BGP: Make routing loops silent

One of previous commits added error logging of invalid routes. This
also inadvertently caused error logging of route loops, which should
be ignored silently. Fix that.

2 files changed, 9 insertions, 5 deletions

diff --git a/proto/bgp/attrs.c b/proto/bgp/attrs.c
index 968d7d2b..15713b63 100644
--- a/proto/bgp/attrs.c
+++ b/proto/bgp/attrs.c
@@ -1397,19 +1397,19 @@ bgp_decode_attrs(struct bgp_parse_state *s, byte *data, uint len)
 
   /* Reject routes with our ASN in AS_PATH attribute */
   if (bgp_as_path_loopy(p, attrs, p->local_as))
-    goto withdraw;
+    goto loop;
 
   /* Reject routes with our Confederation ID in AS_PATH attribute; RFC 5065 4.0 */
   if ((p->public_as != p->local_as) && bgp_as_path_loopy(p, attrs, p->public_as))
-    goto withdraw;
+    goto loop;
 
   /* Reject routes with our Router ID in ORIGINATOR_ID attribute; RFC 4456 8 */
   if (p->is_internal && bgp_originator_id_loopy(p, attrs))
-    goto withdraw;
+    goto loop;
 
   /* Reject routes with our Cluster ID in CLUSTER_LIST attribute; RFC 4456 8 */
   if (p->rr_client && bgp_cluster_list_loopy(p, attrs))
-    goto withdraw;
+    goto loop;
 
   /* If there is no local preference, define one */
   if (!BIT32_TEST(s->attrs_seen, BA_LOCAL_PREF))
@@ -1430,6 +1430,10 @@ withdraw:
 
   s->err_withdraw = 1;
   return NULL;
+
+loop:
+  /* Loops are handled as withdraws, but ignored silently. Do not set err_withdraw. */
+  return NULL;
 }
 
 void
diff --git a/proto/bgp/packets.c b/proto/bgp/packets.c
index 9d21fd34..21052186 100644
--- a/proto/bgp/packets.c
+++ b/proto/bgp/packets.c
@@ -1422,7 +1422,7 @@ bgp_decode_mpls_labels(struct bgp_parse_state *s, byte **pos, uint *len, uint *p
 
     /* RFC 8277 2.4 - withdraw does not have variable-size MPLS stack but
        fixed-size 24-bit Compatibility field, which MUST be ignored */
-    if (!a && !s->err_withdraw)
+    if (!s->reach_nlri_step)
       return;
   }
   while (!(label & BGP_MPLS_BOS));