From 9dbb7eb6ebda016cd14ce8fef403c2b3f7bdd504 Mon Sep 17 00:00:00 2001
From: "Ondrej Zajicek (work)" <santiago@crfreenet.org>
Date: Mon, 24 Jan 2022 03:44:21 +0100
Subject: [PATCH] BGP: Log route updates that were changed to withdraws

Typical BGP error handling is treat-as-withdraw, where an invalid route
is replaced with a withdraw. Log route network when it happens.
---
 proto/bgp/attrs.c   | 4 ++++
 proto/bgp/bgp.h     | 1 +
 proto/bgp/packets.c | 8 +++++++-
 3 files changed, 12 insertions(+), 1 deletion(-)

diff --git a/proto/bgp/attrs.c b/proto/bgp/attrs.c
index 24ba00ba..0688c7cd 100644
--- a/proto/bgp/attrs.c
+++ b/proto/bgp/attrs.c
@@ -1845,6 +1845,10 @@ bgp_rt_notify(struct proto *P, struct channel *C, net *n, rte *new, rte *old)
   {
     struct ea_list *attrs = bgp_update_attrs(p, c, new, new->attrs->eattrs, bgp_linpool2);
 
+    /* Error during attribute processing */
+    if (!attrs)
+      log(L_ERR "%s: Invalid route %N withdrawn", p->p.name, n->n.addr);
+
     /* If attributes are invalid, we fail back to withdraw */
     buck = attrs ? bgp_get_bucket(c, attrs) : bgp_get_withdraw_bucket(c);
     path = new->attrs->src->global_id;
diff --git a/proto/bgp/bgp.h b/proto/bgp/bgp.h
index 5e025ccd..db05b693 100644
--- a/proto/bgp/bgp.h
+++ b/proto/bgp/bgp.h
@@ -423,6 +423,7 @@ struct bgp_parse_state {
   int as4_session;
   int add_path;
   int mpls;
+  int reach_nlri_step;
 
   u32 attrs_seen[256/32];
 
diff --git a/proto/bgp/packets.c b/proto/bgp/packets.c
index 99b5d5b4..9843a9e0 100644
--- a/proto/bgp/packets.c
+++ b/proto/bgp/packets.c
@@ -1335,7 +1335,7 @@ bgp_update_next_hop_none(struct bgp_export_state *s, eattr *a, ea_list **to)
  */
 
 static void
-bgp_rte_update(struct bgp_parse_state *s, net_addr *n, u32 path_id, rta *a0)
+bgp_rte_update(struct bgp_parse_state *s, const net_addr *n, u32 path_id, rta *a0)
 {
   if (path_id != s->last_id)
   {
@@ -1348,6 +1348,10 @@ bgp_rte_update(struct bgp_parse_state *s, net_addr *n, u32 path_id, rta *a0)
 
   if (!a0)
   {
+    /* Route update was changed to withdraw */
+    if (s->err_withdraw && s->reach_nlri_step)
+      REPORT("Invalid route %N withdrawn", n);
+
     /* Route withdraw */
     rte_update3(&s->channel->c, n, NULL, s->last_src);
     return;
@@ -2543,6 +2547,8 @@ bgp_rx_update(struct bgp_conn *conn, byte *pkt, uint len)
   if (s.mp_unreach_len)
     bgp_decode_nlri(&s, s.mp_unreach_af, s.mp_unreach_nlri, s.mp_unreach_len, NULL, NULL, 0);
 
+  s.reach_nlri_step = 1;
+
   if (s.ip_reach_len)
     bgp_decode_nlri(&s, BGP_AF_IPV4, s.ip_reach_nlri, s.ip_reach_len,
 		    ea, s.ip_next_hop_data, s.ip_next_hop_len);