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+;;; GNU Guix --- Functional package management for GNU
+;;; Copyright © 2019 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 build accounts)
+ #:use-module (guix records)
+ #:use-module (guix combinators)
+ #:use-module (gnu system accounts)
+ #:use-module (srfi srfi-1)
+ #:use-module (srfi srfi-11)
+ #:use-module (srfi srfi-19)
+ #:use-module (srfi srfi-26)
+ #:use-module (ice-9 match)
+ #:use-module (ice-9 vlist)
+ #:use-module (ice-9 rdelim)
+ #:export (password-entry
+ password-entry?
+ password-entry-name
+ password-entry-uid
+ password-entry-gid
+ password-entry-real-name
+ password-entry-directory
+ password-entry-shell
+
+ shadow-entry
+ shadow-entry?
+ shadow-entry-name
+ shadow-entry-minimum-change-period
+ shadow-entry-maximum-change-period
+ shadow-entry-change-warning-time
+ shadow-entry-maximum-inactivity
+ shadow-entry-expiration
+
+ group-entry
+ group-entry?
+ group-entry-name
+ group-entry-gid
+ group-entry-members
+
+ write-group
+ write-passwd
+ write-shadow
+ read-group
+ read-passwd
+ read-shadow
+
+ %id-min
+ %id-max
+ %system-id-min
+ %system-id-max
+
+ user+group-databases))
+
+;;; Commentary:
+;;;
+;;; This modules provides functionality equivalent to the C library's
+;;; <shadow.h>, <pwd.h>, and <grp.h> routines, as well as a subset of the
+;;; functionality of the Shadow command-line tools. It can parse and write
+;;; /etc/passwd, /etc/shadow, and /etc/group. It can also take care of UID
+;;; and GID allocation in a way similar to what 'useradd' does.
+;;;
+;;; The benefit is twofold: less code is involved, and the ID allocation
+;;; strategy and state preservation is made explicit.
+;;;
+;;; Code:
+
+
+;;;
+;;; Machinery to define user and group databases.
+;;;
+
+(define-syntax serialize-field
+ (syntax-rules (serialization)
+ ((_ entry (field get (serialization ->string string->) _ ...))
+ (->string (get entry)))
+ ((_ entry (field get _ ...))
+ (get entry))))
+
+(define-syntax deserialize-field
+ (syntax-rules (serialization)
+ ((_ str (field get (serialization ->string string->) _ ...))
+ (string-> str))
+ ((_ str (field get _ ...))
+ str)))
+
+(define-syntax let/fields
+ (syntax-rules ()
+ ((_ (((name get attributes ...) rest ...) lst) body ...)
+ (let ((l lst))
+ (let ((name (deserialize-field (car l)
+ (name get attributes ...))))
+ (let/fields ((rest ...) (cdr l)) body ...))))
+ ((_ (() lst) body ...)
+ (begin body ...))))
+
+(define-syntax define-database-entry
+ (syntax-rules (serialization)
+ "Define a record data type, as per 'define-record-type*', with additional
+information on how to serialize and deserialize the whole database as well as
+each field."
+ ((_ <record> record make-record record?
+ (serialization separator entry->string string->entry)
+ fields ...)
+ (let-syntax ((field-name
+ (syntax-rules ()
+ ((_ (name _ (... ...))) name))))
+ (define-record-type* <record> record make-record
+ record?
+ fields ...)
+
+ (define (entry->string entry)
+ (string-join (list (serialize-field entry fields) ...)
+ (string separator)))
+
+ (define (string->entry str)
+ (let/fields ((fields ...) (string-split str #\:))
+ (make-record (field-name fields) ...)))))))
+
+
+(define number->string*
+ (match-lambda
+ ((? number? number) (number->string number))
+ (_ "")))
+
+(define (false-if-string=? false-string)
+ (lambda (str)
+ (if (string=? str false-string)
+ #f
+ str)))
+
+(define (string-if-false str)
+ (lambda (obj)
+ (if (not obj) str obj)))
+
+(define (comma-separated->list str)
+ (string-tokenize str (char-set-complement (char-set #\,))))
+
+(define (list->comma-separated lst)
+ (string-join lst ","))
+
+
+;;;
+;;; Database definitions.
+;;;
+
+(define-database-entry <password-entry> ;<pwd.h>
+ password-entry make-password-entry
+ password-entry?
