1785,12 @@ fib_path_contribute_urpf (fib_node_index_t path_index,
 	break;
 
     case FIB_PATH_TYPE_RECURSIVE:
-        if (FIB_NODE_INDEX_INVALID != path->fp_via_fib)
+        if (FIB_NODE_INDEX_INVALID != path->fp_via_fib &&
+	    !fib_path_is_looped(path_index))
         {
             /*
              * there's unresolved due to constraints, and there's unresolved
-             * due to ain't go no via. can't do nowt w'out via.
+             * due to ain't got no via. can't do nowt w'out via.
              */
             fib_entry_contribute_urpf(path->fp_via_fib, urpf);
         }
diff --git a/src/vnet/fib/fib_test.c b/src/vnet/fib/fib_test.c
index ddea6b86e7e..486e5616798 100644
--- a/src/vnet/fib/fib_test.c
+++ b/src/vnet/fib/fib_test.c
@@ -2977,6 +2977,36 @@ fib_test_v4 (void)
     	     fib_entry_pool_size());
 
     /*
+     * Make the default route recursive via a unknown next-hop. Thus the
+     * next hop's cover would be the default route
+     */
+    fei = fib_table_entry_path_add(fib_index,
+				   &pfx_0_0_0_0_s_0,
+				   FIB_SOURCE_API,
+				   FIB_ENTRY_FLAG_NONE,
+				   FIB_PROTOCOL_IP4,
+				   &pfx_23_23_23_23_s_32.fp_addr,
+				   ~0, // recursive
+				   fib_index,
+				   1,
+				   NULL,
+				   FIB_ROUTE_PATH_FLAG_NONE);
+    dpo = fib_entry_contribute_ip_forwarding(fei);
+    FIB_TEST(load_balance_is_drop(dpo),
+	     "0.0.0.0.0/0 via is DROP");
+    FIB_TEST((fib_entry_get_resolving_interface(fei) == ~0),
+             "no resolving interface for looped 0.0.0.0/0");
+
+    fei = fib_table_lookup_exact_match(fib_index, &pfx_23_23_23_23_s_32);
+    dpo = fib_entry_contribute_ip_forwarding(fei);
+    FIB_TEST(load_balance_is_drop(dpo),
+	     "23.23.23.23/32 via is DROP");
+    FIB_TEST((fib_entry_get_resolving_interface(fei) == ~0),
+             "no resolving interface for looped 23.23.23.23/32");
+
+    fib_table_entry_delete(fib_index, &pfx_0_0_0_0_s_0, FIB_SOURCE_API);
+
+    /*
      * A recursive route with recursion constraints.
      *  200.200.200.200/32 via 1.1.1.1 is recurse via host constrained
      */