Use an alternate mechanism for CreateFile calls in Chrome

chrome_elf/create_file/chrome_create_file.cc

+// Copyright 2013 The Chromium Authors. All rights reserved.
+// Use of this source code is governed by a BSD-style license that can be
+// found in the LICENSE file.
+
+#include "chrome_elf/create_file/chrome_create_file.h"
+
+#include <string>
+
+#include "base/strings/string16.h"
+#include "chrome_elf/chrome_elf_constants.h"
+#include "chrome_elf/ntdll_cache.h"
+#include "sandbox/win/src/nt_internals.h"
+
+namespace {
+
+// From ShlObj.h in the Windows SDK.
+#define CSIDL_LOCAL_APPDATA 0x001c
+
+typedef BOOL (WINAPI *PathIsUNCFunction)(
+  IN LPCWSTR path);
+
+typedef BOOL (WINAPI *PathAppendFunction)(
+  IN LPWSTR path,
+  IN LPCWSTR more);
+
+typedef BOOL (WINAPI *PathIsPrefixFunction)(
+  IN LPCWSTR prefix,
+  IN LPCWSTR path);
+
+typedef HRESULT (WINAPI *SHGetFolderPathFunction)(
+  IN HWND hwnd_owner,
+  IN int folder,
+  IN HANDLE token,
+  IN DWORD flags,
+  OUT LPWSTR path);
+
+PathIsUNCFunction g_path_is_unc_func;
+PathAppendFunction g_path_append_func;
+PathIsPrefixFunction g_path_is_prefix_func;
+SHGetFolderPathFunction g_get_folder_func;
+
+// Populates the g_*_func pointers to functions which will be used in
+// ShouldBypass(). Chrome_elf cannot have a load-time dependency on shell32 or
+// shlwapi as this would induce a load-time dependency on user32.dll. Instead,
+// the addresses of the functions we need are retrieved the first time this
+// method is called, and cached to avoid subsequent calls to GetProcAddress().
+// It is assumed that the host process will never unload these functions.
+// Returns true if all the functions needed are present.
+bool PopulateShellFunctions() {
+  // Early exit if functions have already been populated.
+  if (g_path_is_unc_func && g_path_append_func &&
+      g_path_is_prefix_func && g_get_folder_func) {
+    return true;
+  }
+
+  // Get the addresses of the functions we need and store them for future use.
+  // These handles are intentionally leaked to ensure that these modules do not
+  // get unloaded.
+  HMODULE shell32 = ::LoadLibrary(L"shell32.dll");
+  HMODULE shlwapi = ::LoadLibrary(L"shlwapi.dll");
+
+  if (!shlwapi || !shell32)
+    return false;
+
+  g_path_is_unc_func = reinterpret_cast<PathIsUNCFunction>(
+      ::GetProcAddress(shlwapi, "PathIsUNCW"));
+  g_path_append_func = reinterpret_cast<PathAppendFunction>(
+      ::GetProcAddress(shlwapi, "PathAppendW"));
+  g_path_is_prefix_func = reinterpret_cast<PathIsPrefixFunction>(
+      ::GetProcAddress(shlwapi, "PathIsPrefixW"));
+  g_get_folder_func = reinterpret_cast<SHGetFolderPathFunction>(
+      ::GetProcAddress(shell32, "SHGetFolderPathW"));
+
+  return g_path_is_unc_func && g_path_append_func &&
+      g_path_is_prefix_func && g_get_folder_func;
+}
+
+}  // namespace
+
+HANDLE WINAPI CreateFileWRedirect(
+    LPCWSTR file_name,
+    DWORD desired_access,
+    DWORD share_mode,
+    LPSECURITY_ATTRIBUTES security_attributes,
+    DWORD creation_disposition,
+    DWORD flags_and_attributes,
+    HANDLE template_file) {
+  if (ShouldBypass(file_name)) {
+    return CreateFileNTDLL(file_name,
+                           desired_access,
+                           share_mode,
+                           security_attributes,
+                           creation_disposition,
+                           flags_and_attributes,
+                           template_file);
+  }
+  return CreateFile(file_name,
+                    desired_access,
+                    share_mode,
+                    security_attributes,
+                    creation_disposition,
+                    flags_and_attributes,
+                    template_file);
+
+}
+
+HANDLE CreateFileNTDLL(
+    LPCWSTR file_name,
+    DWORD desired_access,
+    DWORD share_mode,
+    LPSECURITY_ATTRIBUTES security_attributes,
+    DWORD creation_disposition,
+    DWORD flags_and_attributes,
+    HANDLE template_file) {
+  HANDLE file_handle = INVALID_HANDLE_VALUE;
+  NTSTATUS result = STATUS_UNSUCCESSFUL;
+  IO_STATUS_BLOCK io_status_block = {};
+
+  // Convert from Win32 domain to to NT creation disposition values.
