hs-v2: Lookup intro failure cache when picking an intro from descriptor

When picking an intro point from the service descriptor, the client failed to
lookup the failure cache.

It made an HS v2 client re-pick bad intro points for which we already know it
won't work in the first place.

Based on Neel Chauhan original patch.

Fixes #25568

Signed-off-by: David Goulet <dgoulet@torproject.org>

1 files changed, 15 insertions, 4 deletions

diff --git a/src/feature/rend/rendclient.c b/src/feature/rend/rendclient.c
index 2540066dfc..bc94c88efb 100644
--- a/src/feature/rend/rendclient.c
+++ b/src/feature/rend/rendclient.c
@@ -1048,18 +1048,29 @@ rend_client_get_random_intro_impl(const rend_cache_entry_t *entry,
   const or_options_t *options = get_options();
   smartlist_t *usable_nodes;
   int n_excluded = 0;
+  char service_id[REND_SERVICE_ID_LEN_BASE32 + 1];
 
   /* We'll keep a separate list of the usable nodes.  If this becomes empty,
    * no nodes are usable.  */
   usable_nodes = smartlist_new();
   smartlist_add_all(usable_nodes, entry->parsed->intro_nodes);
 
+  /* Get service ID so we can use it to query the failure cache. If we fail to
+   * parse it, this cache entry is no good. */
+  if (BUG(rend_get_service_id(entry->parsed->pk, service_id) < 0)) {
+    return NULL;
+  }
+
   /* Remove the intro points that have timed out during this HS
    * connection attempt from our list of usable nodes. */
-  SMARTLIST_FOREACH(usable_nodes, rend_intro_point_t *, ip,
-                    if (ip->timed_out) {
-                      SMARTLIST_DEL_CURRENT(usable_nodes, ip);
-                    });
+  SMARTLIST_FOREACH_BEGIN(usable_nodes, const rend_intro_point_t *, ip) {
+    bool failed_intro =
+      rend_cache_intro_failure_exists(service_id,
+                       (const uint8_t *) ip->extend_info->identity_digest);
+    if (ip->timed_out || failed_intro) {
+      SMARTLIST_DEL_CURRENT(usable_nodes, ip);
+    };
+  } SMARTLIST_FOREACH_END(ip);
 
  again:
   if (smartlist_len(usable_nodes) == 0) {