BGP: Implement flowspec validation procedure

Implement flowspec validation procedure as described in RFC 8955 sec. 6
and RFC 9117. The Validation procedure enforces that only routers in the
forwarding path for a network can originate flowspec rules for that
network.

The patch adds new mechanism for tracking inter-table dependencies, which
is necessary as the flowspec validation depends on IP routes, and flowspec
rules must be revalidated when best IP routes change.

The validation procedure is disabled by default and requires that
relevant IP table uses trie, as it uses interval queries for subnets.

5 files changed, 104 insertions, 5 deletions

diff --git a/proto/bgp/attrs.c b/proto/bgp/attrs.c
index 24ba00ba..b28cbd55 100644
--- a/proto/bgp/attrs.c
+++ b/proto/bgp/attrs.c
@@ -1676,6 +1676,10 @@ bgp_preexport(struct proto *P, rte **new, struct linpool *pool UNUSED)
   if (src == NULL)
     return 0;
 
+  /* Reject flowspec that failed validation */
+  if ((e->attrs->dest == RTD_UNREACHABLE) && net_is_flow(e->net->n.addr))
+      return -1;
+
   /* IBGP route reflection, RFC 4456 */
   if (p->is_internal && src->is_internal && (p->local_as == src->local_as))
   {
diff --git a/proto/bgp/bgp.c b/proto/bgp/bgp.c
index e4d754b1..58084136 100644
--- a/proto/bgp/bgp.c
+++ b/proto/bgp/bgp.c
@@ -101,6 +101,7 @@
  * RFC 8203 - BGP Administrative Shutdown Communication
  * RFC 8212 - Default EBGP Route Propagation Behavior without Policies
  * RFC 8654 - Extended Message Support for BGP
+ * RFC 9117 - Revised Validation Procedure for BGP Flow Specifications
  * draft-ietf-idr-ext-opt-param-07
  * draft-uttaro-idr-bgp-persistence-04
  * draft-walton-bgp-hostname-capability-02
@@ -1735,6 +1736,9 @@ bgp_channel_init(struct channel *C, struct channel_config *CF)
 
   if (cf->igp_table_ip6)
     c->igp_table_ip6 = cf->igp_table_ip6->table;
+
+  if (cf->base_table)
+    c->base_table = cf->base_table->table;
 }
 
 static int
@@ -1750,6 +1754,12 @@ bgp_channel_start(struct channel *C)
   if (c->igp_table_ip6)
     rt_lock_table(c->igp_table_ip6);
 
+  if (c->base_table)
+  {
+    rt_lock_table(c->base_table);
+    rt_flowspec_link(c->base_table, c->c.table);
+  }
+
   c->pool = p->p.pool; // XXXX
   bgp_init_bucket_table(c);
   bgp_init_prefix_table(c);
@@ -1834,6 +1844,12 @@ bgp_channel_cleanup(struct channel *C)
   if (c->igp_table_ip6)
     rt_unlock_table(c->igp_table_ip6);
 
+  if (c->base_table)
+  {
+    rt_flowspec_unlink(c->base_table, c->c.table);
+    rt_unlock_table(c->base_table);
+  }
+
   c->index = 0;
 
   /* Cleanup rest of bgp_channel starting at pool field */
@@ -1881,6 +1897,25 @@ bgp_default_igp_table(struct bgp_config *cf, struct bgp_channel_config *cc, u32
   cf_error("Undefined IGP table");
 }
 
+static struct rtable_config *
+bgp_default_base_table(struct bgp_config *cf, struct bgp_channel_config *cc)
+{
+  /* Expected table type */
+  u32 type = (cc->afi == BGP_AF_FLOW4) ? NET_IP4 : NET_IP6;
+
+  /* First, try appropriate IP channel */
+  u32 afi2 = BGP_AF(BGP_AFI(cc->afi), BGP_SAFI_UNICAST);
+  struct bgp_channel_config *cc2 = bgp_find_channel_config(cf, afi2);
+  if (cc2 && (cc2->c.table->addr_type == type))
+    return cc2->c.table;
+
+  /* Last, try default table of given type */
+  struct rtable_config *tab = cf->c.global->def_tables[type];
+  if (tab)
+    return tab;
+
+  cf_error("Undefined base table");
+}
 
 void
 bgp_postconfig(struct proto_config *CF)
@@ -2025,6 +2060,14 @@ bgp_postconfig(struct proto_config *CF)
 	cf_error("Mismatched IGP table type");
     }
 
+    /* Default value of base table */
+    if ((BGP_SAFI(cc->afi) == BGP_SAFI_FLOW) && cc->validate && !cc->base_table)
+      cc->base_table = bgp_default_base_table(cf, cc);
+
+    if (cc->base_table && !cc->base_table->trie_used)
+      cf_error("Flowspec validation requires base table (%s) with trie",
+	       cc->base_table->name);
+
     if (cf->multihop && (cc->gw_mode == GW_DIRECT))
       cf_error("Multihop BGP cannot use direct gateway mode");
 
