civodul pushed a commit to branch master
in repository guix.
commit a57ed987ffd1452ba5a4d70feb54893e99b8e076
Author: Ludovic Courtès <l...@gnu.org>
AuthorDate: Tue Apr 8 14:03:48 2025 +0200
linux-container: Lock mounts by default.
This makes it impossible to unmount or remount things from within
‘call-with-container’.
* gnu/build/linux-container.scm (initialize-user-namespace):
Add #:host-uid and #:host-gid. and honor them.
(run-container): Add #:lock-mounts?. Honor it by calling ‘unshare’
followed by ‘initialize-user-namespace’.
(call-with-container): Add #:lock-mounts? and pass it down.
(container-excursion): Get the user namespace owning the PID namespace
and join it, then join the remaining namespaces.
* tests/containers.scm ("call-with-container, mnt namespace, locked
mounts"):
New test.
("container-excursion"): Pass #:lock-mounts? #f.
Change-Id: I13be982aef99e68a653d472f0e595c81cfcfa392
---
gnu/build/linux-container.scm | 111 ++++++++++++++++++++++++++++--------------
tests/containers.scm | 33 +++++++++++--
2 files changed, 103 insertions(+), 41 deletions(-)
diff --git a/gnu/build/linux-container.scm b/gnu/build/linux-container.scm
index 345ce2de08..51f04bc249 100644
--- a/gnu/build/linux-container.scm
+++ b/gnu/build/linux-container.scm
@@ -189,7 +189,10 @@ for the process."
(remount-read-only "/"))))
(define* (initialize-user-namespace pid host-uids
- #:key (guest-uid 0) (guest-gid 0))
+ #:key
+ (host-uid (getuid))
+ (host-gid (getgid))
+ (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)
@@ -200,24 +203,21 @@ map to in the namespace."
(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")
+ ;; Only root can write to the gid map without first disabling the
+ ;; setgroups syscall.
+ (unless (and (zero? host-uid) (zero? host-gid))
+ (call-with-output-file (scope "/setgroups")
(lambda (port)
- (format port "~d ~d ~d" guest-gid gid host-uids)))))
+ (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 host-uid host-uids)))
+ (call-with-output-file (scope "/gid_map")
+ (lambda (port)
+ (format port "~d ~d ~d" guest-gid host-gid host-uids))))
(define (namespaces->bit-mask namespaces)
"Return the number suitable for the 'flags' argument of 'clone' that
@@ -238,12 +238,14 @@ corresponds to the symbols in NAMESPACES."
#:key (guest-uid 0) (guest-gid 0)
(populate-file-system (const #t))
(loopback-network? #t)
+ (lock-mounts? #t)
writable-root?)
"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.
+ipc, uts, user, and net. When LOCK-MOUNTS? is true, arrange so that none of
+MOUNTS can be unmounted or remounted individually from within THUNK.
When LOOPBACK-NETWORK? is true and 'net is amount NAMESPACES, set up the
loopback device (\"lo\") and a minimal /etc/hosts.
@@ -303,6 +305,28 @@ that host UIDs (respectively GIDs) map to in the
namespace."
;; cannot be 'read' so they shouldn't be written as is.
(write args child)
(primitive-exit 3))))
+
+ (when (and lock-mounts?
+ (memq 'mnt namespaces)
+ (memq 'user namespaces))
+ ;; Create a new mount namespace owned by a new user
+ ;; namespace to "lock" together previous mounts, such that
+ ;; they cannot be unmounted or remounted separately--see
+ ;; mount_namespaces(7).
+ ;;
+ ;; Note: at this point, the process is single-threaded (no
+ ;; GC mark threads, no finalization thread, etc.) which is
+ ;; why unshare(CLONE_NEWUSER) can be used.
+ (let ((uid (getuid)) (gid (getgid)))
+ (unshare (logior CLONE_NEWUSER CLONE_NEWNS))
+ (when (file-exists? "/proc/self")
+ (initialize-user-namespace (getpid)
+ host-uids
+ #:host-uid uid
+ #:host-gid gid
+ #:guest-uid guest-uid
+ #:guest-gid guest-gid))))
+
;; TODO: Manage capabilities.
(write 'ready child)
(close-port child)
@@ -365,6 +389,7 @@ if there are no child processes left."