+ (serialization #\: password-entry->string string->password-entry)
+
+ (name password-entry-name)
+ (password password-entry-password
+ (serialization (const "x") (const #f))
+ (default "x"))
+ (uid password-entry-uid
+ (serialization number->string string->number))
+ (gid password-entry-gid
+ (serialization number->string string->number))
+ (real-name password-entry-real-name
+ (default ""))
+ (directory password-entry-directory)
+ (shell password-entry-shell
+ (default "/bin/sh")))
+
+(define-database-entry <shadow-entry> ;<shadow.h>
+ shadow-entry make-shadow-entry
+ shadow-entry?
+ (serialization #\: shadow-entry->string string->shadow-entry)
+
+ (name shadow-entry-name) ;string
+ (password shadow-entry-password ;string | #f
+ (serialization (string-if-false "!")
+ (false-if-string=? "!"))
+ (default #f))
+ (last-change shadow-entry-last-change ;days since 1970-01-01
+ (serialization number->string* string->number)
+ (default 0))
+ (minimum-change-period shadow-entry-minimum-change-period
+ (serialization number->string* string->number)
+ (default #f)) ;days | #f
+ (maximum-change-period shadow-entry-maximum-change-period
+ (serialization number->string* string->number)
+ (default #f)) ;days | #f
+ (change-warning-time shadow-entry-change-warning-time
+ (serialization number->string* string->number)
+ (default #f)) ;days | #f
+ (maximum-inactivity shadow-entry-maximum-inactivity
+ (serialization number->string* string->number)
+ (default #f)) ;days | #f
+ (expiration shadow-entry-expiration
+ (serialization number->string* string->number)
+ (default #f)) ;days since 1970-01-01 | #f
+ (flags shadow-entry-flags ;"reserved"
+ (serialization number->string* string->number)
+ (default #f)))
+
+(define-database-entry <group-entry> ;<grp.h>
+ group-entry make-group-entry
+ group-entry?
+ (serialization #\: group-entry->string string->group-entry)
+
+ (name group-entry-name)
+ (password group-entry-password
+ (serialization (string-if-false "x")
+ (false-if-string=? "x"))
+ (default #f))
+ (gid group-entry-gid
+ (serialization number->string string->number))
+ (members group-entry-members
+ (serialization list->comma-separated comma-separated->list)
+ (default '())))
+
+(define (database-writer file mode entry->string)
+ (lambda* (entries #:optional (file-or-port file))
+ "Write ENTRIES to FILE-OR-PORT. When FILE-OR-PORT is a file name, write
+to it atomically and set the appropriate permissions."
+ (define (write-entries port)
+ (for-each (lambda (entry)
+ (display (entry->string entry) port)
+ (newline port))
+ entries))
+
+ (if (port? file-or-port)
+ (write-entries file-or-port)
+ (let* ((template (string-append file-or-port ".XXXXXX"))
+ (port (mkstemp! template)))
+ (dynamic-wind
+ (const #t)
+ (lambda ()
+ (chmod port mode)
+ (write-entries port)
+ (rename-file template file-or-port))
+ (lambda ()
+ (close-port port)
+ (when (file-exists? template)
+ (delete-file template))))))))
+
+(define write-passwd
+ (database-writer "/etc/passwd" #o644 password-entry->string))
+(define write-shadow
+ (database-writer "/etc/shadow" #o600 shadow-entry->string))
+(define write-group
+ (database-writer "/etc/group" #o644 group-entry->string))
+
+(define (database-reader file string->entry)
+ (lambda* (#:optional (file-or-port file))
+ (define (read-entries port)
+ (let loop ((entries '()))
+ (match (read-line port)
+ ((? eof-object?)
+ (reverse entries))
+ (line
+ (loop (cons (string->entry line) entries))))))
+
+ (if (port? file-or-port)
+ (read-entries file-or-port)
+ (call-with-input-file file-or-port
+ read-entries))))
+
+(define read-passwd
+ (database-reader "/etc/passwd" string->password-entry))
+(define read-shadow
+ (database-reader "/etc/shadow" string->shadow-entry))
+(define read-group
+ (database-reader "/etc/group" string->group-entry))
+
+
+;;;
+;;; Building databases.
+;;;
+
+(define-record-type* <allocation>
+ allocation make-allocation
+ allocation?
+ (ids allocation-ids (default vlist-null))
+ (next-id allocation-next-id (default %id-min))
+ (next-system-id allocation-next-system-id (default %system-id-max)))
+
+;; Trick to avoid name clashes...
