0ef8fe22ed
Fixes <https://issues.guix.gnu.org/61156>. * gnu/build/linux-container.scm (container-excursion): Add extra call to 'primitive-fork' and invoke THUNK in the child process. * tests/containers.scm ("container-excursion"): Remove extra 'primitive-fork' call, now unnecessary. ("container-excursion*, /proc"): New test.
471 lines
19 KiB
Scheme
471 lines
19 KiB
Scheme
;;; GNU Guix --- Functional package management for GNU
|
|
;;; Copyright © 2015 David Thompson <davet@gnu.org>
|
|
;;; Copyright © 2017-2019, 2022, 2023 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 linux-container)
|
|
#:use-module (ice-9 format)
|
|
#:use-module (ice-9 match)
|
|
#:use-module (ice-9 rdelim)
|
|
#:use-module (srfi srfi-98)
|
|
#:use-module (guix build utils)
|
|
#:use-module (guix build syscalls)
|
|
#:use-module (gnu system file-systems) ;<file-system>
|
|
#:use-module ((gnu build file-systems) #:select (mount-file-system))
|
|
#:export (user-namespace-supported?
|
|
unprivileged-user-namespace-supported?
|
|
setgroups-supported?
|
|
%namespaces
|
|
run-container
|
|
call-with-container
|
|
container-excursion
|
|
container-excursion*))
|
|
|
|
(define (user-namespace-supported?)
|
|
"Return #t if user namespaces are supported on this system."
|
|
(file-exists? "/proc/self/ns/user"))
|
|
|
|
(define (unprivileged-user-namespace-supported?)
|
|
"Return #t if user namespaces can be created by unprivileged users."
|
|
(let ((userns-file "/proc/sys/kernel/unprivileged_userns_clone"))
|
|
(if (file-exists? userns-file)
|
|
(eqv? #\1 (call-with-input-file userns-file read-char))
|
|
#t)))
|
|
|
|
(define (setgroups-supported?)
|
|
"Return #t if the setgroups proc file, introduced in Linux-libre 3.19,
|
|
exists."
|
|
(file-exists? "/proc/self/setgroups"))
|
|
|
|
(define %namespaces
|
|
'(cgroup 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)
|
|
(lambda ()
|
|
(thunk)
|
|
|
|
;; XXX: Somehow we sometimes get EBADF from write(2) or close(2) upon
|
|
;; exit (coming from fd finalizers) when used by the Shepherd. To work
|
|
;; around that, exit forcefully so fd finalizers don't have a chance to
|
|
;; run and fail.
|
|
(primitive-_exit 0))
|
|
(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 MOUNTS, a list of
|
|
<file-system> objects, relative to ROOT; then make ROOT the new root directory
|
|
for the process."
|
|
(define (scope dir)
|
|
(string-append root dir))
|
|
|
|
(define (touch file-name)
|
|
(call-with-output-file file-name (const #t)))
|
|
|
|
(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.
|
|
(touch (scope device))
|
|
(bind-mount device (scope device))))
|
|
'("/dev/null"
|
|
"/dev/zero"
|
|
"/dev/full"
|
|
"/dev/random"
|
|
"/dev/urandom"
|
|
"/dev/tty"
|
|
"/dev/fuse"))
|
|
|
|
;; Mount a new devpts instance on /dev/pts.
|
|
(when (file-exists? "/dev/ptmx")
|
|
(mount* "none" (scope "/dev/pts") "devpts" 0
|
|
"newinstance,mode=0620")
|
|
(symlink "/dev/pts/ptmx" (scope "/dev/ptmx")))
|
|
|
|
;; Setup the container's /dev/console by bind mounting the pseudo-terminal
|
|
;; associated with standard input when there is one.
|
|
(let* ((in (current-input-port))
|
|
(tty (catch 'system-error
|
|
(lambda ()
|
|
;; This call throws if IN does not correspond to a tty.
|
|
;; This is more reliable than 'isatty?'.
|
|
(ttyname in))
|
|
(const #f)))
|
|
(console (scope "/dev/console")))
|
|
(when tty
|
|
(touch console)
|
|
(chmod console #o600)
|
|
(bind-mount tty console)))
|
|
|
|
;; 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 (file-system)
|
|
(mount-file-system file-system #: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")
|
|
(chmod "/" #o755)))
|
|
|
|
(define* (initialize-user-namespace pid host-uids
|
|
#:key (guest-uid 0) (guest-gid 0))
|
|
"Configure the user namespace for PID. HOST-UIDS specifies the number of
|
|
host user identifiers to map into the user namespace. GUEST-UID and GUEST-GID
|
|
specify the first UID (respectively GID) that host UIDs (respectively GIDs)
|
|
map to in the 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 "~d ~d ~d" guest-uid uid host-uids)))
|
|
(call-with-output-file (scope "/gid_map")
|
|
(lambda (port)
|
|
(format port "~d ~d ~d" guest-gid 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."
