Add proxy headers as early as possible.

This patch moves the logic that adds the proxy headers to an earlier
point in the exit connection lifetime, which ensures that the
application data cannot be written to the outbuf before the proxy header
is added.

See: https://bugs.torproject.org/4700

src/core/or/connection_edge.c

@@ -600,8 +600,7 @@ connected_cell_format_payload(uint8_t *payload_out,
 /* This is an onion service client connection: Export the client circuit ID
  * according to the HAProxy proxy protocol. */
 STATIC void
-export_hs_client_circuit_id(const edge_connection_t *edge_conn,
+export_hs_client_circuit_id(edge_connection_t *edge_conn,
-                            connection_t *conn,
                             hs_circuit_id_protocol_t protocol)
 {
   /* We only support HAProxy right now. */
@@ -633,7 +632,7 @@ export_hs_client_circuit_id(const edge_connection_t *edge_conn,
                gid >> 16, gid & 0x0000ffff,
                dst_ipv6, src_port, dst_port);
 
-  connection_buf_add(buf, strlen(buf), conn);
+  connection_buf_add(buf, strlen(buf), TO_CONN(edge_conn));
 
   tor_free(buf);
 }
@@ -659,14 +658,6 @@ connection_edge_finished_connecting(edge_connection_t *edge_conn)
 
   conn->state = EXIT_CONN_STATE_OPEN;
 
-  /* If it's an onion service connection, we might want to include the proxy
-   * protocol header: */
-  if (edge_conn->hs_ident) {
-    hs_circuit_id_protocol_t circuit_id_protocol =
-      hs_service_exports_circuit_id(&edge_conn->hs_ident->identity_pk);
-    export_hs_client_circuit_id(edge_conn, conn, circuit_id_protocol);
-  }
-
   connection_watch_events(conn, READ_EVENT); /* stop writing, keep reading */
   if (connection_get_outbuf_len(conn)) /* in case there are any queued relay
                                         * cells */
@@ -3452,6 +3443,14 @@ handle_hs_exit_conn(circuit_t *circ, edge_connection_t *conn)
 
   hs_inc_rdv_stream_counter(origin_circ);
 
+  /* If it's an onion service connection, we might want to include the proxy
+   * protocol header: */
+  if (conn->hs_ident) {
+    hs_circuit_id_protocol_t circuit_id_protocol =
+      hs_service_exports_circuit_id(&conn->hs_ident->identity_pk);
+    export_hs_client_circuit_id(conn, circuit_id_protocol);
+  }
+
   /* Connect tor to the hidden service destination. */
   connection_exit_connect(conn);
 

src/core/or/connection_edge.h

@@ -246,8 +246,7 @@ STATIC void connection_ap_handshake_rewrite(entry_connection_t *conn,
 
 STATIC int connection_ap_process_http_connect(entry_connection_t *conn);
 STATIC void
-export_hs_client_circuit_id(const edge_connection_t *edge_conn,
+export_hs_client_circuit_id(edge_connection_t *edge_conn,
-                            connection_t *conn,
                             hs_circuit_id_protocol_t protocol);
 
 #endif /* defined(CONNECTION_EDGE_PRIVATE) */

src/test/test_hs_service.c

@@ -2047,8 +2047,7 @@ test_export_client_circuit_id(void *arg)
   or_circ->global_identifier = 666;
 
   /* Export circuit ID */
-  export_hs_client_circuit_id(edge_conn, conn,
+  export_hs_client_circuit_id(edge_conn, service->config.circuit_id_protocol);
-                              service->config.circuit_id_protocol);
 
   /* Check contents */
   cp1 = buf_get_contents(conn->outbuf, &sz);
@@ -2059,8 +2058,7 @@ test_export_client_circuit_id(void *arg)
   or_circ->global_identifier = 22;
 
   /* check changes */
-  export_hs_client_circuit_id(edge_conn, conn,
+  export_hs_client_circuit_id(edge_conn, service->config.circuit_id_protocol);
-                              service->config.circuit_id_protocol);
   cp2 = buf_get_contents(conn->outbuf, &sz);
   tt_str_op(cp1, OP_NE, cp2);
   tor_free(cp1);
@@ -2068,8 +2066,7 @@ test_export_client_circuit_id(void *arg)
   /* Check that GID with UINT32_MAX works. */
   or_circ->global_identifier = UINT32_MAX;
 
-  export_hs_client_circuit_id(edge_conn, conn,
+  export_hs_client_circuit_id(edge_conn, service->config.circuit_id_protocol);
-                              service->config.circuit_id_protocol);
   cp1 = buf_get_contents(conn->outbuf, &sz);
   tt_str_op(cp1, OP_EQ,
             "PROXY TCP6 fc00:dead:beef:4dad::ffff:ffff ::1 65535 42\r\n");
@@ -2078,8 +2075,7 @@ test_export_client_circuit_id(void *arg)
   /* Check that GID with UINT16_MAX works. */
   or_circ->global_identifier = UINT16_MAX;
 
-  export_hs_client_circuit_id(edge_conn, conn,
+  export_hs_client_circuit_id(edge_conn, service->config.circuit_id_protocol);
-                              service->config.circuit_id_protocol);
   cp1 = buf_get_contents(conn->outbuf, &sz);
   tt_str_op(cp1, OP_EQ,
             "PROXY TCP6 fc00:dead:beef:4dad::0:ffff ::1 65535 42\r\n");
@@ -2088,8 +2084,7 @@ test_export_client_circuit_id(void *arg)
   /* Check that GID with UINT16_MAX + 7 works. */
   or_circ->global_identifier = UINT16_MAX + 7;
 
-  export_hs_client_circuit_id(edge_conn, conn,
+  export_hs_client_circuit_id(edge_conn, service->config.circuit_id_protocol);
-                              service->config.circuit_id_protocol);
   cp1 = buf_get_contents(conn->outbuf, &sz);
   tt_str_op(cp1, OP_EQ, "PROXY TCP6 fc00:dead:beef:4dad::1:6 ::1 6 42\r\n");