(define* (call-with-container mounts thunk #:key (namespaces %namespaces)
(host-uids 1) (guest-uid 0) (guest-gid 0)
+ (lock-mounts? #t)
(relayed-signals (list SIGINT SIGTERM))
(child-is-pid1? #t)
(populate-file-system (const #t))
@@ -449,6 +474,7 @@ load path must be adjusted as needed."
(call-with-temporary-directory
(lambda (root)
(let ((pid (run-container root mounts namespaces host-uids thunk*
+ #:lock-mounts? lock-mounts?
#:guest-uid guest-uid
#:guest-gid guest-gid
#:populate-file-system populate-file-system
@@ -469,24 +495,35 @@ return the exit status, an integer as returned by
'waitpid'."
(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"))
+ ;; First, determine the user namespace that owns the pid namespace and
+ ;; join that user namespace (the assumption is that it also owns all
+ ;; the other namespaces). It's important that the user namespace is
+ ;; joined first, so that the user will have the privileges to join the
+ ;; other namespaces.
+ (let* ((pid-ns (open-fdes (namespace-file pid "pid")
+ (logior O_CLOEXEC O_RDONLY)))
+ (user-ns (get-user-ns pid-ns)))
+ (close-fdes pid-ns)
+ (unless (equal? (stat user-ns)
+ (stat (namespace-file (getpid) "user")))
+ (setns user-ns 0))
+ (close-fdes user-ns)
+
+ ;; Then join all the remaining namespaces.
+ (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 target
+ (lambda (new-ns-port)
+ (setns (fileno new-ns-port) 0))))))
+ ;; It's important that the mount namespace is joined last,
+ ;; otherwise the /proc mount point would no longer be
+ ;; accessible.
+ '("ipc" "uts" "net" "pid" "mnt")))
(purify-environment)
(chdir "/")
diff --git a/tests/containers.scm b/tests/containers.scm
index 1e915d517e..6edea9631d 100644
--- a/tests/containers.scm
+++ b/tests/containers.scm
@@ -1,6 +1,6 @@
;;; GNU Guix --- Functional package management for GNU
;;; Copyright © 2015 David Thompson <da...@gnu.org>
-;;; Copyright © 2016, 2017, 2019, 2023 Ludovic Courtès <l...@gnu.org>
+;;; Copyright © 2016-2017, 2019, 2023, 2025 Ludovic Courtès <l...@gnu.org>
;;;
;;; This file is part of GNU Guix.
;;;
@@ -110,6 +110,26 @@
(assert-exit (file-exists? "/testing")))
#:namespaces '(user mnt))))
+(skip-if-unsupported)
+(test-equal "call-with-container, mnt namespace, locked mounts"
+ EINVAL
+ ;; umount(2) fails with EINVAL when targeting a mount point that is
+ ;; "locked".
+ (status:exit-val
+ (call-with-container (list (file-system
+ (device "none")
+ (mount-point "/testing")
+ (type "tmpfs")
+ (check? #f)))
+ (lambda ()
+ (primitive-exit (catch 'system-error
+ (lambda ()
+ (umount "/testing")
+ 0)
+ (lambda args
+ (system-error-errno args)))))
+ #:namespaces '(user mnt))))
+
(skip-if-unsupported)
(test-equal "call-with-container, mnt namespace, wrong bind mount"
`(system-error ,ENOENT)
@@ -169,7 +189,8 @@
#:namespaces '(user mnt))))
(skip-if-unsupported)
-(test-assert "container-excursion"
+(test-equal "container-excursion"
+ 0
(call-with-temporary-directory
(lambda (root)
;; Two pipes: One for the container to signal that the test can begin,
@@ -193,7 +214,11 @@
(readlink (string-append "/proc/" pid "/ns/" ns)))
'("user" "ipc" "uts" "net" "pid" "mnt"))))
- (let* ((pid (run-container root '() %namespaces 1 container))
+ (let* ((pid (run-container root '() %namespaces 1 container
+ ;; Do not lock mounts so the user namespace
+ ;; appears to be the same seen from inside
+ ;; and from outside.
+ #:lock-mounts? #f))
(container-namespaces (namespaces pid))
(result
(begin
@@ -213,7 +238,7 @@
(write 'done end-out)
(close end-out)
(waitpid pid)
- (zero? result)))))))
+ result))))))
(skip-if-unsupported)
(test-equal "container-excursion, same namespaces"
