hs: Handled REND_JOINED circuit when getting an INTRODUCE_ACK

Because we can get a RENDEZVOUS2 cell before the INTRODUCE_ACK, we need to
correctly handle the circuit purpose REND_JOINED that is not change its
purpose when we get an INTRODUCE_ACK and simply close the intro circuit
normally.

Fixes #23455

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

src/or/hs_circuitmap.c

@@ -407,9 +407,20 @@ hs_circuitmap_get_rend_circ_service_side(const uint8_t *cookie)
 }
 
 /* Public function: Return client-side rendezvous circuit with rendezvous
- * <b>cookie</b>. It will first lookup for the CIRCUIT_PURPOSE_C_REND_READY
- * purpose and then try for CIRCUIT_PURPOSE_C_REND_READY_INTRO_ACKED and then
- * finally tries for CIRCUIT_PURPOSE_C_ESTABLISH_REND.
+ * <b>cookie</b>. It will look for circuits with the following purposes:
+
+ * a) CIRCUIT_PURPOSE_C_REND_READY: Established rend circuit (received
+ *    RENDEZVOUS_ESTABLISHED). Waiting for RENDEZVOUS2 from service, and for
+ *    INTRODUCE_ACK from intro point.
+ *
+ * b) CIRCUIT_PURPOSE_C_REND_READY_INTRO_ACKED: Established rend circuit and
+ *    introduce circuit acked. Waiting for RENDEZVOUS2 from service.
+ *
+ * c) CIRCUIT_PURPOSE_C_REND_JOINED: Established rend circuit and received
+ *    RENDEZVOUS2 from service.
+ *
+ * d) CIRCUIT_PURPOSE_C_ESTABLISH_REND: Rend circuit open but not yet
+ *    established.
  *
  * Return NULL if no such circuit is found in the circuitmap. */
 origin_circuit_t *
@@ -431,6 +442,13 @@ hs_circuitmap_get_rend_circ_client_side(const uint8_t *cookie)
     return circ;
   }
 
+  circ = hs_circuitmap_get_origin_circuit(HS_TOKEN_REND_CLIENT_SIDE,
+                                          REND_TOKEN_LEN, cookie,
+                                          CIRCUIT_PURPOSE_C_REND_JOINED);
+  if (circ) {
+    return circ;
+  }
+
   circ = hs_circuitmap_get_origin_circuit(HS_TOKEN_REND_CLIENT_SIDE,
                                           REND_TOKEN_LEN, cookie,
                                           CIRCUIT_PURPOSE_C_ESTABLISH_REND);

src/or/hs_client.c

@@ -746,6 +746,14 @@ handle_introduce_ack_success(origin_circuit_t *intro_circ)
   }
 
   assert_circ_anonymity_ok(rend_circ, get_options());
+
+  /* It is possible to get a RENDEZVOUS2 cell before the INTRODUCE_ACK which
+   * means that the circuit will be joined and already transmitting data. In
+   * that case, simply skip the purpose change and close the intro circuit
+   * like it should be. */
+  if (TO_CIRCUIT(rend_circ)->purpose == CIRCUIT_PURPOSE_C_REND_JOINED) {
+    goto end;
+  }
   circuit_change_purpose(TO_CIRCUIT(rend_circ),
                          CIRCUIT_PURPOSE_C_REND_READY_INTRO_ACKED);
   /* Set timestamp_dirty, because circuit_expire_building expects it to