+(define-syntax %allocation (identifier-syntax allocation))
+
+;; Minimum and maximum UIDs and GIDs (from find_new_uid.c and find_new_gid.c
+;; in Shadow.)
+(define %id-min 1000)
+(define %id-max 60000)
+
+(define %system-id-min 100)
+(define %system-id-max 999)
+
+(define (system-id? id)
+ (and (> id %system-id-min)
+ (<= id %system-id-max)))
+
+(define (user-id? id)
+ (and (>= id %id-min)
+ (< id %id-max)))
+
+(define* (allocate-id assignment #:key system?)
+ "Return two values: a newly allocated ID, and an updated <allocation> record
+based on ASSIGNMENT. If SYSTEM? is true, return a system ID."
+ (define next
+ ;; Return the next available ID, looping if necessary.
+ (if system?
+ (lambda (id)
+ (let ((next-id (- id 1)))
+ (if (< next-id %system-id-min)
+ %system-id-max
+ next-id)))
+ (lambda (id)
+ (let ((next-id (+ id 1)))
+ (if (>= next-id %id-max)
+ %id-min
+ next-id)))))
+
+ (let loop ((id (if system?
+ (allocation-next-system-id assignment)
+ (allocation-next-id assignment))))
+ (if (vhash-assv id (allocation-ids assignment))
+ (loop (next id))
+ (let ((taken (vhash-consv id #t (allocation-ids assignment))))
+ (values (if system?
+ (allocation (inherit assignment)
+ (next-system-id (next id))
+ (ids taken))
+ (allocation (inherit assignment)
+ (next-id (next id))
+ (ids taken)))
+ id)))))
+
+(define* (reserve-ids allocation ids #:key (skip? #t))
+ "Mark the numbers listed in IDS as reserved in ALLOCATION. When SKIP? is
+true, start allocation after the highest (or lowest, depending on whether it's
+a system ID allocation) number among IDS."
+ (%allocation
+ (inherit allocation)
+ (next-id (if skip?
+ (+ (reduce max
+ (- (allocation-next-id allocation) 1)
+ (filter user-id? ids))
+ 1)
+ (allocation-next-id allocation)))
+ (next-system-id
+ (if skip?
+ (- (reduce min
+ (+ 1 (allocation-next-system-id allocation))
+ (filter system-id? ids))
+ 1)
+ (allocation-next-system-id allocation)))
+ (ids (fold (cut vhash-consv <> #t <>)
+ (allocation-ids allocation)
+ ids))))
+
+(define (allocated? allocation id)
+ "Return true if ID is already allocated as part of ALLOCATION."
+ (->bool (vhash-assv id (allocation-ids allocation))))
+
+(define (lookup-procedure lst key)
+ "Return a lookup procedure for the elements of LST, calling KEY to obtain
+the key of each element."
+ (let ((table (fold (lambda (obj table)
+ (vhash-cons (key obj) obj table))
+ vlist-null
+ lst)))
+ (lambda (key)
+ (match (vhash-assoc key table)
+ (#f #f)
+ ((_ . value) value)))))
+
+(define* (allocate-groups groups members
+ #:optional (current-groups '()))
+ "Return a list of group entries for GROUPS, a list of <user-group>. Members
+for each group are taken from MEMBERS, a vhash that maps group names to member
+names. GIDs and passwords found in CURRENT-GROUPS, a list of group entries,
+are reused."
+ (define gids
+ ;; Mark all the currently-used GIDs and the explicitly requested GIDs as
+ ;; reserved.
+ (reserve-ids (reserve-ids (allocation)
+ (map group-entry-gid current-groups))
+ (filter-map user-group-id groups)
+ #:skip? #f))
+
+ (define previous-entry
+ (lookup-procedure current-groups group-entry-name))
+
+ (reverse
+ (fold2 (lambda (group result allocation)
+ (let ((name (user-group-name group))
+ (password (user-group-password group))
+ (requested-id (user-group-id group))
+ (system? (user-group-system? group)))
+ (let*-values (((previous)
+ (previous-entry name))
+ ((allocation id)
+ (cond
+ ((number? requested-id)
+ (values (reserve-ids allocation
+ (list requested-id))
+ requested-id))
+ (previous
+ (values allocation
+ (group-entry-gid previous)))
+ (else
+ (allocate-id allocation
+ #:system? system?)))))