@@ -2093,7 +2136,7 @@ bgp_reconfigure(struct proto *P, struct proto_config *CF)
   return same;
 }
 
-#define IGP_TABLE(cf, sym) ((cf)->igp_table_##sym ? (cf)->igp_table_##sym ->table : NULL )
+#define TABLE(cf, NAME) ((cf)->NAME ? (cf)->NAME->table : NULL )
 
 static int
 bgp_channel_reconfigure(struct channel *C, struct channel_config *CC, int *import_changed, int *export_changed)
@@ -2104,6 +2147,7 @@ bgp_channel_reconfigure(struct channel *C, struct channel_config *CC, int *impor
   struct bgp_channel_config *old = c->cf;
 
   if ((new->secondary != old->secondary) ||
+      (new->validate != old->validate) ||
       (new->gr_able != old->gr_able) ||
       (new->llgr_able != old->llgr_able) ||
       (new->llgr_time != old->llgr_time) ||
@@ -2111,8 +2155,9 @@ bgp_channel_reconfigure(struct channel *C, struct channel_config *CC, int *impor
       (new->add_path != old->add_path) ||
       (new->import_table != old->import_table) ||
       (new->export_table != old->export_table) ||
-      (IGP_TABLE(new, ip4) != IGP_TABLE(old, ip4)) ||
-      (IGP_TABLE(new, ip6) != IGP_TABLE(old, ip6)))
+      (TABLE(new, igp_table_ip4) != TABLE(old, igp_table_ip4)) ||
+      (TABLE(new, igp_table_ip6) != TABLE(old, igp_table_ip6)) ||
+      (TABLE(new, base_table) != TABLE(old, base_table)))
     return 0;
 
   if (new->mandatory && !old->mandatory && (C->channel_state != CS_UP))
@@ -2526,6 +2571,9 @@ bgp_show_proto_info(struct proto *P)
 
       if (c->igp_table_ip6)
 	cli_msg(-1006, "    IGP IPv6 table: %s", c->igp_table_ip6->name);
+
+      if (c->base_table)
+	cli_msg(-1006, "    Base table:     %s", c->base_table->name);
     }
   }
 }
diff --git a/proto/bgp/bgp.h b/proto/bgp/bgp.h
index cca4b448..e894d632 100644
--- a/proto/bgp/bgp.h
+++ b/proto/bgp/bgp.h
@@ -146,6 +146,7 @@ struct bgp_channel_config {
   u8 mandatory;				/* Channel is mandatory in capability negotiation */
   u8 gw_mode;				/* How we compute route gateway from next_hop attr, see GW_* */
   u8 secondary;				/* Accept also non-best routes (i.e. RA_ACCEPTED) */
+  u8 validate;				/* Validate Flowspec per RFC 8955 (6) */
   u8 gr_able;				/* Allow full graceful restart for the channel */
   u8 llgr_able;				/* Allow full long-lived GR for the channel */
   uint llgr_time;			/* Long-lived graceful restart stale time */
@@ -159,6 +160,7 @@ struct bgp_channel_config {
 
   struct rtable_config *igp_table_ip4;	/* Table for recursive IPv4 next hop lookups */
   struct rtable_config *igp_table_ip6;	/* Table for recursive IPv6 next hop lookups */
+  struct rtable_config *base_table;	/* Base table for Flowspec validation */
 };
 
 #define BGP_PT_INTERNAL		1
@@ -340,6 +342,7 @@ struct bgp_channel {
 
   rtable *igp_table_ip4;		/* Table for recursive IPv4 next hop lookups */
   rtable *igp_table_ip6;		/* Table for recursive IPv6 next hop lookups */
+  rtable *base_table;			/* Base table for Flowspec validation */
 
   /* Rest are zeroed when down */
   pool *pool;
@@ -449,6 +452,7 @@ struct bgp_parse_state {
   jmp_buf err_jmpbuf;
 
   struct hostentry *hostentry;
+  struct rtable *base_table;
   adata *mpls_labels;
 
   /* Cached state for bgp_rte_update() */
@@ -515,7 +519,7 @@ struct rte_source *bgp_get_source(struct bgp_proto *p, u32 path_id);
 static inline int
 rte_resolvable(rte *rt)
 {
-  return rt->attrs->dest == RTD_UNICAST;
+  return rt->attrs->dest != RTD_UNREACHABLE;
 }
 
 
diff --git a/proto/bgp/config.Y b/proto/bgp/config.Y
index 2dfbdca9..27c352c5 100644
--- a/proto/bgp/config.Y
+++ b/proto/bgp/config.Y
@@ -31,7 +31,7 @@ CF_KEYWORDS(BGP, LOCAL, NEIGHBOR, AS, HOLD, TIME, CONNECT, RETRY, KEEPALIVE,
 	STRICT, BIND, CONFEDERATION, MEMBER, MULTICAST, FLOW4, FLOW6, LONG,
 	LIVED, STALE, IMPORT, IBGP, EBGP, MANDATORY, INTERNAL, EXTERNAL, SETS,
 	DYNAMIC, RANGE, NAME, DIGITS, BGP_AIGP, AIGP, ORIGINATE, COST, ENFORCE,
-	FIRST)
+	FIRST, VALIDATE, BASE)
 
