etc: Add SELinux policy for the daemon.
* etc/guix-daemon.cil.in: New file. * Makefile.am (dist_selinux_policy_DATA): Define it. * configure.ac: Handle --with-selinux-policy-dir. * doc/guix.texi (SELinux Support): New section.
This commit is contained in:
Ricardo Wurmus
Ricardo Wurmus
parent
5ac1143dc4
commit
b617a9fe23
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@ -446,6 +446,9 @@ dist_zshcompletion_DATA = etc/completion/zsh/_guix
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# Fish completion file.
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dist_fishcompletion_DATA = etc/completion/fish/guix.fish
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# SELinux policy
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dist_selinux_policy_DATA = etc/guix-daemon.cil
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EXTRA_DIST = \
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HACKING \
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ROADMAP \
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@ -54,6 +54,13 @@ AC_ARG_WITH([fish-completion-dir],
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[fishcompletiondir='${datadir}/fish/vendor_completions.d'])
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AC_SUBST([fishcompletiondir])
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AC_ARG_WITH([selinux-policy-dir],
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AC_HELP_STRING([--with-selinux-policy-dir=DIR],
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[name of the SELinux policy directory]),
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[selinux_policydir="$withval"],
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[selinux_policydir='${datadir}/selinux/'])
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AC_SUBST([selinux_policydir])
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dnl Better be verbose.
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AC_MSG_CHECKING([for the store directory])
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AC_MSG_RESULT([$storedir])
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@ -272,6 +279,7 @@ esac
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AC_CONFIG_FILES([Makefile
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po/guix/Makefile.in
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po/packages/Makefile.in
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etc/guix-daemon.cil
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guix/config.scm])
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AC_CONFIG_FILES([test-env:build-aux/test-env.in], [chmod +x test-env])
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@ -21,7 +21,7 @@ Copyright @copyright{} 2015, 2016 Mathieu Lirzin@*
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Copyright @copyright{} 2014 Pierre-Antoine Rault@*
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Copyright @copyright{} 2015 Taylan Ulrich Bayırlı/Kammer@*
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Copyright @copyright{} 2015, 2016, 2017 Leo Famulari@*
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Copyright @copyright{} 2015, 2016, 2017 Ricardo Wurmus@*
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Copyright @copyright{} 2015, 2016, 2017, 2018 Ricardo Wurmus@*
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Copyright @copyright{} 2016 Ben Woodcroft@*
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Copyright @copyright{} 2016, 2017 Chris Marusich@*
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Copyright @copyright{} 2016, 2017 Efraim Flashner@*
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@ -123,6 +123,7 @@ Setting Up the Daemon
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* Build Environment Setup:: Preparing the isolated build environment.
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* Daemon Offload Setup:: Offloading builds to remote machines.
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* SELinux Support:: Using an SELinux policy for the daemon.
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Package Management
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@ -754,6 +755,7 @@ the daemon to download pre-built binaries.
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@menu
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* Build Environment Setup:: Preparing the isolated build environment.
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* Daemon Offload Setup:: Offloading builds to remote machines.
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* SELinux Support:: Using an SELinux policy for the daemon.
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@end menu
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@node Build Environment Setup
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@ -1081,6 +1083,92 @@ main node:
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@end example
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@node SELinux Support
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@subsection SELinux Support
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@cindex SELinux, daemon policy
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@cindex mandatory access control, SELinux
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@cindex security, guix-daemon
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Guix includes an SELinux policy file at @file{etc/guix-daemon.cil} that
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can be installed on a system where SELinux is enabled, in order to label
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Guix files and to specify the expected behavior of the daemon. Since
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GuixSD does not provide an SELinux base policy, the daemon policy cannot
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be used on GuixSD.
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@subsubsection Installing the SELinux policy
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@cindex SELinux, policy installation
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To install the policy run this command as root:
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@example
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semodule -i etc/guix-daemon.cil
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@end example
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Then relabel the file system with @code{restorecon} or by a different
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mechanism provided by your system.
