February 2003
Intermediate to advanced
986 pages
35h 34m
English
book
Practical UNIX and Internet Security, 3rd Edition
by Simson Garfinkel, Gene Spafford, Alan Schwartz
Content preview from Practical UNIX and Internet Security, 3rd Edition
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SUID and SGID
Sometimes, unprivileged users must be able to accomplish tasks that require privileges. An example is the passwd program, which allows you to change your password. Changing a user’s password requires modifying the password field in the /etc/passwd file. However, you should not give a user access to change this file directly—the user could change everybody else’s password as well! Likewise, the mail program requires that you insert a message into the mailbox of another user, yet you should not give one user unrestricted access to another’s mailbox.
To get around these problems, Unix allows programs to be endowed with privileges. Processes executing these programs can assume another UID or GID when they’re running. A program that changes its UID is called a SUID program (set-UID); a program that changes its GID is called a SGID program (set-GID). A program can be both SUID and SGID at the same time.
When a SUID program is run, its effective UID (see Chapter 4) becomes that of the owner of the file, rather than of the user who is running it.
Sticky Bits
If a
program is SUID or SGID, the output of the
ls -l command will have the x
in the display changed to an s. If the program is
sticky, the last x changes to a
t as shown in Figure 6-3 and
Table 6-14.
Figure 6-3. Additional file permissions
Table 6-14. SUID, SGID, and sticky bits
|
Contents |
Permission |
Meaning |
|---|---|---|
|
---s------ ... |
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O’Reilly covers everything we've got, with content to help us build a world-class technology community, upgrade the capabilities and competencies of our teams, and improve overall team performance as well as their engagement.Julian F.
I wanted to learn C and C++, but it didn't click for me until I picked up an O'Reilly book. When I went on the O’Reilly platform, I was astonished to find all the books there, plus live events and sandboxes so you could play around with the technology.Addison B.
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I'm always learning. So when I got on to O'Reilly, I was like a kid in a candy store. There are playlists. There are answers. There's on-demand training. It's worth its weight in gold, in terms of what it allows me to do.