+ (values (cons (group-entry
+ (name name)
+ (password
+ (if previous
+ (group-entry-password previous)
+ password))
+ (gid id)
+ (members (vhash-fold* cons '() name members)))
+ result)
+ allocation))))
+ '()
+ gids
+ groups)))
+
+(define* (allocate-passwd users groups #:optional (current-passwd '()))
+ "Return a list of password entries for USERS, a list of <user-account>.
+Take GIDs from GROUPS, a list of group entries. Reuse UIDs from
+CURRENT-PASSWD, a list of password entries, when possible; otherwise allocate
+new UIDs."
+ (define uids
+ (reserve-ids (reserve-ids (allocation)
+ (map password-entry-uid current-passwd))
+ (filter-map user-account-uid users)
+ #:skip? #f))
+
+ (define previous-entry
+ (lookup-procedure current-passwd password-entry-name))
+
+ (define (group-id name)
+ (or (any (lambda (entry)
+ (and (string=? (group-entry-name entry) name)
+ (group-entry-gid entry)))
+ groups)
+ (error "group not found" name)))
+
+ (reverse
+ (fold2 (lambda (user result allocation)
+ (let ((name (user-account-name user))
+ (requested-id (user-account-uid user))
+ (group (user-account-group user))
+ (real-name (user-account-comment user))
+ (directory (user-account-home-directory user))
+ (shell (user-account-shell user))
+ (system? (user-account-system? user)))
+ (let*-values (((previous)
+ (previous-entry name))
+ ((allocation id)
+ (cond
+ ((number? requested-id)
+ (values (reserve-ids allocation
+ (list requested-id))
+ requested-id))
+ (previous
+ (values allocation
+ (password-entry-uid previous)))
+ (else
+ (allocate-id allocation
+ #:system? system?)))))
+ (values (cons (password-entry
+ (name name)
+ (uid id)
+ (directory directory)
+ (gid (if (number? group) group (group-id group)))
+ (real-name (if previous
+ (password-entry-real-name previous)
+ real-name))
+ (shell (if previous
+ (password-entry-shell previous)
+ shell)))
+ result)
+ allocation))))
+ '()
+ uids
+ users)))
+
+(define* (days-since-epoch #:optional (current-time current-time))
+ "Return the number of days elapsed since the 1st of January, 1970."
+ (let* ((now (current-time time-utc))
+ (epoch (make-time time-utc 0 0))
+ (diff (time-difference now epoch)))
+ (quotient (time-second diff) (* 24 3600))))
+
+(define* (passwd->shadow users passwd #:optional (current-shadow '())
+ #:key (current-time current-time))
+ "Return a list of shadow entries for the password entries listed in PASSWD.
+Reuse shadow entries from CURRENT-SHADOW when they exist, and take the initial
+password from USERS."
+ (define previous-entry
+ (lookup-procedure current-shadow shadow-entry-name))
+
+ (define now
+ (days-since-epoch current-time))
+
+ (map (lambda (user passwd)
+ (or (previous-entry (password-entry-name passwd))
+ (shadow-entry (name (password-entry-name passwd))
+ (password (user-account-password user))
+ (last-change now))))
+ users passwd))
+
+(define (empty-if-not-found thunk)
+ "Call THUNK and return the empty list if that throws to ENOENT."
+ (catch 'system-error
+ thunk
+ (lambda args
+ (if (= ENOENT (system-error-errno args))
+ '()
+ (apply throw args)))))
+
+(define* (user+group-databases users groups
+ #:key
+ (current-passwd
+ (empty-if-not-found read-passwd))
+ (current-groups
+ (empty-if-not-found read-group))
+ (current-shadow
+ (empty-if-not-found read-shadow))
+ (current-time current-time))
+ "Return three values: the list of group entries, the list of password
+entries, and the list of shadow entries corresponding to USERS and GROUPS.
+Preserve stateful bits from CURRENT-PASSWD, CURRENT-GROUPS, and
+CURRENT-SHADOW: UIDs, GIDs, passwords, user shells, etc."
+ (define members
+ ;; Map group name to user names.
+ (fold (lambda (user members)
+ (fold (cute vhash-cons <> (user-account-name user) <>)
+ members
+ (user-account-supplementary-groups user)))
+ vlist-null
+ users))
+
+ (define group-entries
+ (allocate-groups groups members current-groups))
+
+ (define passwd-entries
+ (allocate-passwd users group-entries current-passwd))
+
+ (define shadow-entries
+ (passwd->shadow users passwd-entries current-shadow
+ #:current-time current-time))
+
+ (values group-entries passwd-entries shadow-entries))
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