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Full Discussion: Changing the user id or euid of the shell itself
Top Forums UNIX for Dummies Questions & Answers Changing the user id or euid of the shell itself Post 302528954 by Perderabo on Wednesday 8th of June 2011 09:37:44 AM
Old 06-08-2011
The guy that wrote the shell determines what system calls it invokes. It would be possible for the shell's author to give the shell's user access to any system call. Perl pretty much does this, but perl is not exactly a shell. But even if you wrote your own C program, you can't just change the euid of your own process... that would be terrible for security. The system calls that fiddle with the uid's only work as root. So the login process, which runs as root, can switch to your uid and then exec a shell. But you cannot switch back to root.

You can run an suid program like passwd to temporarily gain some limited root power. See: https://www.unix.com/tips-tutorials/1...rmissions.html for details on that.
 

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LEARN ABOUT NETBSD

chroot

CHROOT(8)						    BSD System Manager's Manual 						 CHROOT(8)

NAME

     chroot -- change root directory

SYNOPSIS

     chroot [-G group,group,...] [-g group] [-u user] newroot [command]

DESCRIPTION

     The chroot command changes its root directory to the supplied directory newroot and exec's command, or, if not supplied, an interactive copy
     of your shell.

     If the -u, -g, or -G options are given, the user, group, and group list of the process are set to these values after the chroot has taken
     place; see setgid(2), setgroups(2), setuid(2), getgrnam(3), and getpwnam(3).

     Note: command or the shell are run as your real-user-id.

ENVIRONMENT

     The following environment variable is referenced by chroot:

     SHELL  If set, the string specified by SHELL is interpreted as the name of the shell to exec.  If the variable SHELL is not set, /bin/sh is
	    used.

SEE ALSO

     ldd(1), chdir(2), chroot(2), environ(7)

HISTORY

     The chroot utility first appeared in 4.4BSD.

SECURITY CONSIDERATIONS

     chroot should never be installed setuid root, as it would then be possible to exploit the program to gain root privileges.

BSD
								  August 13, 2011							       BSD
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