|
|
;; Use the same flags as fork(3) in addition to the namespace flags.
|
|
(apply logior SIGCHLD
|
|
(map (match-lambda
|
|
('cgroup CLONE_NEWCGROUP)
|
|
('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
|
|
#:key (guest-uid 0) (guest-gid 0))
|
|
"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>
|
|
objects that specify file systems to mount inside 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. GUEST-UID and GUEST-GID specify the first UID (respectively GID)
|
|
that host UIDs (respectively GIDs) map to in the 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 (socketpair PF_UNIX (logior SOCK_CLOEXEC SOCK_STREAM) 0)
|
|
((child . parent)
|
|
(let ((flags (namespaces->bit-mask namespaces)))
|
|
(match (clone flags)
|
|
(0
|
|
(call-with-clean-exit
|
|
(lambda ()
|
|
(close-port parent)
|
|
;; Wait for parent to set things up.
|
|
(match (read child)
|
|
('ready
|
|
(purify-environment)
|
|
(when (and (memq 'mnt namespaces)
|
|
(not (string=? root "/")))
|
|
(catch #t
|
|
(lambda ()
|
|
(mount-file-systems root mounts
|
|
#:mount-/proc? (memq 'pid namespaces)
|
|
#:mount-/sys? (memq 'net
|
|
namespaces)))
|
|
(lambda args
|
|
;; Forward the exception to the parent process.
|
|
;; FIXME: SRFI-35 conditions and non-trivial objects
|
|
;; cannot be 'read' so they shouldn't be written as is.
|
|
(write args child)
|
|
(primitive-exit 3))))
|
|
;; TODO: Manage capabilities.
|
|
(write 'ready child)
|
|
(close-port child)
|
|
(thunk))
|
|
(_ ;parent died or something
|
|
(primitive-exit 2))))))
|
|
(pid
|
|
(close-port child)
|
|
(when (memq 'user namespaces)
|
|
(initialize-user-namespace pid host-uids
|
|
#:guest-uid guest-uid
|
|
#:guest-gid guest-gid))
|
|
;; TODO: Initialize cgroups.
|
|
(write 'ready parent)
|
|
(newline parent)
|
|
|
|
;; Check whether the child process' setup phase succeeded.
|
|
(let ((message (read parent)))
|
|
(close-port parent)
|
|
(match message
|
|
('ready ;success
|
|
pid)
|
|
(((? symbol? key) args ...) ;exception
|
|
(apply throw key args))
|
|
(_ ;unexpected termination
|
|
#f)))))))))
|
|
|
|
;; FIXME: This is copied from (guix utils), which we cannot use because it
|
|
;; would pull (guix config) and all.
|
|
(define (call-with-temporary-directory proc)
|
|
"Call PROC with a name of a temporary directory; close the directory and
|
|
delete it when leaving the dynamic extent of this call."
|
|
(let* ((directory (or (getenv "TMPDIR") "/tmp"))
|
|
(template (string-append directory "/guix-directory.XXXXXX"))
|
|
(tmp-dir (mkdtemp! template)))
|
|
(dynamic-wind
|
|
(const #t)
|
|
(lambda ()
|
|
(proc tmp-dir))
|
|
(lambda ()
|
|
(false-if-exception (delete-file-recursively tmp-dir))))))
|
|
|
|
(define (wait-child-process)
|
|
"Wait for one child process and return a pair, like 'waitpid', or return #f
|
|
if there are no child processes left."
|
|
(catch 'system-error
|
|
(lambda ()
|
|
(waitpid WAIT_ANY))
|
|
(lambda args
|
|
(if (= ECHILD (system-error-errno args))
|
|
#f
|
|
(apply throw args)))))
|
|
|
|
(define (status->exit-status status)
|
|
"Reify STATUS as an exit status."
|
|
(or (status:exit-val status)
|
|
;; See <http://www.tldp.org/LDP/abs/html/exitcodes.html#EXITCODESREF>.
|
|
(+ 128 (or (status:term-sig status)
|
|
(status:stop-sig status)))))
|
|
|
|
(define* (call-with-container mounts thunk #:key (namespaces %namespaces)
|
|
(host-uids 1) (guest-uid 0) (guest-gid 0)
|
|
(relayed-signals (list SIGINT SIGTERM))
|
|
(child-is-pid1? #t)
|
|
(process-spawned-hook (const #t)))
|
|
"Run THUNK in a new container process and return its exit status; call
|
|
PROCESS-SPAWNED-HOOK with the PID of the new process that has been spawned.
|
|
MOUNTS is a list of <file-system> objects that specify file systems to mount
|
|
inside 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.
