831bc1468e
It's not always possible to map 65536 uids when creating a container as the
root user within another user namespace. This is true when building Guix
within the build daemon's container. By using a uid range of 1 by default,
even as the root user, the tests now pass.
* gnu/build/linux-container.scm (initialize-user-namespace, run-container):
Add 'host-uids' argument.
(call-with-container): Add #:host-uids keyword argument.
* tests/containers.scm ("container-excursion"): Update 'run-container' call.
260 lines
9.9 KiB
Scheme
260 lines
9.9 KiB
Scheme
;;; GNU Guix --- Functional package management for GNU
|
|
;;; Copyright © 2015 David Thompson <davet@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 linux-container)
|
|
#:use-module (ice-9 format)
|
|
#:use-module (ice-9 match)
|
|
#:use-module (srfi srfi-98)
|
|
#:use-module (guix utils)
|
|
#:use-module (guix build utils)
|
|
#:use-module (guix build syscalls)
|
|
#:use-module ((gnu build file-systems) #:select (mount-file-system))
|
|
#:export (%namespaces
|
|
run-container
|
|
call-with-container
|
|
container-excursion))
|
|
|
|
(define %namespaces
|
|
'(mnt pid ipc uts user net))
|
|
|
|
(define (call-with-clean-exit thunk)
|
|
"Apply THUNK, but exit with a status code of 1 if it fails."
|
|
(dynamic-wind
|
|
(const #t)
|
|
thunk
|
|
(lambda ()
|
|
(primitive-exit 1))))
|
|
|
|
(define (purify-environment)
|
|
"Unset all environment variables."
|
|
(for-each unsetenv
|
|
(match (get-environment-variables)
|
|
(((names . _) ...) names))))
|
|
|
|
;; The container setup procedure closely resembles that of the Docker
|
|
;; specification:
|
|
;; https://raw.githubusercontent.com/docker/libcontainer/master/SPEC.md
|
|
(define* (mount-file-systems root mounts #:key mount-/sys? mount-/proc?)
|
|
"Mount the essential file systems and the those in the MOUNTS list relative
|
|
to ROOT, then make ROOT the new root directory for the process."
|
|
(define (scope dir)
|
|
(string-append root dir))
|
|
|
|
(define (bind-mount src dest)
|
|
(mount src dest "none" MS_BIND))
|
|
|
|
;; Like mount, but creates the mount point if it doesn't exist.
|
|
(define* (mount* source target type #:optional (flags 0) options
|
|
#:key (update-mtab? #f))
|
|
(mkdir-p target)
|
|
(mount source target type flags options #:update-mtab? update-mtab?))
|
|
|
|
;; The container's file system is completely ephemeral, sans directories
|
|
;; bind-mounted from the host.
|
|
(mount "none" root "tmpfs")
|
|
|
|
;; A proc mount requires a new pid namespace.
|
|
(when mount-/proc?
|
|
(mount* "none" (scope "/proc") "proc"
|
|
(logior MS_NOEXEC MS_NOSUID MS_NODEV)))
|
|
|
|
;; A sysfs mount requires the user to have the CAP_SYS_ADMIN capability in
|
|
;; the current network namespace.
|
|
(when mount-/sys?
|
|
(mount* "none" (scope "/sys") "sysfs"
|
|
(logior MS_NOEXEC MS_NOSUID MS_NODEV MS_RDONLY)))
|
|
|
|
(mount* "none" (scope "/dev") "tmpfs"
|
|
(logior MS_NOEXEC MS_STRICTATIME)
|
|
"mode=755")
|
|
|
|
;; Create essential device nodes via bind-mounting them from the
|
|
;; host, because a process within a user namespace cannot create
|
|
;; device nodes.
|
|
(for-each (lambda (device)
|
|
(when (file-exists? device)
|
|
;; Create the mount point file.
|
|
(call-with-output-file (scope device)
|
|
(const #t))
|
|
(bind-mount device (scope device))))
|
|
'("/dev/null"
|
|
"/dev/zero"
|
|
"/dev/full"
|
|
"/dev/random"
|
|
"/dev/urandom"
|
|
"/dev/tty"
|
|
"/dev/ptmx"
|
|
"/dev/fuse"))
|
|
|
|
;; Setup standard input/output/error.
|
|
(symlink "/proc/self/fd" (scope "/dev/fd"))
|
|
(symlink "/proc/self/fd/0" (scope "/dev/stdin"))
|
|
(symlink "/proc/self/fd/1" (scope "/dev/stdout"))
|
|
(symlink "/proc/self/fd/2" (scope "/dev/stderr"))
|
|
|
|
;; Mount user-specified file systems.
|
|
(for-each (lambda (spec)
|
|
(mount-file-system spec #:root root))
|
|
mounts)
|
|
|
|
;; Jail the process inside the container's root file system.
|
|
(let ((put-old (string-append root "/real-root")))
|
|
(mkdir put-old)
|
|
(pivot-root root put-old)
|
|
(chdir "/")
|
|
(umount "real-root" MNT_DETACH)
|
|
(rmdir "real-root")))
|
|
|
|
(define (initialize-user-namespace pid host-uids)
|
|
"Configure the user namespace for PID. HOST-UIDS specifies the number of
|
|
host user identifiers to map into the user namespace."
|
|
(define proc-dir
|
|
(string-append "/proc/" (number->string pid)))
|
|
|
|
(define (scope file)
|
|
(string-append proc-dir file))
|
|
|
|
(let ((uid (getuid))
|
|
(gid (getgid)))
|
|
|
|
;; Only root can write to the gid map without first disabling the
|
|
;; setgroups syscall.
