util-linux: Add PACKAGECONFIG option to mitigate rootfs remount error

The 2.39 version of util-linux took new file descriptors based mount
kernel API into use. In relation to this change, the upstream release
notes in
https://github.com/util-linux/util-linux/blob/v2.39/Documentation/releases/v2.39-ReleaseNotes#L14-L21
mention that

  This change is very aggressive to libmount code, but hopefully, it does not introduce regressions in traditional mount(8) behavior.

After observing following failure when booting a board using a bit
older 6.1 series kernel together with initramfs rootfs based boot flow

  [FAILED] Failed to start Remount Root and Kernel File Systems.
  See 'systemctl status systemd-remount-fs.service' for details.

closer inspection revealed:

  demoboard ~ # systemctl status -l systemd-remount-fs.service
  x systemd-remount-fs.service - Remount Root and Kernel File Systems
       Loaded: loaded (/usr/lib/systemd/system/systemd-remount-fs.service; enabled-runtime; preset: disabled)
       Active: failed (Result: exit-code) since Wed 2024-08-14 14:53:48 UTC; 1min 22s ago
         Docs: man:systemd-remount-fs.service(8)
               https://www.freedesktop.org/wiki/Software/systemd/APIFileSystems
      Process: 76 ExecStart=/usr/lib/systemd/systemd-remount-fs (code=exited, status=1/FAILURE)
     Main PID: 76 (code=exited, status=1/FAILURE)

  Aug 14 14:53:48 demoboard systemd-remount-fs[76]: /usr/bin/mount for / exited with exit status 32.
  Aug 14 14:53:48 demoboard systemd-remount-fs[81]: mount: /: mount point not mounted or bad option.
  Aug 14 14:53:48 demoboard systemd-remount-fs[81]:        dmesg(1) may have more information after failed mount system call.
  Aug 14 14:53:48 demoboard systemd[1]: systemd-remount-fs.service: Main process exited, code=exited, status=1/FAILURE
  Aug 14 14:53:48 demoboard systemd[1]: systemd-remount-fs.service: Failed with result 'exit-code'.
  Aug 14 14:53:48 demoboard systemd[1]: Failed to start Remount Root and Kernel File Systems.

also consequentially, 'systemctl status' reported:

  State: degraded

When issuing 'strace -ff mount -o remount /' the failure occurred at

  mount_setattr(3, "", AT_EMPTY_PATH, {attr_set=MOUNT_ATTR_RDONLY|MOUNT_ATTR_NOATIME|MOUNT_ATTR_NODIRATIME, attr_clr=MOUNT_ATTR_NOSUID|MOUNT_ATTR_NODEV|MOUNT_ATTR_NOEXEC|MOUNT_ATTR_NOATIME|MOUNT_ATTR_STRICTATIME|MOUNT_ATTR_NOSYMFOLLOW|0x40, propagation=0 /* MS_??? */, userns_fd=0}, 32) = -1 EINVAL (Invalid argument)

After further investigation, The issue was pinpointed to lack of Linux
kernel commit
https://git.kernel.org/pub/scm/linux/kernel/git/stable/linux.git/commit/?id=95de4ad173ca0e61034f3145d66917970961c210
("fs: relax mount_setattr() permission checks") in the kernel version
that was being used. Above mitigation was discussed in email related to
then-rejected CVE-2024-26821:
https://lore.kernel.org/linux-cve-announce/2024051606-imaging-entrench-b327@gregkh/T/

After testing with qemuarm64 machine different linux-yocto versions,
it was observed that the issue impacts following versions of currently
supported LTS kernels:
 - 6.6.17 (fixed since 6.6.18 i.e. mount_setattr() returns 0)
 - 6.1.78 (fixed since 6.1.79 i.e. mount_setattr() returns 0)
 - 5.15.164 which is currently the newest of 5.15.y series (i.e. no
   known working version)

Taking the above findings into consideration, add a new PACKAGECONFIG
option removing which enables users to opt-out from using the feature
which can cause issues with a bit older kernels. The option is enabled
only for class-target here, since it otherwise causes following error
during util-linux-native's do_configure task on Debian 11 build host
(mountfd_api requirement fails):

   | configure: error: libmount_mountfd_support selected, but required mount FDs based API not available

Versions 5.10.223, 5.4.279 and 4.10.317 were also tested with qemuarm64
but the issue was not reproduced with those versions - using strace
showed that the mount_setattr call associated with the new mount API
problem was not issued with these LTS kernel versions, which seemed to
be confirmed also by following libmount debug message in these cases:

  415: libmount:     HOOK: [0x7fa115e818]: failed to init new API

Note: In addition to the aforementioned, this change was tested also
briefly using the current latest kernel versions 6.1.104, 6.6.45 and
6.10.3 that using the old mount API with newest kernels did not
introduce any observable regression to the boot flow.

(From OE-Core rev: dc086d9a8613143607af3583c72ed892e20b4d66)

Signed-off-by: Niko Mauno <niko.mauno@vaisala.com>
Signed-off-by: Richard Purdie <richard.purdie@linuxfoundation.org>

0 files changed, 0 insertions, 0 deletions