add restricted filesystem access to sel_ldr

src/trusted/service_runtime/nacl_syscall_common.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 service run-time, non-platform specific system call helper routines.
  */
 #include <sys/types.h>
 #include <sys/stat.h>
 
 #include <errno.h>
 #include <stdio.h>
+#include <string.h>
 
 #include "native_client/src/include/build_config.h"
 
 #if NACL_WINDOWS
 #include <windows.h>
 #endif
 
 #include "native_client/src/trusted/service_runtime/nacl_syscall_common.h"
 
 #include "native_client/src/include/nacl_macros.h"
@@ skipping 59 matching lines @@
   return 0;
 }
 
 int NaClAclBypassChecks = 0;
 
 void NaClInsecurelyBypassAllAclChecks(void) {
   NaClLog(LOG_WARNING, "BYPASSING ALL ACL CHECKS\n");
   NaClAclBypassChecks = 1;
 }
 
+char *NaClRootFolder = NULL;
+size_t NaClRootFolderLen = 0;
+
+void NaClMountRootFolder(char *root) {
+  /*
+   * TODO(jtolds): sanitize root, make sure it's well-formed, and does not
+   * end with a trailing slash.

[jtolds, 2015/06/25 23:05:05]

hmm, i guess we'll need to use a path separator. not sure how this prefix
approach works with windows and drive letters. do binaries inside native client
use backslashes and drive letters?

[Mark Seaborn, 2015/06/25 23:55:08]

I also don't know what the exact rules would need to be for Windows.

It would be reasonable to make this functionality Unix-only for this CL.  So
"-m" could report an error on Windows.

+   */
+  NaClRootFolder = strdup(root);
+  NaClRootFolderLen = strlen(NaClRootFolder);
+}
+
+int NaClFileAccessEnabled(void) {
+  return NaClAclBypassChecks || (NaClRootFolder != NULL);
+}
+
 int NaClHighResolutionTimerEnabled(void) {
   return NaClAclBypassChecks;
 }
 
 int32_t NaClSysGetpid(struct NaClAppThread *natp) {
   int32_t pid;
   UNREFERENCED_PARAMETER(natp);
 
   if (NaClAclBypassChecks) {
     pid = GETPID();
@@ skipping 594 matching lines @@
 #else
 #error Unsupported platform
 #endif
       break;
     }
     case NACL_ABI__SC_PAGESIZE: {
       result_value = 1 << 16;  /* always 64k pages */
       break;
     }
     case NACL_ABI__SC_NACL_FILE_ACCESS_ENABLED: {
-      result_value = NaClAclBypassChecks;
+      result_value = NaClFileAccessEnabled();
       break;
     }
     case NACL_ABI__SC_NACL_LIST_MAPPINGS_ENABLED: {
       result_value = nap->enable_list_mappings;
       break;
     }
     case NACL_ABI__SC_NACL_PNACL_MODE: {
       result_value = nap->pnacl_mode;
       break;
     }
@@ skipping 288 matching lines @@
   return NaClSysClockGetCommon(natp, clk_id, (uintptr_t) tsp,
                                NaClClockGetRes, 1);
 }
 
 int32_t NaClSysClockGetTime(struct NaClAppThread  *natp,
                             int                   clk_id,
                             uint32_t              tsp) {
   return NaClSysClockGetCommon(natp, clk_id, (uintptr_t) tsp,
                                NaClClockGetTime, 0);
 }