|
|
(unless (and (zero? uid) (zero? gid))
|
|
(call-with-output-file (scope "/setgroups")
|
|
(lambda (port)
|
|
(display "deny" port))))
|
|
|
|
;; Map the user/group that created the container to the root user
|
|
;; within the container.
|
|
(call-with-output-file (scope "/uid_map")
|
|
(lambda (port)
|
|
(format port "0 ~d ~d" uid host-uids)))
|
|
(call-with-output-file (scope "/gid_map")
|
|
(lambda (port)
|
|
(format port "0 ~d ~d" gid host-uids)))))
|
|
|
|
(define (namespaces->bit-mask namespaces)
|
|
"Return the number suitable for the 'flags' argument of 'clone' that
|
|
corresponds to the symbols in NAMESPACES."
|
|
(apply logior SIGCHLD
|
|
(map (match-lambda
|
|
('mnt CLONE_NEWNS)
|
|
('uts CLONE_NEWUTS)
|
|
('ipc CLONE_NEWIPC)
|
|
('user CLONE_NEWUSER)
|
|
('pid CLONE_NEWPID)
|
|
('net CLONE_NEWNET))
|
|
namespaces)))
|
|
|
|
(define (run-container root mounts namespaces host-uids thunk)
|
|
"Run THUNK in a new container process and return its PID. ROOT specifies
|
|
the root directory for the container. MOUNTS is a list of file system specs
|
|
that specify the mapping of host file systems into the container. NAMESPACES
|
|
is a list of symbols that correspond to the possible Linux namespaces: mnt,
|
|
ipc, uts, user, and net. HOST-UIDS specifies the number of
|
|
host user identifiers to map into the user namespace."
|
|
;; The parent process must initialize the user namespace for the child
|
|
;; before it can boot. To negotiate this, a pipe is used such that the
|
|
;; child process blocks until the parent writes to it.
|
|
(match (pipe)
|
|
((in . out)
|
|
(let ((flags (namespaces->bit-mask namespaces)))
|
|
(match (clone flags)
|
|
(0
|
|
(call-with-clean-exit
|
|
(lambda ()
|
|
(close out)
|
|
;; Wait for parent to set things up.
|
|
(read in)
|
|
(close in)
|
|
(purify-environment)
|
|
(when (memq 'mnt namespaces)
|
|
(mount-file-systems root mounts
|
|
#:mount-/proc? (memq 'pid namespaces)
|
|
#:mount-/sys? (memq 'net namespaces)))
|
|
;; TODO: Manage capabilities.
|
|
(thunk))))
|
|
(pid
|
|
(when (memq 'user namespaces)
|
|
(initialize-user-namespace pid host-uids))
|
|
;; TODO: Initialize cgroups.
|
|
(close in)
|
|
(write 'ready out)
|
|
(close out)
|
|
pid))))))
|
|
|
|
(define* (call-with-container mounts thunk #:key (namespaces %namespaces)
|
|
(host-uids 1))
|
|
"Run THUNK in a new container process and return its exit status.
|
|
MOUNTS is a list of file system specs that specify the mapping of host file
|
|
systems into the container. NAMESPACES is a list of symbols corresponding to
|
|
the identifiers for Linux namespaces: mnt, ipc, uts, pid, user, and net. By
|
|
default, all namespaces are used. HOST-UIDS is the number of host user
|
|
identifiers to map into the container's user namespace, if there is one. By
|
|
default, only a single uid/gid, that of the current user, is mapped into the
|
|
container. The host user that creates the container is the root user (uid/gid
|
|
0) within the container. Only root can map more than a single uid/gid.
|
|
|
|
Note that if THUNK needs to load any additional Guile modules, the relevant
|
|
module files must be present in one of the mappings in MOUNTS and the Guile
|
|
load path must be adjusted as needed."
|
|
(call-with-temporary-directory
|
|
(lambda (root)
|
|
(let ((pid (run-container root mounts namespaces host-uids thunk)))
|
|
;; Catch SIGINT and kill the container process.
|
|
(sigaction SIGINT
|
|
(lambda (signum)
|
|
(false-if-exception
|
|
(kill pid SIGKILL))))
|
|
|
|
(match (waitpid pid)
|
|
((_ . status) status))))))
|
|
|
|
(define (container-excursion pid thunk)
|
|
"Run THUNK as a child process within the namespaces of process PID and
|
|
return the exit status."
|
|
(define (namespace-file pid namespace)
|
|
(string-append "/proc/" (number->string pid) "/ns/" namespace))
|
|
|
|
(match (primitive-fork)
|
|
(0
|
|
(call-with-clean-exit
|
|
(lambda ()
|
|
(for-each (lambda (ns)
|
|
(call-with-input-file (namespace-file (getpid) ns)
|
|
(lambda (current-ns-port)
|
|
(call-with-input-file (namespace-file pid ns)
|
|
(lambda (new-ns-port)
|
|
;; Joining the namespace that the process
|
|
;; already belongs to would throw an error.
|
|
(unless (= (port->fdes current-ns-port)
|
|
(port->fdes new-ns-port))
|
|
(setns (port->fdes new-ns-port) 0)))))))
|
|
;; It's important that the user namespace is joined first,
|
|
;; so that the user will have the privileges to join the
|
|
;; other namespaces. Furthermore, it's important that the
|
|
;; mount namespace is joined last, otherwise the /proc mount
|
|
;; point would no longer be accessible.
|
|
'("user" "ipc" "uts" "net" "pid" "mnt"))
|
|
(purify-environment)
|
|
(chdir "/")
|
|
(thunk))))
|
|
(pid
|
|
(match (waitpid pid)
|
|
((_ . status)
|
|
(status:exit-val status))))))
|