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services: Prevent following symlinks during activation.
This addresses a potential security issue, where a compromised service could trick the activation code in changing the permissions, owner and group of arbitrary files. However, this patch is currently only a partial fix, due to a TOCTTOU (time-of-check to time-of-use) race, which can be fixed once guile has bindings to openat and friends. Fixes: <https://lists.gnu.org/archive/html/guix-devel/2021-01/msg00388.html> * gnu/build/activation.scm: new procedure 'mkdir-p/perms'. * gnu/services/authentication.scm (%nslcd-activation, nslcd-service-type): use new procedure. * gnu/services/cups.scm (%cups-activation): likewise. * gnu/services/dbus.scm (dbus-activation): likewise. * gnu/services/dns.scm (knot-activation): likewise. Signed-off-by: Ludovic Courtès <ludo@gnu.org>
This commit is contained in:
Maxime Devos
Ludovic Courtès
parent
1a1d0fe505
commit
520bac7ed0
5 changed files with 96 additions and 45 deletions
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@ -1,6 +1,11 @@
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;;; GNU Guix --- Functional package management for GNU
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;;; Copyright © 2013, 2014, 2015, 2016, 2017, 2018, 2019, 2020, 2021 Ludovic Courtès <ludo@gnu.org>
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;;; Copyright © 2015 Mark H Weaver <mhw@netris.org>
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;;; Copyright © 2012, 2013, 2014, 2015, 2016, 2017, 2018, 2019, 2020, 2021 Ludovic Courtès <ludo@gnu.org>
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;;; Copyright © 2013 Nikita Karetnikov <nikita@karetnikov.org>
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;;; Copyright © 2013 Andreas Enge <andreas@enge.fr>
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;;; Copyright © 2015, 2018 Mark H Weaver <mhw@netris.org>
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;;; Copyright © 2018 Arun Isaac <arunisaac@systemreboot.net>
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;;; Copyright © 2018, 2019 Ricardo Wurmus <rekado@elephly.net>
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;;; Copyright © 2021 Maxime Devos <maximedevos@telenet.be>
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;;;
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;;; This file is part of GNU Guix.
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;;;
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@ -37,7 +42,8 @@ (define-module (gnu build activation)
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activate-modprobe
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activate-firmware
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activate-ptrace-attach
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activate-current-system))
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activate-current-system
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mkdir-p/perms))
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;;; Commentary:
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;;;
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@ -55,6 +61,47 @@ (define %skeleton-directory
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(define (dot-or-dot-dot? file)
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(member file '("." "..")))
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;; Based upon mkdir-p from (guix build utils)
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(define (verify-not-symbolic dir)
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"Verify DIR or its ancestors aren't symbolic links."
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(define absolute?
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(string-prefix? "/" dir))
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(define not-slash
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(char-set-complement (char-set #\/)))
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(define (verify-component file)
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(unless (eq? 'directory (stat:type (lstat file)))
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(error "file name component is not a directory" dir)))
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(let loop ((components (string-tokenize dir not-slash))
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(root (if absolute?
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""
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".")))
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(match components
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((head tail ...)
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(let ((file (string-append root "/" head)))
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(catch 'system-error
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(lambda ()
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(verify-component file)
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(loop tail file))
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(lambda args
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(if (= ENOENT (system-error-errno args))
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#t
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(apply throw args))))))
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(() #t))))
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;; TODO: the TOCTTOU race can be addressed once guile has bindings
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;; for fstatat, openat and friends.
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(define (mkdir-p/perms directory owner bits)
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"Create the directory DIRECTORY and all its ancestors.
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Verify no component of DIRECTORY is a symbolic link.
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Warning: this is currently suspect to a TOCTTOU race!"
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(verify-not-symbolic directory)
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(mkdir-p directory)
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(chown directory (passwd:uid owner) (passwd:gid owner))
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(chmod directory bits))
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(define* (copy-account-skeletons home
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#:key
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(directory %skeleton-directory)
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@ -1,6 +1,7 @@
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;;; GNU Guix --- Functional package management for GNU
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;;; Copyright © 2018 Danny Milosavljevic <dannym@scratchpost.org>
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;;; Copyright © 2018, 2019 Ricardo Wurmus <rekado@elephly.net>
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;;; Copyright © 2021 Maxime Devos <maximedevos@telenet.be>
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;;;
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;;; This file is part of GNU Guix.
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;;;
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@ -31,6 +32,7 @@ (define-module (gnu services authentication)
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#:use-module (guix gexp)
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#:use-module (guix records)
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#:use-module (guix packages)
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#:use-module (guix modules)
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#:use-module (ice-9 match)
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#:use-module (srfi srfi-1)
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#:use-module (srfi srfi-26)
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@ -521,6 +523,16 @@ (module pam-ldap-module))))
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(define (pam-ldap-pam-services config)
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(list (pam-ldap-pam-service config)))
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(define %nslcd-activation
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(with-imported-modules (source-module-closure '((gnu build activation)))
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#~(begin
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(use-modules (gnu build activation))
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(let ((rundir "/var/run/nslcd")
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(user (getpwnam "nslcd")))
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(mkdir-p/perms rundir user #o755)
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(when (file-exists? "/etc/nslcd.conf")
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(chmod "/etc/nslcd.conf" #o400))))))
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(define nslcd-service-type
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(service-type
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(name 'nslcd)
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@ -531,15 +543,7 @@ (define nslcd-service-type
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(service-extension etc-service-type
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nslcd-etc-service)
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(service-extension activation-service-type
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(const #~(begin
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(use-modules (guix build utils))
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(let ((rundir "/var/run/nslcd")
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(user (getpwnam "nslcd")))
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(mkdir-p rundir)
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(chown rundir (passwd:uid user) (passwd:gid user))
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(chmod rundir #o755)
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(when (file-exists? "/etc/nslcd.conf")
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(chmod "/etc/nslcd.conf" #o400))))))
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(const %nslcd-activation))
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(service-extension pam-root-service-type
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pam-ldap-pam-services)
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(service-extension nscd-service-type
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@ -4,6 +4,7 @@
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;;; Copyright © 2018 Ricardo Wurmus <rekado@elephly.net>
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;;; Copyright © 2019 Alex Griffin <a@ajgrf.com>
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;;; Copyright © 2019 Tobias Geerinckx-Rice <me@tobias.gr>
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;;; Copyright © 2021 Maxime Devos <maximedevos@telenet.be>
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;;;
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;;; This file is part of GNU Guix.
