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Diffstat (limited to 'gnu/build/linux-container.scm')
| -rw-r--r-- | gnu/build/linux-container.scm | 260 |
1 files changed, 260 insertions, 0 deletions
diff --git a/gnu/build/linux-container.scm b/gnu/build/linux-container.scm new file mode 100644 index 0000000000..7a03a29d2c --- /dev/null +++ b/gnu/build/linux-container.scm @@ -0,0 +1,260 @@ +;;; 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) + "Configure the user namespace for PID." + (define proc-dir + (string-append "/proc/" (number->string pid))) + + (define (scope file) + (string-append proc-dir file)) + + ;; Only root can map more than a single uid/gid. A range of 65536 uid/gids + ;; is used to cover 16 bits worth of users and groups, which is sufficient + ;; for most cases. + ;; + ;; See also: http://www.freedesktop.org/software/systemd/man/systemd-nspawn.html#--private-users= + (let* ((uid (getuid)) + (gid (getgid)) + (uid-range (if (zero? uid) 65536 1)) + (gid-range (if (zero? gid) 65536 1))) + + ;; 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 uid-range))) + (call-with-output-file (scope "/gid_map") + (lambda (port) + (format port "0 ~d ~d" gid gid-range))))) + +(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 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." + ;; 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)) + ;; TODO: Initialize cgroups. + (close in) + (write 'ready out) + (close out) + pid)))))) + +(define* (call-with-container mounts thunk #:key (namespaces %namespaces)) + "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. + +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 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)))))) |