 %type <i> bgp_nh
 %type <i32> bgp_afi
@@ -255,6 +255,11 @@ bgp_channel_item:
  | GATEWAY DIRECT { BGP_CC->gw_mode = GW_DIRECT; }
  | GATEWAY RECURSIVE { BGP_CC->gw_mode = GW_RECURSIVE; }
  | SECONDARY bool { BGP_CC->secondary = $2; }
+ | VALIDATE bool {
+    BGP_CC->validate = $2;
+    if (BGP_SAFI(BGP_CC->afi) != BGP_SAFI_FLOW)
+      cf_error("Validate option limited to flowspec channels");
+   }
  | GRACEFUL RESTART bool { BGP_CC->gr_able = $3; }
  | LONG LIVED GRACEFUL RESTART bool { BGP_CC->llgr_able = $5; }
  | LONG LIVED STALE TIME expr { BGP_CC->llgr_time = $5; }
@@ -278,6 +283,16 @@ bgp_channel_item:
     else
       cf_error("Mismatched IGP table type");
    }
+ | BASE TABLE rtable {
+    if (BGP_SAFI(BGP_CC->afi) != BGP_SAFI_FLOW)
+      cf_error("Base table option limited to flowspec channels");
+
+    if (((BGP_CC->afi == BGP_AF_FLOW4) && ($3->addr_type == NET_IP4)) ||
+        ((BGP_CC->afi == BGP_AF_FLOW6) && ($3->addr_type == NET_IP6)))
+      BGP_CC->base_table = $3;
+    else
+      cf_error("Mismatched base table type");
+   }
  ;
 
 bgp_channel_opts:
diff --git a/proto/bgp/packets.c b/proto/bgp/packets.c
index 99b5d5b4..e536f873 100644
--- a/proto/bgp/packets.c
+++ b/proto/bgp/packets.c
@@ -1009,6 +1009,23 @@ bgp_apply_mpls_labels(struct bgp_parse_state *s, rta *a, u32 *labels, uint lnum)
   }
 }
 
+static void
+bgp_apply_flow_validation(struct bgp_parse_state *s, const net_addr *n, rta *a)
+{
+  struct bgp_channel *c = s->channel;
+  int valid = rt_flowspec_check(c->base_table, c->c.table, n, a, s->proto->is_interior);
+  a->dest = valid ? RTD_NONE : RTD_UNREACHABLE;
+
+  /* Set rte.bgp.base_table later from this state variable */
+  s->base_table = c->base_table;
+
+  /* Invalidate cached rta if dest changes */
+  if (s->cached_rta && (s->cached_rta->dest != a->dest))
+  {
+    rta_free(s->cached_rta);
+    s->cached_rta = NULL;
+  }
+}
 
 static int
 bgp_match_src(struct bgp_export_state *s, int mode)
@@ -1370,6 +1387,7 @@ bgp_rte_update(struct bgp_parse_state *s, net_addr *n, u32 path_id, rta *a0)
   e->pflags = 0;
   e->u.bgp.suppressed = 0;
   e->u.bgp.stale = -1;
+  e->u.bgp.base_table = s->base_table;
   rte_update3(&s->channel->c, n, e, s->last_src);
 }
 
@@ -1884,6 +1902,10 @@ bgp_decode_nlri_flow4(struct bgp_parse_state *s, byte *pos, uint len, rta *a)
     net_fill_flow4(n, px, pxlen, pos, flen);
     ADVANCE(pos, len, flen);
 
+    /* Apply validation procedure per RFC 8955 (6) */
+    if (a && s->channel->cf->validate)
+      bgp_apply_flow_validation(s, n, a);
+
     bgp_rte_update(s, n, path_id, a);
   }
 }
@@ -1972,6 +1994,10 @@ bgp_decode_nlri_flow6(struct bgp_parse_state *s, byte *pos, uint len, rta *a)
     net_fill_flow6(n, px, pxlen, pos, flen);
     ADVANCE(pos, len, flen);
 
+    /* Apply validation procedure per RFC 8955 (6) */
+    if (a && s->channel->cf->validate)
+      bgp_apply_flow_validation(s, n, a);
+
     bgp_rte_update(s, n, path_id, a);
   }
 }
@@ -2425,6 +2451,8 @@ bgp_decode_nlri(struct bgp_parse_state *s, u32 afi, byte *nlri, uint len, ea_lis
   s->last_id = 0;
   s->last_src = s->proto->p.main_source;
 
+  s->base_table = NULL;
+
   /*
    * IPv4 BGP and MP-BGP may be used together in one update, therefore we do not
    * add BA_NEXT_HOP in bgp_decode_attrs(), but we add it here independently for