safer os.chmod for wallet files and config: set perms before write

Set unix file permissions first, before writing data.

electrum/gui/qt/main_window.py

@@ -2332,7 +2332,7 @@ def on_dialog_closed(*args):
 
  def do_export_privkeys(self, fileName, pklist, is_csv):
  with open(fileName, "w+") as f:
- os_chmod(fileName, 0o600)
+ os_chmod(fileName, 0o600) # set restrictive perms *before* we write data
  if is_csv:
  transaction = csv.writer(f)
  transaction.writerow(["address", "private_key"])

electrum/simple_config.py

@@ -421,8 +421,8 @@ def save_user_config(self):
  s = json.dumps(self.user_config, indent=4, sort_keys=True)
  try:
  with open(path, "w", encoding='utf-8') as f:
+ os_chmod(path, stat.S_IREAD | stat.S_IWRITE) # set restrictive perms *before* we write data
  f.write(s)
- os_chmod(path, stat.S_IREAD | stat.S_IWRITE)
  except OSError:
  # datadir probably deleted while running... e.g. portable exe running on ejected USB drive
  # (in which case it is typically either FileNotFoundError or PermissionError,

electrum/storage.py

@@ -87,22 +87,22 @@ def read(self):
  return self.decrypted if self.is_encrypted() else self.raw
 
  def write(self, data: str) -> None:
+ try:
+ mode = os.stat(self.path).st_mode
+ except FileNotFoundError:
+ mode = stat.S_IREAD | stat.S_IWRITE
  s = self.encrypt_before_writing(data)
  temp_path = "%s.tmp.%s" % (self.path, os.getpid())
  with open(temp_path, "wb") as f:
+ os_chmod(temp_path, mode) # set restrictive perms *before* we write data
  f.write(s.encode("utf-8"))
  self.pos = f.seek(0, os.SEEK_END)
  f.flush()
  os.fsync(f.fileno())
- try:
- mode = os.stat(self.path).st_mode
- except FileNotFoundError:
- mode = stat.S_IREAD | stat.S_IWRITE
  # assert that wallet file does not exist, to prevent wallet corruption (see issue #5082)
  if not self.file_exists():
  assert not os.path.exists(self.path)
  os.replace(temp_path, self.path)
- os_chmod(self.path, mode)
  self._file_exists = True
  self.logger.info(f"saved {self.path}")