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doc: Add "Setuid Programs" node.

* doc/guix.texi (Setuid Programs): New node.
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Ludovic Courtès 2014-07-17 18:10:16 +02:00
parent fd1b1fa296
commit 0ae8c15aef
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@ -2847,6 +2847,7 @@ instance to support new system services.
* File Systems:: Configuring file system mounts.
* User Accounts:: Specifying user accounts.
* Services:: Specifying system services.
* Setuid Programs:: Programs running with root privileges.
* Initial RAM Disk:: Linux-Libre bootstrapping.
* Invoking guix system:: Instantiating a system configuration.
* Defining Services:: Adding new service definitions.
@ -3260,6 +3261,53 @@ password. When @var{auto-login?} is true, log in automatically as
@end deffn
@node Setuid Programs
@subsection Setuid Programs
@cindex setuid programs
Some programs need to run with ``root'' privileges, even when they are
launched by unprivileged users. A notorious example is the
@command{passwd} programs, which can users can run to change their
password, and which requires write access to the @file{/etc/passwd} and
@file{/etc/shadow} files---something normally restricted to root, for
obvious security reasons. To address that, these executables are
@dfn{setuid-root}, meaning that they always run with root privileges
(@pxref{How Change Persona,,, libc, The GNU C Library Reference Manual},
for more info about the setuid mechanisms.)
The store itself @emph{cannot} contain setuid programs: that would be a
security issue since any user on the system can write derivations that
populate the store (@pxref{The Store}). Thus, a different mechanism is
used: instead of changing the setuid bit directly on files that are in
the store, we let the system administrator @emph{declare} which programs
should be setuid root.
The @code{setuid-programs} field of an @code{operating-system}
declaration contains a list of G-expressions denoting the names of
programs to be setuid-root (@pxref{Using the Configuration System}).
For instance, the @command{passwd} program, which is part of the Shadow
package, can be designated by this G-expression (@pxref{G-Expressions}):
@example
#~(string-append #$shadow "/bin/passwd")
@end example
A default set of setuid programs is defined by the
@code{%setuid-programs} variable of the @code{(gnu system)} module.
@defvr {Scheme Variable} %setuid-programs
A list of G-expressions denoting common programs that are setuid-root.
The list includes commands such as @command{passwd}, @command{ping},
@command{su}, and @command{sudo}.
@end defvr
Under the hood, the actual setuid programs are created in the
@file{/run/setuid-programs} directory at system activation time. The
files in this directory refer to the ``real'' binaries, which are in the
store.
@node Initial RAM Disk
@subsection Initial RAM Disk