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;;;
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@ -31,6 +32,7 @@ (define-module (gnu services cups)
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#:use-module (guix packages)
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#:use-module (guix records)
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#:use-module (guix gexp)
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#:use-module (guix modules)
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#:use-module (ice-9 match)
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#:use-module ((srfi srfi-1) #:select (append-map find))
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#:export (cups-service-type
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@ -871,13 +873,11 @@ (define-configuration opaque-cups-configuration
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(define %cups-activation
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;; Activation gexp.
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(with-imported-modules '((guix build utils))
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(with-imported-modules (source-module-closure '((gnu build activation)
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(guix build utils)))
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#~(begin
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(use-modules (guix build utils))
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(define (mkdir-p/perms directory owner perms)
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(mkdir-p directory)
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(chown directory (passwd:uid owner) (passwd:gid owner))
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(chmod directory perms))
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(use-modules (gnu build activation)
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(guix build utils))
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(define (build-subject parameters)
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(string-concatenate
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(map (lambda (pair)
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@ -1,6 +1,7 @@
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;;; GNU Guix --- Functional package management for GNU
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;;; Copyright © 2013, 2014, 2015, 2016, 2017, 2019, 2020 Ludovic Courtès <ludo@gnu.org>
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;;; Copyright © 2015 Sou Bunnbu <iyzsong@gmail.com>
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;;; Copyright © 2021 Maxime Devos <maximedevos@telenet.be>
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;;;
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;;; This file is part of GNU Guix.
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;;;
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@ -28,6 +29,7 @@ (define-module (gnu services dbus)
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#:use-module (guix gexp)
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#:use-module ((guix packages) #:select (package-name))
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#:use-module (guix records)
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#:use-module (guix modules)
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#:use-module (srfi srfi-1)
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#:use-module (ice-9 match)
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#:export (dbus-configuration
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@ -161,24 +163,23 @@ (define dbus-setuid-programs
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(define (dbus-activation config)
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"Return an activation gexp for D-Bus using @var{config}."
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(with-imported-modules (source-module-closure
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'((gnu build activation)
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(guix build utils)))
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#~(begin
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(use-modules (guix build utils))
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(mkdir-p "/var/run/dbus")
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(use-modules (gnu build activation)
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(guix build utils))
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(let ((user (getpwnam "messagebus")))
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(chown "/var/run/dbus"
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(passwd:uid user) (passwd:gid user))
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;; This directory contains the daemon's socket so it must be
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;; world-readable.
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(chmod "/var/run/dbus" #o755))
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(mkdir-p/perms "/var/run/dbus" user #o755))
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(unless (file-exists? "/etc/machine-id")
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(format #t "creating /etc/machine-id...~%")
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(invoke (string-append #$(dbus-configuration-dbus config)
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"/bin/dbus-uuidgen")
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"--ensure=/etc/machine-id"))))
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"--ensure=/etc/machine-id")))))
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(define dbus-shepherd-service
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(match-lambda
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@ -2,6 +2,7 @@
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;;; Copyright © 2017 Julien Lepiller <julien@lepiller.eu>
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;;; Copyright © 2018 Oleg Pykhalov <go.wigust@gmail.com>
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;;; Copyright © 2020 Pierre Langlois <pierre.langlois@gmx.com>
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;;; Copyright © 2021 Maxime Devos <maximedevos@telenet.be>
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;;;
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;;; This file is part of GNU Guix.
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;;;
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@ -28,6 +29,7 @@ (define-module (gnu services dns)
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#:use-module (guix packages)
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#:use-module (guix records)
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#:use-module (guix gexp)
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#:use-module (guix modules)
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#:use-module (srfi srfi-1)
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#:use-module (srfi srfi-26)
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#:use-module (srfi srfi-34)
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@ -607,17 +609,14 @@ (define %knot-accounts
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(shell (file-append shadow "/sbin/nologin")))))
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(define (knot-activation config)
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(with-imported-modules (source-module-closure '((gnu build activation)))
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#~(begin
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(use-modules (guix build utils))
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(define (mkdir-p/perms directory owner perms)
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(mkdir-p directory)
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(chown directory (passwd:uid owner) (passwd:gid owner))
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(chmod directory perms))
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(use-modules (gnu build activation))
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(mkdir-p/perms #$(knot-configuration-run-directory config)
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(getpwnam "knot") #o755)
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(mkdir-p/perms "/var/lib/knot" (getpwnam "knot") #o755)
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(mkdir-p/perms "/var/lib/knot/keys" (getpwnam "knot") #o755)
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(mkdir-p/perms "/var/lib/knot/keys/keys" (getpwnam "knot") #o755)))
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(mkdir-p/perms "/var/lib/knot/keys/keys" (getpwnam "knot") #o755))))
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(define (knot-shepherd-service config)
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(let* ((config-file (knot-config-file config))
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