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Once the policy is installed, the file system has been relabeled, and
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the daemon has been restarted, it should be running in the
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@code{guix_daemon_t} context. You can confirm this with the following
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command:
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@example
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ps -Zax | grep guix-daemon
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@end example
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Monitor the SELinux log files as you run a command like @code{guix build
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hello} to convince yourself that SELinux permits all necessary
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operations.
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@subsubsection Limitations
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@cindex SELinux, limitations
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This policy is not perfect. Here is a list of limitations or quirks
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that should be considered when deploying the provided SELinux policy for
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the Guix daemon.
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@enumerate
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@item
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@code{guix_daemon_socket_t} isn’t actually used. None of the socket
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operations involve contexts that have anything to do with
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@code{guix_daemon_socket_t}. It doesn’t hurt to have this unused label,
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but it would be preferrable to define socket rules for only this label.
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@item
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@code{guix gc} cannot access arbitrary links to profiles. By design,
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the file label of the destination of a symlink is independent of the
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file label of the link itself. Although all profiles under
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$localstatedir are labelled, the links to these profiles inherit the
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label of the directory they are in. For links in the user’s home
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directory this will be @code{user_home_t}. But for links from the root
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user’s home directory, or @file{/tmp}, or the HTTP server’s working
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directory, etc, this won’t work. @code{guix gc} would be prevented from
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reading and following these links.
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@item
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The daemon’s feature to listen for TCP connections might no longer work.
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This might require extra rules, because SELinux treats network sockets
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differently from files.
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@item
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Currently all files with a name matching the regular expression
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@code{/gnu/store/.+-(guix-.+|profile)/bin/guix-daemon} are assigned the
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label @code{guix_daemon_exec_t}; this means that @emph{any} file with
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that name in any profile would be permitted to run in the
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@code{guix_daemon_t} domain. This is not ideal. An attacker could
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build a package that provides this executable and convince a user to
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install and run it, which lifts it into the @code{guix_daemon_t} domain.
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At that point SELinux could not prevent it from accessing files that are
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allowed for processes in that domain.
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We could generate a much more restrictive policy at installation time,
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so that only the @emph{exact} file name of the currently installed
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@code{guix-daemon} executable would be labelled with
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@code{guix_daemon_exec_t}, instead of using a broad regular expression.
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The downside is that root would have to install or upgrade the policy at
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installation time whenever the Guix package that provides the
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effectively running @code{guix-daemon} executable is upgraded.
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@end enumerate
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@node Invoking guix-daemon
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@section Invoking @command{guix-daemon}
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@ -0,0 +1,285 @@
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; -*- lisp -*-
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;;; GNU Guix --- Functional package management for GNU
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;;; Copyright © 2018 Ricardo Wurmus <rekado@elephly.net>
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;;;
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;;; This file is part of GNU Guix.
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;;;
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;;; GNU Guix is free software; you can redistribute it and/or modify it
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;;; under the terms of the GNU General Public License as published by
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;;; the Free Software Foundation; either version 3 of the License, or (at
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;;; your option) any later version.
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;;;
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;;; GNU Guix is distributed in the hope that it will be useful, but
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;;; WITHOUT ANY WARRANTY; without even the implied warranty of
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;;; MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the
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;;; GNU General Public License for more details.
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;;;
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;;; You should have received a copy of the GNU General Public License
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;;; along with GNU Guix. If not, see <http://www.gnu.org/licenses/>.
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;; This is a specification for SELinux 2.7 written in the SELinux Common
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;; Intermediate Language (CIL). It refers to types that must be defined in
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;; the system's base policy.
