guix/gnu/system/pam.scm
John Darrington 290ad2243c
gnu: Remove comment which is factually incorrect.
* gnu/system/pam.scm: Remove incorrect comment.
2016-11-06 19:56:43 +01:00

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;;; GNU Guix --- Functional package management for GNU
;;; Copyright © 2013, 2014, 2015, 2016 Ludovic Courtès <ludo@gnu.org>
;;;
;;; This file is part of GNU Guix.
;;;
;;; GNU Guix is free software; you can redistribute it and/or modify it
;;; under the terms of the GNU General Public License as published by
;;; the Free Software Foundation; either version 3 of the License, or (at
;;; your option) any later version.
;;;
;;; GNU Guix is distributed in the hope that it will be useful, but
;;; WITHOUT ANY WARRANTY; without even the implied warranty of
;;; MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the
;;; GNU General Public License for more details.
;;;
;;; You should have received a copy of the GNU General Public License
;;; along with GNU Guix. If not, see <http://www.gnu.org/licenses/>.
(define-module (gnu system pam)
#:use-module (guix records)
#:use-module (guix derivations)
#:use-module (guix gexp)
#:use-module (gnu services)
#:use-module (ice-9 match)
#:use-module (srfi srfi-1)
#:use-module (srfi srfi-9)
#:use-module (srfi srfi-11)
#:use-module (srfi srfi-26)
#:use-module ((guix utils) #:select (%current-system))
#:export (pam-service
pam-service-name
pam-service-account
pam-service-auth
pam-service-password
pam-service-session
pam-entry
pam-entry-control
pam-entry-module
pam-entry-arguments
pam-limits-entry
pam-limits-entry-domain
pam-limits-entry-type
pam-limits-entry-item
pam-limits-entry-value
pam-limits-entry->string
pam-services->directory
unix-pam-service
base-pam-services
pam-root-service-type
pam-root-service))
;;; Commentary:
;;;
;;; Configuration of the pluggable authentication modules (PAM).
;;;
;;; Code:
;; PAM services (see
;; <http://www.linux-pam.org/Linux-PAM-html/sag-configuration-file.html>.)
(define-record-type* <pam-service> pam-service
make-pam-service
pam-service?
(name pam-service-name) ; string
;; The four "management groups".
(account pam-service-account ; list of <pam-entry>
(default '()))
(auth pam-service-auth
(default '()))
(password pam-service-password
(default '()))
(session pam-service-session
(default '())))
(define-record-type* <pam-entry> pam-entry
make-pam-entry
pam-entry?
(control pam-entry-control) ; string
(module pam-entry-module) ; file name
(arguments pam-entry-arguments ; list of string-valued g-expressions
(default '())))
;; PAM limits entries are used by the pam_limits PAM module to set or override
;; limits on system resources for user sessions. The format is specified
;; here: http://linux-pam.org/Linux-PAM-html/sag-pam_limits.html
(define-record-type <pam-limits-entry>
(make-pam-limits-entry domain type item value)
pam-limits-entry?
(domain pam-limits-entry-domain) ; string
(type pam-limits-entry-type) ; symbol
(item pam-limits-entry-item) ; symbol
(value pam-limits-entry-value)) ; symbol or number
(define (pam-limits-entry domain type item value)
"Construct a pam-limits-entry ensuring that the provided values are valid."
(define (valid? value)
(case item
((priority) (number? value))
((nice) (and (number? value)
(>= value -20)
(<= value 19)))
(else (or (and (number? value)
(>= value -1))
(member value '(unlimited infinity))))))
(define items
(list 'core 'data 'fsize
'memlock 'nofile 'rss
'stack 'cpu 'nproc
'as 'maxlogins 'maxsyslogins
'priority 'locks 'sigpending
'msgqueue 'nice 'rtprio))
(when (not (member type '(hard soft both)))
(error "invalid limit type" type))
(when (not (member item items))
(error "invalid limit item" item))
(when (not (valid? value))
(error "invalid limit value" value))
(make-pam-limits-entry domain type item value))
(define (pam-limits-entry->string entry)
"Convert a pam-limits-entry record to a string."
(match entry
(($ <pam-limits-entry> domain type item value)
(string-join (list domain
(if (eq? type 'both)
"-"
(symbol->string type))
(symbol->string item)
(cond
((symbol? value)
(symbol->string value))
(else
(number->string value))))
" "))))
(define (pam-service->configuration service)
"Return the derivation building the configuration file for SERVICE, to be
dumped in /etc/pam.d/NAME, where NAME is the name of SERVICE."
(define (entry->gexp type entry)
(match entry
(($ <pam-entry> control module (arguments ...))
#~(format #t "~a ~a ~a ~a~%"
#$type #$control #$module
(string-join (list #$@arguments))))))
(match service
(($ <pam-service> name account auth password session)
(define builder
#~(begin
(with-output-to-file #$output
(lambda ()
#$@(append (map (cut entry->gexp "account" <>) account)
(map (cut entry->gexp "auth" <>) auth)
(map (cut entry->gexp "password" <>) password)
(map (cut entry->gexp "session" <>) session))
#t))))
(computed-file name builder))))
(define (pam-services->directory services)
"Return the derivation to build the configuration directory to be used as
/etc/pam.d for SERVICES."
