From bc10975adbb0aef772496f334dd0bbd23251c1d8 Mon Sep 17 00:00:00 2001
From: Maria Matejka <mq@ucw.cz>
Date: Sun, 15 Oct 2023 23:52:46 +0200
Subject: ASPA: checks done in filters; no autoreload yet

---
 nest/config.Y   |  1 +
 nest/route.h    |  7 +++++
 nest/rt-table.c | 89 +++++++++++++++++++++++++++++++++++++++++++++++++++++++++
 3 files changed, 97 insertions(+)

(limited to 'nest')

diff --git a/nest/config.Y b/nest/config.Y
index 5d2f8d99..594ab3fc 100644
--- a/nest/config.Y
+++ b/nest/config.Y
@@ -139,6 +139,7 @@ CF_ENUM(T_ENUM_RTS, RTS_, STATIC, INHERIT, DEVICE, STATIC_DEVICE, REDIRECT,
 CF_ENUM(T_ENUM_SCOPE, SCOPE_, HOST, LINK, SITE, ORGANIZATION, UNIVERSE, UNDEFINED)
 CF_ENUM(T_ENUM_RTD, RTD_, UNICAST, BLACKHOLE, UNREACHABLE, PROHIBIT)
 CF_ENUM(T_ENUM_ROA, ROA_, UNKNOWN, VALID, INVALID)
+CF_ENUM(T_ENUM_ASPA, ASPA_, UNKNOWN, VALID, INVALID)
 CF_ENUM_PX(T_ENUM_AF, AF_, AFI_, IPV4, IPV6)
 CF_ENUM(T_ENUM_MPLS_POLICY, MPLS_POLICY_, NONE, STATIC, PREFIX, AGGREGATE, VRF)
 
diff --git a/nest/route.h b/nest/route.h
index 9140b9e1..a17ae696 100644
--- a/nest/route.h
+++ b/nest/route.h
@@ -15,6 +15,7 @@
 #include "lib/net.h"
 
 struct ea_list;
+struct adata;
 struct protocol;
 struct proto;
 struct rte_src;
@@ -320,6 +321,7 @@ static inline net *net_get(rtable *tab, const net_addr *addr) { return (net *) f
 net *net_get(rtable *tab, const net_addr *addr);
 net *net_route(rtable *tab, const net_addr *n);
 int net_roa_check(rtable *tab, const net_addr *n, u32 asn);
+int aspa_check(rtable *tab, const struct adata *path);
 rte *rte_find(net *net, struct rte_src *src);
 rte *rte_get_temp(struct rta *, struct rte_src *src);
 void rte_update2(struct channel *c, const net_addr *n, rte *new, struct rte_src *src);
@@ -781,4 +783,9 @@ int rt_flowspec_check(rtable *tab_ip, rtable *tab_flow, const net_addr *n, rta *
 #define ROA_VALID	1
 #define ROA_INVALID	2
 
+#define ASPA_UNKNOWN	0
+#define ASPA_VALID	1
+#define ASPA_INVALID	2
+#define ASPA_CONTAINS_CONFED  3
+
 #endif
diff --git a/nest/rt-table.c b/nest/rt-table.c
index 1b30e7dc..2b930914 100644
--- a/nest/rt-table.c
+++ b/nest/rt-table.c
@@ -346,6 +346,95 @@ net_roa_check(rtable *tab, const net_addr *n, u32 asn)
 #undef FW
 }
 
+/**
+ * aspa_check - check validity of AS Path in an ASPA table
+ * @tab: ASPA table
+ * @path: AS Path to check
+ *
+ * Implements draft-ietf-sidrops-aspa-verification-16.
+ */
+int aspa_check(rtable *tab, const adata *path)
+{
+  struct lp_state lps;
+  lp_save(tmp_linpool, &lps);
+
+  /* No support for confed paths */
+  if (as_path_contains_confed(path))
+    return ASPA_CONTAINS_CONFED;
+
+  /* Normalize the AS Path: drop stuffings */
+  uint len = as_path_getlen(path);
+  u32 *asns = alloca(sizeof(u32) * len);
+  uint ppos = 0;
+  int nsz = 0;
+  while (as_path_walk(path, &ppos, &asns[nsz]))
+    if ((nsz == 0) || (asns[nsz] != asns[nsz-1]))
+      nsz++;
+
+  /* Find the provider blocks for every AS on the path
+   * and check allowed directions */
+  bool *up = alloca(sizeof(bool) * nsz);
+  bool *down = alloca(sizeof(bool) * nsz);
+  bool unknown_flag = false;
+
+  for (int ap=0; ap<nsz; ap++)
+  {
+    net_addr_union nau = { .aspa = NET_ADDR_ASPA(asns[ap]), };
+    net *n = net_find(tab, &nau.n);
+    if (!n || !n->routes)
+    {
+      /* No ASPA for this ASN, therefore UNKNOWN */
+      unknown_flag = up[ap] = down[ap] = true;
+      continue;
+    }
+
+    up[ap] = down[ap] = false;
+
+    for (rte *e = n->routes; e; e = e->next)
+    {
+      if (!rte_is_valid(e))
+	continue;
+
+      eattr *ea = ea_find(e->attrs->eattrs, EA_ASPA_PROVIDERS);
+      if (!ea)
+	continue;
+
+      for (uint i=0; i * sizeof(u32) < ea->u.ptr->length; i++)
+      {
+	if ((ap > 0) && ((u32 *) ea->u.ptr->data)[i] == asns[ap-1])
+	  down[ap] = true;
+	if ((ap + 1 < nsz) && ((u32 *) ea->u.ptr->data)[i] == asns[ap+1])
+	  up[ap] = true;
+
+	if (down[ap] || up[ap])
+	  goto peering_found;
+      }
+    }
+peering_found:;
+  }
+
+  /* Check whether the topology is first ramp up and then ramp down. */
+  int up_end = 0;
+  while (up_end < nsz && up[up_end])
+    up_end++;
+
+  int down_end = nsz - 1;
+  while (down_end > 0 && down[down_end])
+    down_end--;
+
+  /* A significant overlap of obvious unknowns or misconfigured ASPAs. */
+  if (up_end - down_end >= 2)
+    return ASPA_UNKNOWN;
+
+  /* The path has either a single transit provider, or a peering pair on top */
+  else if (up_end - down_end >= 0)
+    return unknown_flag ? ASPA_UNKNOWN : ASPA_VALID;
+
+  /* There is a gap between valid ramp up and valid ramp down */
+  else
+    return ASPA_INVALID;
+}
+
 /**
  * rte_find - find a route
  * @net: network node
-- 
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