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(block guix_daemon
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;; Require existing types
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(typeattributeset cil_gen_require init_t)
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(typeattributeset cil_gen_require tmp_t)
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(typeattributeset cil_gen_require nscd_var_run_t)
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(typeattributeset cil_gen_require var_log_t)
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(typeattributeset cil_gen_require domain)
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;; Declare own types
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(type guix_daemon_t)
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(roletype object_r guix_daemon_t)
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(type guix_daemon_conf_t)
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(roletype object_r guix_daemon_conf_t)
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(type guix_daemon_exec_t)
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(roletype object_r guix_daemon_exec_t)
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(type guix_daemon_socket_t)
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(roletype object_r guix_daemon_socket_t)
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(type guix_store_content_t)
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(roletype object_r guix_store_content_t)
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(type guix_profiles_t)
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(roletype object_r guix_profiles_t)
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;; These types are domains, thereby allowing process rules
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(typeattributeset domain (guix_daemon_t guix_daemon_exec_t))
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(level low (s0))
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;; When a process in init_t or guix_store_content_t spawns a
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;; guix_daemon_exec_t process, let it run in the guix_daemon_t context
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(typetransition init_t guix_daemon_exec_t
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process guix_daemon_t)
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(typetransition guix_store_content_t guix_daemon_exec_t
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process guix_daemon_t)
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;; Permit communication with NSCD
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(allow guix_daemon_t
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nscd_var_run_t
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(file (map read)))
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(allow guix_daemon_t
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nscd_var_run_t
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(dir (search)))
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(allow guix_daemon_t
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nscd_var_run_t
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(sock_file (write)))
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(allow guix_daemon_t
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nscd_t
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(fd (use)))
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(allow guix_daemon_t
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nscd_t
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(unix_stream_socket (connectto)))
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;; Permit logging and temp file access
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(allow guix_daemon_t
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tmp_t
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(lnk_file (setattr unlink)))
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(allow guix_daemon_t
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tmp_t
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(dir (create
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rmdir
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add_name remove_name
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open read write
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getattr setattr
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search)))
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(allow guix_daemon_t
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var_log_t
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(file (create getattr open write)))
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(allow guix_daemon_t
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var_log_t
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(dir (getattr write add_name)))
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(allow guix_daemon_t
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var_run_t
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(lnk_file (read)))
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(allow guix_daemon_t
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var_run_t
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(dir (search)))
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;; Spawning processes, execute helpers
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(allow guix_daemon_t
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self
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(process (fork)))
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(allow guix_daemon_t
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guix_daemon_exec_t
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(file (execute execute_no_trans read open)))
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;; TODO: unknown
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(allow guix_daemon_t
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root_t
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(dir (mounton)))
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(allow guix_daemon_t
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fs_t
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(filesystem (getattr)))
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(allow guix_daemon_conf_t
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fs_t
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(filesystem (associate)))
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;; Build isolation
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(allow guix_daemon_t
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guix_store_content_t
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(file (mounton)))
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(allow guix_store_content_t
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fs_t
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(filesystem (associate)))
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(allow guix_daemon_t
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guix_store_content_t
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(dir (mounton)))
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(allow guix_daemon_t
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guix_daemon_t
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(capability (net_admin
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fsetid fowner
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chown setuid setgid
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dac_override dac_read_search
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sys_chroot)))
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(allow guix_daemon_t
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fs_t
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(filesystem (unmount)))
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(allow guix_daemon_t
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devpts_t
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(filesystem (mount)))
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(allow guix_daemon_t
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devpts_t
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(chr_file (setattr getattr)))
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(allow guix_daemon_t
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tmpfs_t
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(filesystem (mount)))
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(allow guix_daemon_t
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tmpfs_t
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(dir (getattr)))
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(allow guix_daemon_t
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proc_t
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(filesystem (mount)))
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(allow guix_daemon_t
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null_device_t
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(chr_file (getattr open read write)))
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(allow guix_daemon_t
