Tham khảo tài liệu 'advanced linux programming: 10-security', công nghệ thông tin, hệ điều hành phục vụ nhu cầu học tập, nghiên cứu và làm việc hiệu quả | Security UCH OF THE POWER OF A GNU LINUX SYSTEM COMES FROM its support for multiple users and for networking. Many people can use the system at once and they can connect to the system from remote locations. Unfortunately with this power comes risk especially for systems connected to the Internet. Under some circumstances a remote hacker can connect to the system and read modify or remove files that are stored on the machine. Or two users on the same machine can read modify or remove each other s files when they should not be allowed to do this happens the system s security is said to have been compromised. The Linux kernel provides a variety of facilities to ensure that these events do not take place. But to avoid security breaches ordinary applications must be careful as well. For example imagine that you are developing accounting software. Although you might want all users to be able to file expense reports with the system you wouldn t want all users to be able to approve those might want users to be able to view their own payroll information but you certainly wouldn t want them to be able to view everyone else s payroll might want managers to be able to view the salaries of employees in their departments but you wouldn t want them to view the salaries of employees in other departments. 198 Chapter 10 Security To enforce these kinds of controls you have to be very careful. It s amazingly easy to make a mistake that allows users to do something you didn t intend them to be able to best approach is to enlist the help of security experts. Still every application developer ought to understand the basics. Users and Groups Each Linux user is assigned a unique number called a user ID or UID. Of course when you log in you use a username rather than a user ID. The system converts your username to a particular user ID and from then on it s only the user ID that counts. You can actually have more than one username for the same
