Fix a crash bug in cell queues: It is possible for a connection_write_to_buf...

Fix a crash bug in cell queues: It is possible for a connection_write_to_buf to close the connection or otherwise unlink the circuit, which makes the circuit nonactive, which invalidates the pointer from the circuit to the next circuit on the active ring.  Also add a bunch of asserts, most #ifdefed out.

svn:r9915

src/or/circuitlist.c

@@ -103,7 +103,7 @@ circuit_set_circid_orconn_helper(circuit_t *circ, uint16_t id,
       tor_free(found);
       --old_conn->n_circuits;
     }
-    if (active)
+    if (active && old_conn != conn)
       make_circuit_inactive_on_conn(circ,old_conn);
   }
 
@@ -123,7 +123,7 @@ circuit_set_circid_orconn_helper(circuit_t *circ, uint16_t id,
     found->circuit = circ;
     HT_INSERT(orconn_circid_map, &orconn_circid_circuit_map, found);
   }
-  if (active)
+  if (active && old_conn != conn)
     make_circuit_active_on_conn(circ,conn);
 
   ++conn->n_circuits;
@@ -145,6 +145,7 @@ circuit_set_p_circid_orconn(or_circuit_t *circ, uint16_t id,
   circ->p_circ_id = id;
   circ->p_conn = conn;
   active = circ->p_conn_cells.n > 0;
+  tor_assert(bool_eq(active, circ->next_active_on_p_conn));
 
   if (id == old_id && conn == old_conn)
     return;
@@ -168,6 +169,7 @@ circuit_set_n_circid_orconn(circuit_t *circ, uint16_t id,
   circ->n_circ_id = id;
   circ->n_conn = conn;
   active = circ->n_conn_cells.n > 0;
+  tor_assert(bool_eq(active, circ->next_active_on_n_conn));
 
   if (id == old_id && conn == old_conn)
     return;

src/or/relay.c

@@ -1470,6 +1470,13 @@ circuit_consider_sending_sendme(circuit_t *circ, crypt_path_t *layer_hint)
  * cells. */
 #define CELL_QUEUE_LOWWATER_SIZE 64
 
+#ifdef ACTIVE_CIRCUITS_PARANOIA
+#define assert_active_circuits_ok_paranoid(conn) \
+     assert_active_circuits_ok(conn)
+#else
+#define assert_active_circuits_ok_paranoid(conn)
+#endif
+
 /** Release storage held by <b>cell</b> */
 static INLINE void
 cell_free(cell_t *cell)
@@ -1546,6 +1553,8 @@ cell_queue_pop(cell_queue_t *queue)
 static INLINE circuit_t **
 next_circ_on_conn_p(circuit_t *circ, or_connection_t *conn)
 {
+  tor_assert(circ);
+  tor_assert(conn);
   if (conn == circ->n_conn) {
     return &circ->next_active_on_n_conn;
   } else {
@@ -1560,6 +1569,8 @@ next_circ_on_conn_p(circuit_t *circ, or_connection_t *conn)
 static INLINE circuit_t **
 prev_circ_on_conn_p(circuit_t *circ, or_connection_t *conn)
 {
+  tor_assert(circ);
+  tor_assert(conn);
   if (conn == circ->n_conn) {
     return &circ->prev_active_on_n_conn;
   } else {
@@ -1589,6 +1600,7 @@ make_circuit_active_on_conn(circuit_t *circ, or_connection_t *conn)
     *prev_circ_on_conn_p(head, conn) = circ;
     *prev_circ_on_conn_p(circ, conn) = old_tail;
   }
+  assert_active_circuits_ok_paranoid(conn);
 }
 
 /** Remove <b>circ</b> to the list of circuits with pending cells on
@@ -1598,6 +1610,7 @@ make_circuit_inactive_on_conn(circuit_t *circ, or_connection_t *conn)
 {
   circuit_t *next = *next_circ_on_conn_p(circ, conn);
   circuit_t *prev = *prev_circ_on_conn_p(circ, conn);
+  tor_assert(next && prev);
   tor_assert(*prev_circ_on_conn_p(next, conn) == circ);
   tor_assert(*next_circ_on_conn_p(prev, conn) == circ);
 
@@ -1611,6 +1624,7 @@ make_circuit_inactive_on_conn(circuit_t *circ, or_connection_t *conn)
   }
   *prev_circ_on_conn_p(circ, conn) = NULL;
   *next_circ_on_conn_p(circ, conn) = NULL;
+  assert_active_circuits_ok_paranoid(conn);
 }
 
 /** Remove all circuits from the list of circuits with pending cells on
@@ -1677,6 +1691,7 @@ connection_or_flush_from_first_active_circuit(or_connection_t *conn, int max)
   int streams_blocked;
   circ = conn->active_circuits;
   if (!circ) return 0;
+  assert_active_circuits_ok_paranoid(conn);
   if (circ->n_conn == conn) {
     queue = &circ->n_conn_cells;
     streams_blocked = circ->streams_blocked_on_n_conn;
@@ -1684,14 +1699,27 @@ connection_or_flush_from_first_active_circuit(or_connection_t *conn, int max)
     queue = &TO_OR_CIRCUIT(circ)->p_conn_cells;
     streams_blocked = circ->streams_blocked_on_p_conn;
   }
+  tor_assert(*next_circ_on_conn_p(circ,conn));
 
   for (n_flushed = 0; n_flushed < max && queue->head; ++n_flushed) {
     cell_t *cell = cell_queue_pop(queue);
+    tor_assert(*next_circ_on_conn_p(circ,conn));
 
     connection_or_write_cell_to_buf(cell, conn);
     cell_free(cell);
     ++n_flushed;
+    if (circ != conn->active_circuits) {
+      /* If this happens, the current circuit just got made inactive by
+       * a call in connection_write_to_buf().  That's nothing to worry about:
+       * circuit_make_inactive_on_conn() already advanced conn->active_circuits
+       * for us.
+       */
+      assert_active_circuits_ok_paranoid(conn);
+      return n_flushed;
+    }
   }
+  tor_assert(*next_circ_on_conn_p(circ,conn));
+  assert_active_circuits_ok_paranoid(conn);
   conn->active_circuits = *next_circ_on_conn_p(circ, conn);
 
   /* Is the cell queue low enough to unblock all the streams that are waiting