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kvm_device_t
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(chr_file (getattr)))
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(allow guix_daemon_t
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zero_device_t
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(chr_file (getattr)))
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(allow guix_daemon_t
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urandom_device_t
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(chr_file (getattr)))
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(allow guix_daemon_t
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random_device_t
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(chr_file (getattr)))
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(allow guix_daemon_t
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devtty_t
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(chr_file (getattr)))
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;; Access to store items
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(allow guix_daemon_t
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guix_store_content_t
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(dir (reparent
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create
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getattr setattr
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search rename
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add_name remove_name
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open write
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rmdir)))
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(allow guix_daemon_t
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guix_store_content_t
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(file (create
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lock
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setattr getattr
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execute execute_no_trans
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link unlink
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map
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rename
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open read write)))
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(allow guix_daemon_t
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guix_store_content_t
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(lnk_file (create
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getattr setattr
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link unlink
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read
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rename)))
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;; Access to configuration files and directories
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(allow guix_daemon_t
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guix_daemon_conf_t
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(dir (search
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setattr getattr
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add_name remove_name
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open read write)))
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(allow guix_daemon_t
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guix_daemon_conf_t
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(file (create
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lock
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map
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getattr setattr
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unlink
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open read write)))
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(allow guix_daemon_t
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guix_daemon_conf_t
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(lnk_file (create getattr rename unlink)))
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;; Access to profiles
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(allow guix_daemon_t
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guix_profiles_t
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(dir (getattr setattr read open)))
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(allow guix_daemon_t
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guix_profiles_t
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(lnk_file (read getattr)))
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;; Access to profile links in the home directory
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;; TODO: allow access to profile links *anywhere* on the filesystem
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(allow guix_daemon_t
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user_home_t
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(lnk_file (read getattr)))
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(allow guix_daemon_t
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user_home_t
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(dir (search)))
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;; Socket operations
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(allow guix_daemon_t
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init_t
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(fd (use)))
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(allow guix_daemon_t
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init_t
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(unix_stream_socket (write)))
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(allow guix_daemon_t
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guix_daemon_conf_t
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(unix_stream_socket (listen)))
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(allow guix_daemon_t
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guix_daemon_conf_t
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(sock_file (create unlink)))
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(allow guix_daemon_t
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self
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(unix_stream_socket (create
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read write
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connect bind accept
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getopt setopt)))
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(allow guix_daemon_t
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self
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(fifo_file (write read)))
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(allow guix_daemon_t
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self
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(udp_socket (ioctl create)))
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;; Label file system
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(filecon "@guix_sysconfdir@/guix(/.*)?"
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any (system_u object_r guix_daemon_conf_t (low low)))
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(filecon "@guix_localstatedir@/guix(/.*)?"
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any (system_u object_r guix_daemon_conf_t (low low)))
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(filecon "@guix_localstatedir@/guix/profiles(/.*)?"
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any (system_u object_r guix_profiles_t (low low)))
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(filecon "/gnu"
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dir (unconfined_u object_r guix_store_content_t (low low)))
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(filecon "@storedir@(/.+)?"
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any (unconfined_u object_r guix_store_content_t (low low)))
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(filecon "@storedir@/[^/]+/.+"
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any (unconfined_u object_r guix_store_content_t (low low)))
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(filecon "@prefix@/bin/guix-daemon"
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file (system_u object_r guix_daemon_exec_t (low low)))
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(filecon "@storedir@/.+-(guix-.+|profile)/bin/guix-daemon"
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file (system_u object_r guix_daemon_exec_t (low low)))
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(filecon "@storedir@/.+-(guix-.+|profile)/libexec/guix-authenticate"
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file (system_u object_r guix_daemon_exec_t (low low)))
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(filecon "@storedir@/.+-(guix-.+|profile)/libexec/guix/(.*)?"
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any (system_u object_r guix_daemon_exec_t (low low)))
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(filecon "@guix_localstatedir@/guix/daemon-socket/socket"
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any (system_u object_r guix_daemon_socket_t (low low))))
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