Here, we're going to help you do just that. We'll review how setuid, setgid, and the sticky bit work and provide a list of common commands to help you get started. Before diving into the world of umask, setuid, and setgid, we recommend reading up on file permissions, chmod, and chown.
If you're already comfortable with chmod and chown, let's dive right in! Setuid and setgid are a way for users to run an executable with the permissions of the user setuid or group setgid who owns the file. To understand why setuid and setgid are needed, let's start with how things work without them.
If neither your user, nor any of your real or effective groups have access, neither will you. Let's walk through a simple example using the ls command.
Both subdirectories are owned by root. The secret1 subdirectory allows read and execute permissions to everyone else. The secret2 subdirectory grants no privileges to everyone else.
That's because when running with our "cooluser" account's privileges, the system denies ls access to the secret2 subdirectory. If we switch to the root or use sudo account, ls works fine on the secret2 subdirectory. This makes sense because now ls has the privileges associated with the root user.
A user's privileges should dictate what the commands they execute can and cannot do. However, in some cases, you may need a user to run a program with more privileges — usually root privileges — than they have by default.
The textbook case for this is the passwd command that allows users to change their own password. Under normal circumstances, that suggests we'd need to be root or have sudo privileges to change our password.
However, normal users can execute the passwd command to change their own password without sudo or root permissions. To understand why passwd seemingly grants root-level access but ls doesn't, let's take a look at the permissions on those two executables.
Both executables are owned by the root user and group, and there is only one difference in the permissions. As you can see, the passwd executable has an "s" where you'd expect an "x" for the file owner's permissions. This "s" tells us the setuid bit is set.
However they are also risky, a small mistake in a setuid program can easily expose more than was meant to be exposed. Various debugging related features are also disabled for setuid programs to prevent them being used to bypass the restrictions. In recent times Linux systems have been replacing some uses of "setuid" with a new mechanism called "capabilities" which allows for finer-grained allocation of special privileges to programs. Sign up to join this community. The best answers are voted up and rise to the top.
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Edward Davis Posted May 24, 0 Comments. I prefer sudo over RBAC. Good luck.
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