Leaving aside the correct advice to avoid such hard coded backup files, I wish people would recommend at least considering "sudo -e" instead of "sudo $EDITOR" when editing something important with root permissions.
sudo $EDITOR launches the editor itself as root, sudo -e launches the editor as a regular user on a temporary copy of the original file, and copies the contents back over to the original file when you are done. The less done as root, the less opportunity to mess things up.
Perhaps, but you will still overwrite it when you exit the editor and let sudo copy the contents back (that being said, there might be a race condition between closing the editor and sudo noticing that the process has terminated). Not sure if this would work, but a possible workaround could be to use /dev/shm (https://www.kernel.org/doc/gorman/html/understand/understand...).
The temporary file should be created in such a way that other users cannot modify it. If that does not happen, if other users can modify it, I would regard that as a bug.
Malicious processes running as the same user could potentially modify the file, but if you have malicious processes running as a user with sudo privileges you have probably already lost.
