Extended restricted filesystem to support relative paths.

src/trusted/service_runtime/sel_main.c

 /*
  * Copyright (c) 2012 The Native Client Authors. All rights reserved.
  * Use of this source code is governed by a BSD-style license that can be
  * found in the LICENSE file.
  */
 
 /*
  * NaCl Simple/secure ELF loader (NaCl SEL).
  */
 #include "native_client/src/include/build_config.h"
@@ skipping 726 matching lines @@
 
   /*
    * Make sure all the file buffers are flushed before entering
    * the application code.
    */
   fflush((FILE *) NULL);
 
   NaClAppStartModule(nap, NULL, NULL);
 
   /*
-   * For restricted file access, change directory to the root
-   * of the restricted directory.
+   * For restricted file access, change directory to the root of the restricted
+   * directory. This is required for safety, because we allow relative
+   * pathnames.
    */
   if (NaClRootDir != NULL && NaClHostDescChdir(NaClRootDir)) {
     NaClLog(LOG_FATAL, "Could not change directory to root dir\n");
   }
 
   /*
    * error reporting done; can quit now if there was an error earlier.
    */
   if (LOAD_OK != errcode) {
     NaClLog(4,
@@ skipping 57 matching lines @@
 #if NACL_LINUX
   NaClSignalHandlerFini();
 #endif
   NaClAllModulesFini();
 
   NaClExit(ret_code);
 
   /* Unreachable, but having the return prevents a compiler error. */
   return ret_code;
 }