(let ((names (map pam-service-name services))
(files (map pam-service->configuration services)))
(define builder
#~(begin
(use-modules (ice-9 match)
(srfi srfi-1))
(mkdir #$output)
(for-each (match-lambda
((name file)
(symlink file (string-append #$output "/" name))))
;; Since <pam-service> objects cannot be compared with
;; 'equal?' since they contain gexps, which contain
;; closures, use 'delete-duplicates' on the build-side
;; instead. See <http://bugs.gnu.org/20037>.
(delete-duplicates '#$(zip names files)))))
(computed-file "pam.d" builder)))
(define %pam-other-services
;; The "other" PAM configuration, which denies everything (see
;; <http://www.linux-pam.org/Linux-PAM-html/sag-configuration-example.html>.)
(let ((deny (pam-entry
(control "required")
(module "pam_deny.so"))))
(pam-service
(name "other")
(account (list deny))
(auth (list deny))
(password (list deny))
(session (list deny)))))
(define unix-pam-service
(let ((unix (pam-entry
(control "required")
(module "pam_unix.so")))
(env (pam-entry ; to honor /etc/environment.
(control "required")
(module "pam_env.so"))))
(lambda* (name #:key allow-empty-passwords? motd)
"Return a standard Unix-style PAM service for NAME. When
ALLOW-EMPTY-PASSWORDS? is true, allow empty passwords. When MOTD is true, it
should be a file-like object used as the message-of-the-day."
;; See <http://www.linux-pam.org/Linux-PAM-html/sag-configuration-example.html>.
(let ((name* name))
(pam-service
(name name*)
(account (list unix))
(auth (list (if allow-empty-passwords?
(pam-entry
(control "required")
(module "pam_unix.so")
(arguments '("nullok")))
unix)))
(password (list (pam-entry
(control "required")
(module "pam_unix.so")
;; Store SHA-512 encrypted passwords in /etc/shadow.
(arguments '("sha512" "shadow")))))
(session (if motd
(list env unix
(pam-entry
(control "optional")
(module "pam_motd.so")
(arguments
(list #~(string-append "motd=" #$motd)))))
(list env unix))))))))
(define (rootok-pam-service command)
"Return a PAM service for COMMAND such that 'root' does not need to
authenticate to run COMMAND."
(let ((unix (pam-entry
(control "required")
(module "pam_unix.so"))))
(pam-service
(name command)
(account (list unix))
(auth (list (pam-entry
(control "sufficient")
(module "pam_rootok.so"))))
(password (list unix))
(session (list unix)))))
(define* (base-pam-services #:key allow-empty-passwords?)
"Return the list of basic PAM services everyone would want."
;; TODO: Add other Shadow programs?
(append (list %pam-other-services)
;; These programs are setuid-root.
(map (cut unix-pam-service <>
#:allow-empty-passwords? allow-empty-passwords?)
'("su" "passwd" "sudo"))
;; These programs are not setuid-root, and we want root to be able
;; to run them without having to authenticate (notably because
;; 'useradd' and 'groupadd' are run during system activation.)
(map rootok-pam-service
'("useradd" "userdel" "usermod"
"groupadd" "groupdel" "groupmod"))))
;;;
;;; PAM root service.
;;;
;; Overall PAM configuration: a list of services, plus a procedure that takes
;; one <pam-service> and returns a <pam-service>. The procedure is used to
;; implement cross-cutting concerns such as the use of the 'elogind.so'
;; session module that keeps track of logged-in users.
(define-record-type* <pam-configuration>
pam-configuration make-pam-configuration? pam-configuration?
(services pam-configuration-services) ;list of <pam-service>
(transform pam-configuration-transform)) ;procedure
(define (/etc-entry config)
"Return the /etc/pam.d entry corresponding to CONFIG."
(match config
(($ <pam-configuration> services transform)
(let ((services (map transform services)))
`(("pam.d" ,(pam-services->directory services)))))))
(define (extend-configuration initial extensions)
"Extend INITIAL with NEW."
(let-values (((services procs)
(partition pam-service? extensions)))
(pam-configuration
(services (append (pam-configuration-services initial)
services))
(transform (apply compose
(pam-configuration-transform initial)
procs)))))
(define pam-root-service-type
(service-type (name 'pam)
(extensions (list (service-extension etc-service-type
/etc-entry)))
;; Arguments include <pam-service> as well as procedures.
(compose concatenate)
(extend extend-configuration)))
(define* (pam-root-service base #:key (transform identity))
"The \"root\" PAM service, which collects <pam-service> instance and turns
them into a /etc/pam.d directory, including the <pam-service> listed in BASE.
TRANSFORM is a procedure that takes a <pam-service> and returns a
<pam-service>. It can be used to implement cross-cutting concerns that affect
all the PAM services."
(service pam-root-service-type
(pam-configuration (services base)
(transform transform))))