From c73b5d2d3d94204d2a81d93efd02c4c115859353 Mon Sep 17 00:00:00 2001
From: Eugene Bogomazov <eb@qrator.net>
Date: Mon, 11 Jul 2022 17:19:34 +0200
Subject: BGP: Implement BGP roles

Implement BGP roles as described in RFC 9234. It is  a mechanism for
route leak prevention and automatic route filtering based on common BGP
topology relationships. It defines role capability (controlled by 'local
role' option) and OTC route attribute, which is used for automatic route
filtering and leak detection.

Minor changes done by commiter.
---
 proto/bgp/attrs.c | 69 ++++++++++++++++++++++++++++++++++++++++++++++++++++---
 1 file changed, 66 insertions(+), 3 deletions(-)

(limited to 'proto/bgp/attrs.c')

diff --git a/proto/bgp/attrs.c b/proto/bgp/attrs.c
index 9dd9fb1a..0d2116b7 100644
--- a/proto/bgp/attrs.c
+++ b/proto/bgp/attrs.c
@@ -896,6 +896,18 @@ bgp_decode_large_community(struct bgp_parse_state *s, uint code UNUSED, uint fla
   bgp_set_attr_ptr(to, s->pool, BA_LARGE_COMMUNITY, flags, ad);
 }
 
+
+static void
+bgp_decode_otc(struct bgp_parse_state *s, uint code UNUSED, uint flags, byte *data UNUSED, uint len, ea_list **to)
+{
+  if (len != 4)
+    WITHDRAW(BAD_LENGTH, "OTC", len);
+
+  u32 val = get_u32(data);
+  bgp_set_attr_u32(to, s->pool, BA_ONLY_TO_CUSTOMER, flags, val);
+}
+
+
 static void
 bgp_export_mpls_label_stack(struct bgp_export_state *s, eattr *a)
 {
@@ -1109,6 +1121,13 @@ static const struct bgp_attr_desc bgp_attr_table[] = {
     .encode = bgp_encode_u32s,
     .decode = bgp_decode_large_community,
   },
+  [BA_ONLY_TO_CUSTOMER] = {
+    .name = "otc",
+    .type = EAF_TYPE_INT,
+    .flags = BAF_OPTIONAL | BAF_TRANSITIVE,
+    .encode = bgp_encode_u32,
+    .decode = bgp_decode_otc,
+  },
   [BA_MPLS_LABEL_STACK] = {
     .name = "mpls_label_stack",
     .type = EAF_TYPE_INT_SET,
@@ -1445,6 +1464,29 @@ bgp_finish_attrs(struct bgp_parse_state *s, rta *a)
     REPORT("Discarding AIGP attribute received on non-AIGP session");
     bgp_unset_attr(&a->eattrs, s->pool, BA_AIGP);
   }
+
+  /* Handle OTC ingress procedure, RFC 9234 */
+  if (bgp_channel_is_role_applicable(s->channel))
+  {
+    struct bgp_proto *p = s->proto;
+    eattr *e = bgp_find_attr(a->eattrs, BA_ONLY_TO_CUSTOMER);
+
+    /* Reject routes from downstream if they are leaked */
+    if (e && (p->cf->local_role == BGP_ROLE_PROVIDER ||
+	      p->cf->local_role == BGP_ROLE_RS_SERVER))
+      WITHDRAW("Route leak detected - OTC attribute from downstream");
+
+    /* Reject routes from peers if they are leaked */
+    if (e && (p->cf->local_role == BGP_ROLE_PEER) && (e->u.data != p->cf->remote_as))
+      WITHDRAW("Route leak detected - OTC attribute with mismatched ASN (%u)",
+	       (uint) e->u.data);
+
+    /* Mark routes from upstream if it did not happened before */
+    if (!e && (p->cf->local_role == BGP_ROLE_CUSTOMER ||
+	       p->cf->local_role == BGP_ROLE_PEER ||
+	       p->cf->local_role == BGP_ROLE_RS_CLIENT))
+      bgp_set_attr_u32(&a->eattrs, s->pool, BA_ONLY_TO_CUSTOMER, 0, p->cf->remote_as);
+  }
 }
 
 
@@ -1673,6 +1715,7 @@ bgp_preexport(struct channel *C, rte **new, struct linpool *pool UNUSED)
 {
   rte *e = *new;
   struct proto *SRC = e->attrs->src->proto;
+  struct bgp_channel *c = (struct bgp_channel *) C;
   struct bgp_proto *p = (struct bgp_proto *) C->proto;
   struct bgp_proto *src = (SRC->proto == &proto_bgp) ? (struct bgp_proto *) SRC : NULL;
 
@@ -1702,11 +1745,11 @@ bgp_preexport(struct channel *C, rte **new, struct linpool *pool UNUSED)
   }
 
   /* Handle well-known communities, RFC 1997 */
-  struct eattr *c;
+  struct eattr *a;
   if (p->cf->interpret_communities &&
-      (c = ea_find(e->attrs->eattrs, EA_CODE(PROTOCOL_BGP, BA_COMMUNITY))))
+      (a = bgp_find_attr(e->attrs->eattrs, BA_COMMUNITY)))
   {
-    const struct adata *d = c->u.ptr;
+    const struct adata *d = a->u.ptr;
 
     /* Do not export anywhere */
     if (int_set_contains(d, BGP_COMM_NO_ADVERTISE))
@@ -1725,6 +1768,16 @@ bgp_preexport(struct channel *C, rte **new, struct linpool *pool UNUSED)
       return -1;
   }
 
+  /* Do not export routes marked with OTC to upstream, RFC 9234 */
+  if (bgp_channel_is_role_applicable(c))
+  {
+    a = bgp_find_attr(e->attrs->eattrs, BA_ONLY_TO_CUSTOMER);
+    if (a && (p->cf->local_role==BGP_ROLE_CUSTOMER ||
+	      p->cf->local_role==BGP_ROLE_PEER ||
+	      p->cf->local_role==BGP_ROLE_RS_CLIENT))
+      return -1;
+  }
+
   return 0;
 }
 
@@ -1834,6 +1887,16 @@ bgp_update_attrs(struct bgp_proto *p, struct bgp_channel *c, rte *e, ea_list *at
     }
   }
 
+  /* Mark routes for downstream with OTC, RFC 9234 */
+  if (bgp_channel_is_role_applicable(c))
+  {
+    a = bgp_find_attr(attrs, BA_ONLY_TO_CUSTOMER);
+    if (!a && (p->cf->local_role == BGP_ROLE_PROVIDER ||
+	       p->cf->local_role == BGP_ROLE_PEER ||
+	       p->cf->local_role == BGP_ROLE_RS_SERVER))
+      bgp_set_attr_u32(&attrs, pool, BA_ONLY_TO_CUSTOMER, 0, p->public_as);
+  }
+
   /*
    * Presence of mandatory attributes ORIGIN and AS_PATH is ensured by above
    * conditions. Presence and validity of quasi-mandatory NEXT_HOP attribute
-- 
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