hs-v3: Close client intro circuits if the descriptor is replaced

When storing a descriptor in the client cache, if we are about to replace an
existing descriptor, make sure to close every introduction circuits of the old
descriptor so we don't have leftovers lying around.

Ticket 27471 describes a situation where tor is sending an INTRODUCE1 cell on
an introduction circuit for which it doesn't have a matching intro point
object (taken from the descriptor).

The main theory is that, after a new descriptor showed up, the introduction
points changed which led to selecting an introduction circuit not used by the
service anymore thus for which we are unable to find the corresponding
introduction point within the descriptor we just fetched.

Closes #27471.

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

src/core/or/circuitlist.c

@@ -1644,15 +1644,24 @@ circuit_get_ready_rend_circ_by_rend_data(const rend_data_t *rend_data)
   return NULL;
 }
 
-/** Return the first service introduction circuit originating from the global
- * circuit list after <b>start</b> or at the start of the list if <b>start</b>
- * is NULL. Return NULL if no circuit is found.
+/** Return the first introduction circuit originating from the global circuit
+ * list after <b>start</b> or at the start of the list if <b>start</b> is
+ * NULL. Return NULL if no circuit is found.
  *
- * A service introduction point circuit has a purpose of either
- * CIRCUIT_PURPOSE_S_ESTABLISH_INTRO or CIRCUIT_PURPOSE_S_INTRO. This does not
- * return a circuit marked for close and its state must be open. */
+ * If <b>want_client_circ</b> is true, then we are looking for client-side
+ * introduction circuits: A client introduction point circuit has a purpose of
+ * either CIRCUIT_PURPOSE_C_INTRODUCING, CIRCUIT_PURPOSE_C_INTRODUCE_ACK_WAIT
+ * or CIRCUIT_PURPOSE_C_INTRODUCE_ACKED. This does not return a circuit marked
+ * for close, but it returns circuits regardless of their circuit state.
+ *
+ * If <b>want_client_circ</b> is false, then we are looking for service-side
+ * introduction circuits: A service introduction point circuit has a purpose of
+ * either CIRCUIT_PURPOSE_S_ESTABLISH_INTRO or CIRCUIT_PURPOSE_S_INTRO. This
+ * does not return circuits marked for close, or in any state other than open.
+ */
 origin_circuit_t *
-circuit_get_next_service_intro_circ(origin_circuit_t *start)
+circuit_get_next_intro_circ(const origin_circuit_t *start,
+                            bool want_client_circ)
 {
   int idx = 0;
   smartlist_t *lst = circuit_get_global_list();
@@ -1664,13 +1673,29 @@ circuit_get_next_service_intro_circ(origin_circuit_t *start)
   for ( ; idx < smartlist_len(lst); ++idx) {
     circuit_t *circ = smartlist_get(lst, idx);
 
-    /* Ignore a marked for close circuit or purpose not matching a service
-     * intro point or if the state is not open. */
-    if (circ->marked_for_close || circ->state != CIRCUIT_STATE_OPEN ||
-        (circ->purpose != CIRCUIT_PURPOSE_S_ESTABLISH_INTRO &&
-         circ->purpose != CIRCUIT_PURPOSE_S_INTRO)) {
+    /* Ignore a marked for close circuit or if the state is not open. */
+    if (circ->marked_for_close) {
       continue;
     }
+
+    /* Depending on whether we are looking for client or service circs, skip
+     * circuits with other purposes. */
+    if (want_client_circ) {
+      if (circ->purpose != CIRCUIT_PURPOSE_C_INTRODUCING &&
+          circ->purpose != CIRCUIT_PURPOSE_C_INTRODUCE_ACK_WAIT &&
+          circ->purpose != CIRCUIT_PURPOSE_C_INTRODUCE_ACKED) {
+        continue;
+      }
+    } else { /* we are looking for service-side circs */
+      if (circ->state != CIRCUIT_STATE_OPEN) {
+        continue;
+      }
+      if (circ->purpose != CIRCUIT_PURPOSE_S_ESTABLISH_INTRO &&
+          circ->purpose != CIRCUIT_PURPOSE_S_INTRO) {
+        continue;
+      }
+    }
+
     /* The purposes we are looking for are only for origin circuits so the
      * following is valid. */
     return TO_ORIGIN_CIRCUIT(circ);

src/core/or/circuitlist.h

@@ -202,7 +202,8 @@ origin_circuit_t *circuit_get_ready_rend_circ_by_rend_data(
   const rend_data_t *rend_data);
 origin_circuit_t *circuit_get_next_by_pk_and_purpose(origin_circuit_t *start,
                                      const uint8_t *digest, uint8_t purpose);
-origin_circuit_t *circuit_get_next_service_intro_circ(origin_circuit_t *start);
+origin_circuit_t *circuit_get_next_intro_circ(const origin_circuit_t *start,
+                                              bool want_client_circ);
 origin_circuit_t *circuit_get_next_service_rp_circ(origin_circuit_t *start);
 origin_circuit_t *circuit_get_next_service_hsdir_circ(origin_circuit_t *start);
 origin_circuit_t *circuit_find_to_cannibalize(uint8_t purpose,