ospfd: avoid exhausting memory with OSPF vertices (BZ#476)

This was found in scale testing at OSR;  ospfd is adding the same link
over and over again to the SPF tree.  This fix prevents the resulting
memory corruption from happening and adds a debug message to track
occurence of this issue and/or confirm a proper fix.

(This version was improved by Scott Feldman over the earlier RFC.)

* ospfd/ospf_spf.c: (ospf_spf_add_parent) loop over existing vertices
  and refuse to add duplicates.

Tested-by: Martin Winter <mwinter@opensourcerouting.org>
Signed-off-by: Scott Feldman <sfeldma@cumulusnetworks.com>
Signed-off-by: David Lamparter <equinox@opensourcerouting.org>

ospfd/ospf_spf.c

@@ -422,7 +422,8 @@ ospf_spf_add_parent (struct vertex *v, struct vertex *w,
                      struct vertex_nexthop *newhop,
                      unsigned int distance)
 {
-  struct vertex_parent *vp;
+  struct vertex_parent *vp, *wp;
+  struct listnode *node;
 
   /* we must have a newhop, and a distance */
   assert (v && w && newhop);
@@ -456,7 +457,19 @@ ospf_spf_add_parent (struct vertex *v, struct vertex *w,
       w->distance = distance;
     }
 
-  /* new parent is <= existing parents, add it to parent list */  
+  /* new parent is <= existing parents, add it to parent list (if nexthop
+   * not on parent list)
+   */  
+  for (ALL_LIST_ELEMENTS_RO(w->parents, node, wp))
+    {
+      if (memcmp(newhop, wp->nexthop, sizeof(*newhop)) == 0)
+        {
+          if (IS_DEBUG_OSPF_EVENT)
+            zlog_debug ("%s: ... nexthop already on parent list, skipping add", __func__);
+          return;
+        }
+    }
+
   vp = vertex_parent_new (v, ospf_lsa_has_link (w->lsa, v->lsa), newhop);
   listnode_add (w->parents, vp);