From 766fc86df46ff88364610b18e28904c3b45f98f1 Mon Sep 17 00:00:00 2001
From: teor <teor@riseup.net>
Date: Wed, 13 May 2020 13:17:41 +1000
Subject: [PATCH] circuitbuild: Do node checks when choosing exits

And check that the correct flags are passed when choosing exits.

Adds the following checks for exits:
* must support EXTEND2 cells,
* must have an ntor circuit crypto key,
* can't require the guard flag,
* can't be a direct connection.

All these checks are already implied by other code.

Part of 34200.
---
 src/core/or/circuitbuild.c | 48 +++++++++++++++-----------------------
 1 file changed, 19 insertions(+), 29 deletions(-)

diff --git a/src/core/or/circuitbuild.c b/src/core/or/circuitbuild.c
index b840ca7a7d..bac82eb9f5 100644
--- a/src/core/or/circuitbuild.c
+++ b/src/core/or/circuitbuild.c
@@ -1563,7 +1563,23 @@ choose_good_exit_server_general(router_crn_flags_t flags)
   const node_t *selected_node=NULL;
   const int need_uptime = (flags & CRN_NEED_UPTIME) != 0;
   const int need_capacity = (flags & CRN_NEED_CAPACITY) != 0;
-  const int direct_conn = (flags & CRN_DIRECT_CONN) != 0;
+
+  /* We should not require guard flags on exits. */
+  IF_BUG_ONCE(flags & CRN_NEED_GUARD)
+    return NULL;
+
+  /* We reject single-hop exits for all node positions. */
+  IF_BUG_ONCE(flags & CRN_DIRECT_CONN)
+    return NULL;
+
+  /* This isn't the function for picking rendezvous nodes. */
+  IF_BUG_ONCE(flags & CRN_RENDEZVOUS_V3)
+    return NULL;
+
+  /* We only want exits to extend if we cannibalize the circuit.
+   * But we don't require IPv6 extends yet. */
+  IF_BUG_ONCE(flags & CRN_INITIATE_IPV6_EXTEND)
+    return NULL;
 
   connections = get_connection_array();
 
@@ -1596,19 +1612,14 @@ choose_good_exit_server_general(router_crn_flags_t flags)
        */
       continue;
     }
-    if (!node_has_preferred_descriptor(node, direct_conn)) {
+    if (!router_can_choose_node(node, flags)) {
       n_supported[i] = -1;
       continue;
     }
-    if (!node->is_running || node->is_bad_exit) {
+    if (node->is_bad_exit) {
       n_supported[i] = -1;
       continue; /* skip routers that are known to be down or bad exits */
     }
-    if (node_get_purpose(node) != ROUTER_PURPOSE_GENERAL) {
-      /* never pick a non-general node as a random exit. */
-      n_supported[i] = -1;
-      continue;
-    }
     if (routerset_contains_node(options->ExcludeExitNodesUnion_, node)) {
       n_supported[i] = -1;
       continue; /* user asked us not to use it, no matter what */
@@ -1618,27 +1629,6 @@ choose_good_exit_server_general(router_crn_flags_t flags)
       n_supported[i] = -1;
       continue; /* not one of our chosen exit nodes */
     }
-
-    if (node_is_unreliable(node, need_uptime, need_capacity, 0)) {
-      n_supported[i] = -1;
-      continue; /* skip routers that are not suitable.  Don't worry if
-                 * this makes us reject all the possible routers: if so,
-                 * we'll retry later in this function with need_update and
-                 * need_capacity set to 0. */
-    }
-    if (!(node->is_valid)) {
-      /* if it's invalid and we don't want it */
-      n_supported[i] = -1;
-//      log_fn(LOG_DEBUG,"Skipping node %s (index %d) -- invalid router.",
-//             router->nickname, i);
-      continue; /* skip invalid routers */
-    }
-    /* We do not allow relays that allow single hop exits by default. Option
-     * was deprecated in 0.2.9.2-alpha and removed in 0.3.1.0-alpha. */
-    if (node_allows_single_hop_exits(node)) {
-      n_supported[i] = -1;
-      continue;
-    }
     if (node_exit_policy_rejects_all(node)) {
       n_supported[i] = -1;
 //      log_fn(LOG_DEBUG,"Skipping node %s (index %d) -- it rejects all.",