guard: Ignore marked for close circuit when changing state to open

When we consider all circuits in "waiting for guard" state to be promoted to
an "open" state, we were considering all circuits, even the one marked for
close.

This ultiamtely triggers a "circuit_has_opened()" called on the circuit that
is marked for close which then leads to possible undesirable behaviors within
a subsystem.

For instance, the HS subsystem would be unable to find the authentication key
of the introduction point circuit leading to a BUG() warning and a duplicate
mark for close on the circuit.

This commit also adds a unit test to make sure we never select marked for
close circuits when upgrading its guard state from waiting for guard to open.

Fixes #30871

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

3 files changed, 57 insertions, 0 deletions

diff --git a/changes/ticket30871 b/changes/ticket30871
new file mode 100644
index 0000000000..81c076bb02
--- /dev/null
+++ b/changes/ticket30871
@@ -0,0 +1,6 @@
+  o Major bugfixes (circuit build, guard):
+    - When considering upgrading circuits from "waiting for guard" to "open",
+      always ignore the ones that are mark for close. Else, we can end up in
+      the situation where a subsystem is notified of that circuit opening but
+      still marked for close leading to undesirable behavior. Fixes bug 30871;
+      bugfix on 0.3.0.1-alpha.
diff --git a/src/feature/client/entrynodes.c b/src/feature/client/entrynodes.c
index 4afcee2021..54a9238d8f 100644
--- a/src/feature/client/entrynodes.c
+++ b/src/feature/client/entrynodes.c
@@ -2611,6 +2611,10 @@ entry_guards_upgrade_waiting_circuits(guard_selection_t *gs,
     entry_guard_t *guard = entry_guard_handle_get(state->guard);
     if (!guard || guard->in_selection != gs)
       continue;
+    if (TO_CIRCUIT(circ)->marked_for_close) {
+      /* Don't consider any marked for close circuits. */
+      continue;
+    }
 
     smartlist_add(all_circuits, circ);
   } SMARTLIST_FOREACH_END(circ);
diff --git a/src/test/test_circuitbuild.c b/src/test/test_circuitbuild.c
index 47218a559a..0c23091594 100644
--- a/src/test/test_circuitbuild.c
+++ b/src/test/test_circuitbuild.c
@@ -4,6 +4,8 @@
 /* See LICENSE for licensing information */
 
 #define CIRCUITBUILD_PRIVATE
+#define CIRCUITLIST_PRIVATE
+#define ENTRYNODES_PRIVATE
 
 #include "core/or/or.h"
 #include "test/test.h"
@@ -13,7 +15,11 @@
 #include "core/or/circuitbuild.h"
 #include "core/or/circuitlist.h"
 
+#include "core/or/cpath_build_state_st.h"
 #include "core/or/extend_info_st.h"
+#include "core/or/origin_circuit_st.h"
+
+#include "feature/client/entrynodes.h"
 
 /* Dummy nodes smartlist for testing */
 static smartlist_t dummy_nodes;
@@ -126,10 +132,51 @@ test_new_route_len_unhandled_exit(void *arg)
   UNMOCK(count_acceptable_nodes);
 }
 
+static void
+test_upgrade_from_guard_wait(void *arg)
+{
+  circuit_t *circ = NULL;
+  origin_circuit_t *orig_circ = NULL;
+  entry_guard_t *guard = NULL;
+  smartlist_t *list = NULL;
+
+  (void) arg;
+
+  circ = dummy_origin_circuit_new(0);
+  orig_circ = TO_ORIGIN_CIRCUIT(circ);
+  tt_assert(orig_circ);
+
+  orig_circ->build_state = tor_malloc_zero(sizeof(cpath_build_state_t));
+
+  circuit_set_state(circ, CIRCUIT_STATE_GUARD_WAIT);
+
+  /* Put it in guard wait state. */
+  guard = tor_malloc_zero(sizeof(*guard));
+  guard->in_selection = get_guard_selection_info();
+
+  orig_circ->guard_state =
+    circuit_guard_state_new(guard, GUARD_CIRC_STATE_WAITING_FOR_BETTER_GUARD,
+                            NULL);
+
+  /* Mark the circuit for close. */
+  circuit_mark_for_close(circ, END_CIRC_REASON_TORPROTOCOL);
+  tt_int_op(circ->marked_for_close, OP_NE, 0);
+
+  /* We shouldn't pick the mark for close circuit. */
+  list = circuit_find_circuits_to_upgrade_from_guard_wait();
+  tt_assert(!list);
+
+ done:
+  circuit_free(circ);
+  entry_guard_free_(guard);
+}
+
 struct testcase_t circuitbuild_tests[] = {
   { "noexit", test_new_route_len_noexit, 0, NULL, NULL },
   { "safe_exit", test_new_route_len_safe_exit, 0, NULL, NULL },
   { "unsafe_exit", test_new_route_len_unsafe_exit, 0, NULL, NULL },
   { "unhandled_exit", test_new_route_len_unhandled_exit, 0, NULL, NULL },
+  { "upgrade_from_guard_wait", test_upgrade_from_guard_wait, TT_FORK,
+    NULL, NULL },
   END_OF_TESTCASES
 };