+  switch (creation_disposition) {
+    case CREATE_NEW:
+      creation_disposition = FILE_CREATE;
+      break;
+    case CREATE_ALWAYS:
+      creation_disposition = FILE_OVERWRITE_IF;
+      break;
+    case OPEN_EXISTING:
+      creation_disposition = FILE_OPEN;
+      break;
+    case OPEN_ALWAYS:
+      creation_disposition = FILE_OPEN_IF;
+      break;
+    case TRUNCATE_EXISTING:
+      creation_disposition = FILE_OVERWRITE;
+      break;
+    default:
+      SetLastError(ERROR_INVALID_PARAMETER);
+      return INVALID_HANDLE_VALUE;
+  }
+
+  if (!g_ntdll_lookup["NtCreateFile"] ||
+      !g_ntdll_lookup["RtlInitUnicodeString"]) {
+    return INVALID_HANDLE_VALUE;
+  }
+
+  NtCreateFileFunction create_file =
+      reinterpret_cast<NtCreateFileFunction>(g_ntdll_lookup["NtCreateFile"]);
+
+  RtlInitUnicodeStringFunction init_unicode_string =
+      reinterpret_cast<RtlInitUnicodeStringFunction>(
+          g_ntdll_lookup["RtlInitUnicodeString"]);
+
+  UNICODE_STRING path_unicode_string;
+
+  // Format the path into an NT path. Arguably this should be done with
+  // RtlDosPathNameToNtPathName_U, but afaict this is equivalent for
+  // local paths. Using this with a UNC path name will almost certainly
+  // break in interesting ways.
+  base::string16 filename_string(L"\\??\\");
+  filename_string += file_name;
+
+  init_unicode_string(&path_unicode_string, filename_string.c_str());
+
+  OBJECT_ATTRIBUTES path_attributes = {};
+  InitializeObjectAttributes(&path_attributes,
+                             &path_unicode_string,
+                             OBJ_CASE_INSENSITIVE,
+                             NULL,   // No Root Directory
+                             NULL);  // No Security Descriptor
+
+  // Set create_options, desired_access, and flags_and_attributes to match those
+  // set by kernel32!CreateFile.
+  ULONG create_options = FILE_ATTRIBUTE_DEVICE | FILE_ATTRIBUTE_ARCHIVE;
+  desired_access |= 0x100080;
+  flags_and_attributes &= 0x2FFA7;
+
+  result = create_file(&file_handle,
+                       desired_access,
+                       &path_attributes,
+                       &io_status_block,
+                       0,  // Allocation size
+                       flags_and_attributes,
+                       share_mode,
+                       creation_disposition,
+                       create_options,
+                       NULL,
+                       0);
+
+  if (result != STATUS_SUCCESS) {
+    if (result == STATUS_OBJECT_NAME_COLLISION &&
+        creation_disposition == FILE_CREATE) {
+      SetLastError(ERROR_FILE_EXISTS);
+    }
+    return INVALID_HANDLE_VALUE;
+  }
+
+  if (creation_disposition == FILE_OPEN_IF) {
+    SetLastError(io_status_block.Information == FILE_OPENED ?
+        ERROR_ALREADY_EXISTS : ERROR_SUCCESS);
+  } else if (creation_disposition == FILE_OVERWRITE_IF) {
+    SetLastError(io_status_block.Information == FILE_OVERWRITTEN ?
+        ERROR_ALREADY_EXISTS : ERROR_SUCCESS);
+  } else {
+    SetLastError(ERROR_SUCCESS);
+  }
+
+  return file_handle;
+}
+
+bool ShouldBypass(LPCWSTR file_name) {
+  // If the shell functions are not present, forward the call to kernel32.
+  if (!PopulateShellFunctions())
+    return false;
+
+  // Forward all UNC filepaths to kernel32.
+  if (g_path_is_unc_func(file_name))
+    return false;
+
+  wchar_t local_appdata_path[MAX_PATH];
+
+  // Get the %LOCALAPPDATA% Path and append the location of our UserData
+  // directory to it.
+  HRESULT appdata_result = g_get_folder_func(
+      NULL, CSIDL_LOCAL_APPDATA, NULL, 0, local_appdata_path);
+
+  // If getting the %LOCALAPPDATA% path or appending to it failed, then forward
+  // the call to kernel32.
+  if (!SUCCEEDED(appdata_result) ||
+      !g_path_append_func(local_appdata_path, kAppDataDirName) ||
+      !g_path_append_func(local_appdata_path, kUserDataDirName)) {
+    return false;
+  }
+
+  // Check if we are trying to access something in the UserData dir. If so,
+  // then redirect the call to bypass kernel32.
+  return !!g_path_is_prefix_func(local_appdata_path, file_name);
+}