|
|
|
|
GUEST-UID and GUEST-GID specify the first UID (respectively GID) that host
|
|
UIDs (respectively GIDs) map to in the namespace.
|
|
|
|
RELAYED-SIGNALS is the list of signals that are \"relayed\" to the container
|
|
process when caught by its parent.
|
|
|
|
When CHILD-IS-PID1? is true, and if NAMESPACES contains 'pid', then the child
|
|
process runs directly as PID 1. As such, it is responsible for (1) installing
|
|
signal handlers and (2) reaping terminated processes by calling 'waitpid'.
|
|
When CHILD-IS-PID1? is false, a new intermediate process is created instead
|
|
that takes this responsibility.
|
|
|
|
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."
|
|
(define thunk*
|
|
(if (and (memq 'pid namespaces)
|
|
(not child-is-pid1?))
|
|
(lambda ()
|
|
;; Behave like an init process: create a sub-process that calls
|
|
;; THUNK, and wait for child processes. Furthermore, forward
|
|
;; RELAYED-SIGNALS to the child process.
|
|
(match (primitive-fork)
|
|
(0
|
|
(call-with-clean-exit thunk))
|
|
(pid
|
|
(install-signal-handlers pid)
|
|
(let loop ()
|
|
(match (wait-child-process)
|
|
((child . status)
|
|
(if (= child pid)
|
|
(primitive-exit (status->exit-status status))
|
|
(loop)))
|
|
(#f
|
|
(primitive-exit 128))))))) ;cannot happen
|
|
thunk))
|
|
|
|
(define (periodically-schedule-asyncs)
|
|
;; XXX: In Guile there's a time window where a signal-handling async could
|
|
;; be queued without being processed by the time we enter a blocking
|
|
;; syscall like waitpid(2) (info "(guile) Signals"). This terrible hack
|
|
;; ensures pending asyncs get a chance to run periodically.
|
|
(sigaction SIGALRM (lambda _ (alarm 1)))
|
|
(alarm 1))
|
|
|
|
(define (install-signal-handlers pid)
|
|
;; Install handlers that forward signals to PID.
|
|
(define (relay-signal signal)
|
|
(false-if-exception (kill pid signal)))
|
|
|
|
(periodically-schedule-asyncs)
|
|
(for-each (lambda (signal)
|
|
(sigaction signal relay-signal))
|
|
relayed-signals))
|
|
|
|
(call-with-temporary-directory
|
|
(lambda (root)
|
|
(let ((pid (run-container root mounts namespaces host-uids thunk*
|
|
#:guest-uid guest-uid
|
|
#:guest-gid guest-gid)))
|
|
(install-signal-handlers pid)
|
|
(process-spawned-hook pid)
|
|
(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, an integer as returned by 'waitpid'."
|
|
(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)
|
|
(let ((source (namespace-file (getpid) ns))
|
|
(target (namespace-file pid ns)))
|
|
;; Joining the namespace that the process already
|
|
;; belongs to would throw an error so avoid that.
|
|
;; XXX: This /proc interface leads to TOCTTOU.
|
|
(unless (string=? (readlink source) (readlink target))
|
|
(call-with-input-file source
|
|
(lambda (current-ns-port)
|
|
(call-with-input-file target
|
|
(lambda (new-ns-port)
|
|
(setns (fileno 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 "/")
|
|
|
|
;; Per setns(2), changing the PID namespace only applies to child
|
|
;; processes, not to the process itself. Thus fork so that THUNK runs
|
|
;; in the right PID namespace, which also gives it access to /proc.
|
|
(match (primitive-fork)
|
|
(0 (call-with-clean-exit thunk))
|
|
(pid (primitive-exit
|
|
(match (waitpid pid)
|
|
((_ . status)
|
|
(or (status:exit-val status) 127)))))))))
|
|
(pid
|
|
(match (waitpid pid)
|
|
((_ . status)
|
|
status)))))
|
|
|
|
(define (container-excursion* pid thunk)
|
|
"Like 'container-excursion', but return the return value of THUNK."
|
|
(match (pipe)
|
|
((in . out)
|
|
;; Make sure IN and OUT are not inherited if THUNK forks + execs.
|
|
(fcntl in F_SETFD FD_CLOEXEC)
|
|
(fcntl out F_SETFD FD_CLOEXEC)
|
|
|
|
(match (container-excursion pid
|
|
(lambda ()
|
|
(close-port in)
|
|
(write (thunk) out)
|
|
(close-port out)))
|
|
(0
|
|
(close-port out)
|
|
(let ((result (read in)))
|
|
(close-port in)
|
|
result))
|
|
(_ ;maybe PID died already
|
|
(close-port out)
|
|
(close-port in)
|
|
#f)))))
|