Babel: Rework handling of retractions

An update with wildcard AE and infinite metric should be treated as a
global retraction of all prefixes announced by that neighbour, per
section 4.4.9 of the RFC. In addition, router ID and seqno in retraction
updates should be ignored. This reworks the handling of retractions and
adjusts the parser to handle all this correctly.

Signed-off-by: Toke Høiland-Jørgensen <toke@toke.dk>

2 files changed, 61 insertions, 25 deletions

diff --git a/proto/babel/babel.c b/proto/babel/babel.c
index 8e104d60..8204838b 100644
--- a/proto/babel/babel.c
+++ b/proto/babel/babel.c
@@ -1040,17 +1040,18 @@ babel_handle_update(union babel_msg *m, struct babel_iface *ifa)
   struct babel_proto *p = ifa->proto;
   struct babel_msg_update *msg = &m->update;
 
-  struct babel_neighbor *n;
+  struct babel_neighbor *nbr;
   struct babel_entry *e;
   struct babel_source *s;
   struct babel_route *r;
+  node *n;
   int feasible;
 
   TRACE(D_PACKETS, "Handling update for %I/%d with seqno %d metric %d",
 	msg->prefix, msg->plen, msg->seqno, msg->metric);
 
-  n = babel_find_neighbor(ifa, msg->sender);
-  if (!n)
+  nbr = babel_find_neighbor(ifa, msg->sender);
+  if (!nbr)
   {
     DBG("Babel: Haven't heard from neighbor %I; ignoring update.\n", msg->sender);
     return;
@@ -1095,55 +1096,88 @@ babel_handle_update(union babel_msg *m, struct babel_iface *ifa)
    *   of the Interval value included in the update.
    */
 
+  /* Retraction */
   if (msg->metric == BABEL_INFINITY)
-    e = babel_find_entry(p, msg->prefix, msg->plen);
-  else
-    e = babel_get_entry(p, msg->prefix, msg->plen);
+  {
+    if (msg->ae == BABEL_AE_WILDCARD)
+    {
+      /*
+       * Special case: This is a retraction of all prefixes announced by this
+       * neighbour (see second-to-last paragraph of section 4.4.9 in the RFC).
+       */
+      WALK_LIST(n, nbr->routes)
+      {
+	r = SKIP_BACK(struct babel_route, neigh_route, n);
+	r->metric = BABEL_INFINITY;
+	babel_select_route(r->e);
+      }
+    }
+    else
+    {
+      e = babel_find_entry(p, msg->prefix, msg->plen);
 
-  if (!e)
+      if (!e)
+	return;
+
+      /* The route entry indexed by neighbour */
+      r = babel_find_route(e, nbr);
+
+      if (!r)
+	return;
+
+      r->metric = BABEL_INFINITY;
+      babel_select_route(e);
+    }
+
+    /* Done with retractions */
     return;
+  }
 
+  e = babel_get_entry(p, msg->prefix, msg->plen);
+  r = babel_find_route(e, nbr); /* the route entry indexed by neighbour */
   s = babel_find_source(e, msg->router_id); /* for feasibility */
-  r = babel_find_route(e, n); /* the route entry indexed by neighbour */
   feasible = babel_is_feasible(s, msg->seqno, msg->metric);
 
   if (!r)
   {
-    if (!feasible || (msg->metric == BABEL_INFINITY))
+    if (!feasible)
       return;
 
-    r = babel_get_route(e, n);
+    r = babel_get_route(e, nbr);
     r->advert_metric = msg->metric;
     r->router_id = msg->router_id;
-    r->metric = babel_compute_metric(n, msg->metric);
+    r->metric = babel_compute_metric(nbr, msg->metric);
     r->next_hop = msg->next_hop;
     r->seqno = msg->seqno;
   }
   else if (r == r->e->selected_in && !feasible)
   {
-    /* Route is installed and update is infeasible - we may lose the route, so
-       send a unicast seqno request (section 3.8.2.2 second paragraph). */
+    /*
+     * Route is installed and update is infeasible - we may lose the route,
+     * so send a unicast seqno request (section 3.8.2.2 second paragraph).
+     */
     babel_unicast_seqno_request(r);
 
-    if (msg->router_id == r->router_id) return;
-    r->metric = BABEL_INFINITY; /* retraction */
+    if (msg->router_id == r->router_id)
+      return;
+
+    /* Treat as retraction */
+    r->metric = BABEL_INFINITY;
   }
   else
   {
     /* Last paragraph above - update the entry */
     r->advert_metric = msg->metric;
-    r->metric = babel_compute_metric(n, msg->metric);
-    r->router_id = msg->router_id;
+    r->metric = babel_compute_metric(nbr, msg->metric);
     r->next_hop = msg->next_hop;
+
+    r->router_id = msg->router_id;
     r->seqno = msg->seqno;
 
-    if (msg->metric != BABEL_INFINITY)
-    {
-      r->expiry_interval = BABEL_ROUTE_EXPIRY_FACTOR(msg->interval);
-      r->expires = now + r->expiry_interval;
-      if (r->expiry_interval > BABEL_ROUTE_REFRESH_INTERVAL)
-        r->refresh_time = now + r->expiry_interval - BABEL_ROUTE_REFRESH_INTERVAL;
-    }
+    r->expiry_interval = BABEL_ROUTE_EXPIRY_FACTOR(msg->interval);
+    r->expires = now + r->expiry_interval;
+    if (r->expiry_interval > BABEL_ROUTE_REFRESH_INTERVAL)
+      r->refresh_time = now + r->expiry_interval - BABEL_ROUTE_REFRESH_INTERVAL;
 
     /* If the route is not feasible at this point, it means it is from another
        neighbour than the one currently selected; so send a unicast seqno
diff --git a/proto/babel/packets.c b/proto/babel/packets.c
index be47aa75..d0cc613e 100644
--- a/proto/babel/packets.c
+++ b/proto/babel/packets.c
@@ -480,6 +480,7 @@ babel_read_update(struct babel_tlv *hdr, union babel_msg *m,
     if (tlv->plen > 0)
       return PARSE_ERROR;
 
+    msg->plen = 0;
     msg->prefix = IPA_NONE;
     break;
 
@@ -523,7 +524,8 @@ babel_read_update(struct babel_tlv *hdr, union babel_msg *m,
     return PARSE_IGNORE;
   }
 
-  if (!state->router_id_seen)
+  /* Update must have Router ID, unless it is retraction */
+  if (!state->router_id_seen && (msg->metric != BABEL_INFINITY))
   {
     DBG("Babel: No router ID seen before update\n");
     return PARSE_ERROR;