Better handling of AS4 optional attribute errors

AS4 optional attribute errors were handled by session
drop (according to BGP RFC). This patch implements
error handling according to new BGP AS4 draft (*)
 - ignoring invalid AS4 optional attributes.

(*) http://www.ietf.org/internet-drafts/draft-chen-rfc4893bis-02.txt

nest/attrs.h

@@ -13,6 +13,8 @@
 
 #define AS_PATH_SET		1	/* Types of path segments */
 #define AS_PATH_SEQUENCE	2
+#define AS_PATH_CONFED_SEQUENCE	3
+#define AS_PATH_CONFED_SET	4
 
 #define AS_PATH_MAXLEN		10000
 

proto/bgp/attrs.c

@@ -76,16 +76,6 @@ bgp_check_as_path(struct bgp_proto *p, byte *a, int len)
   return bgp_check_path(a, len, p->as4_session ? 4 : 2, 11);
 }
 
-static int
-bgp_check_as4_path(struct bgp_proto *p, byte *a, int len)
-{
-  if (bgp_as4_support && (! p->as4_session))
-    return bgp_check_path(a, len, 4, 9);
-  else 
-    return 0;
-}
-
-
 static int
 bgp_check_next_hop(struct bgp_proto *p UNUSED, byte *a, int len)
 {
@@ -196,8 +186,8 @@ static struct attr_desc bgp_attr_table[] = {
     bgp_check_unreach_nlri, NULL },
   { NULL, },									/* BA_EXTENDED_COMM */
   { "as4_path", -1, BAF_OPTIONAL | BAF_TRANSITIVE, EAF_TYPE_OPAQUE, 1,		/* BA_AS4_PATH */
-    bgp_check_as4_path, NULL },
-  { "as4_aggregator", 8, BAF_OPTIONAL | BAF_TRANSITIVE, EAF_TYPE_OPAQUE, 1,	/* BA_AS4_PATH */
+    NULL, NULL },
+  { "as4_aggregator", -1, BAF_OPTIONAL | BAF_TRANSITIVE, EAF_TYPE_OPAQUE, 1,	/* BA_AS4_PATH */
     NULL, NULL }
 };
 
@@ -1063,6 +1053,85 @@ bgp_merge_as_paths(struct adata *old2, struct adata *old4, int req_as, struct li
   return newa;
 }
 
+static int
+as4_aggregator_valid(struct adata *aggr)
+{
+  if (aggr->length != 8)
+    return 0;
+
+  u32 *a = (u32 *) aggr->data;
+
+  if ((a[0] == 0) || (a[1] == 0))
+    return 0;
+}
+
+static int
+as4_path_sanitize_and_get_length(struct adata *path)
+{
+  int res = 0;
+  u8 *p, *dst;
+  int len, plen, copy;
+
+  dst = p = path->data;
+  len = path->length;
+
+  while (len)
+    {
+      if (len <= 2) /* We do not allow empty segments */
+	goto inconsistent_path;
+
+      switch (p[0])
+	{
+	case AS_PATH_SET:
+	  plen = 2 + 4 * p[1];
+	  copy = 1;
+	  res++;
+	  break;
+
+	case AS_PATH_SEQUENCE:
+	  plen = 2 + 4 * p[1];
+	  copy = 1;
+	  res += p[1];
+	  break;
+
+	case AS_PATH_CONFED_SEQUENCE:
+	case AS_PATH_CONFED_SET:
+	  log(L_WARN "BGP: AS4_PATH attribute contains AS_CONFED_* segment, skipping segment");
+	  plen = 2 + 4 * p[1];
+	  copy = 0;
+	  break;
+
+	default:
+	  goto unknown_segment;
+	}
+
+      if (len < plen)
+	goto inconsistent_path;
+
+      if (copy)
+	{
+	  if (dst != p)
+	    memmove(dst, p, plen);
+	  dst += plen;
+	}
+
+      len -= plen;
+      p += plen;
+    }
+
+  path->length = dst - path->data;
+  return res;
+
+ inconsistent_path:
+  log(L_WARN "BGP: AS4_PATH attribute is inconsistent, skipping attribute");
+  return -1;
+
+ unknown_segment:
+  log(L_WARN "BGP: AS4_PATH attribute contains unknown segment, skipping attribute");
+  return -1;
+}
+
+
 
 /* Reconstruct 4B AS_PATH and AGGREGATOR according to RFC 4893 4.2.3 */
 static void
@@ -1072,6 +1141,14 @@ bgp_reconstruct_4b_atts(struct bgp_proto *p, rta *a, struct linpool *pool)
   eattr *p4 =ea_find(a->eattrs, EA_CODE(EAP_BGP, BA_AS4_PATH));
   eattr *a2 =ea_find(a->eattrs, EA_CODE(EAP_BGP, BA_AGGREGATOR));
   eattr *a4 =ea_find(a->eattrs, EA_CODE(EAP_BGP, BA_AS4_AGGREGATOR));
+  int a4_removed = 0;
+
+  if (a4 && !as4_aggregator_valid(a4->u.ptr))
+    {
+      log(L_WARN "BGP: AS4_AGGREGATOR attribute is invalid, skipping attribute");
+      a4 = NULL;
+      a4_removed = 1;
+    }
 
   if (a2)
     {
@@ -1103,7 +1180,7 @@ bgp_reconstruct_4b_atts(struct bgp_proto *p, rta *a, struct linpool *pool)
 	  /* Common case, use old AGGREGATOR attribute */
 	  a2->u.ptr = bgp_aggregator_convert_to_new(a2->u.ptr, pool);
 
-	  if (a2_as == AS_TRANS)
+	  if ((a2_as == AS_TRANS) && !a4_removed)
 	    log(L_WARN "BGP: AGGREGATOR attribute contain AS_TRANS, but AS4_AGGREGATOR is missing");
 	}
     }
@@ -1112,13 +1189,12 @@ bgp_reconstruct_4b_atts(struct bgp_proto *p, rta *a, struct linpool *pool)
       log(L_WARN "BGP: AS4_AGGREGATOR attribute received, but AGGREGATOR attribute is missing");
 
   int p2_len = as_path_getlen(p2->u.ptr);
-  int p4_len = p4 ? as_path_getlen(p4->u.ptr) : AS_PATH_MAXLEN;
+  int p4_len = p4 ? as4_path_sanitize_and_get_length(p4->u.ptr) : -1;
 
-  if (p2_len < p4_len)
+  if ((p4_len <= 0) || (p2_len < p4_len))
     p2->u.ptr = bgp_merge_as_paths(p2->u.ptr, NULL, AS_PATH_MAXLEN, pool);
   else
     p2->u.ptr = bgp_merge_as_paths(p2->u.ptr, p4->u.ptr, p2_len - p4_len, pool);
-
 }
 
 static void

proto/bgp/bgp.c

@@ -53,7 +53,7 @@
  * Unknown transitive attributes are attached to the route as %EAF_TYPE_OPAQUE byte streams.
  */
 
-#define LOCAL_DEBUG
+#undef LOCAL_DEBUG
 
 #include "nest/bird.h"
 #include "nest/iface.h"