alpine: avoid wiping out writable host mounts under /home, etc.

A host directory could be wiped out when all the following conditions are met:
- The directory is mounted to Lima via virtiofs, or, potentially 9p
- The mount is writable
- The mount point in the guest is under one of: /etc /home /root /usr/local /var/lib
- The guest OS is Alpine Linux

Fix issue 2221
Fix rancher-sandbox/rancher-desktop issue 6582

Co-authored-by: Jan Dubois <[email protected]>
Signed-off-by: Akihiro Suda <[email protected]>

pkg/cidata/cidata.TEMPLATE.d/boot/04-persistent-data-volume.sh

@@ -61,21 +61,42 @@ if [ "$(awk '$2 == "/" {print $3}' /proc/mounts)" == "tmpfs" ]; then
  PART=$(lsblk --list /dev/"${DISK}" --noheadings --output name,type | awk '$2 == "part" {print $1}')
  mkfs.ext4 -L data-volume /dev/"${PART}"
  mount -t ext4 /dev/disk/by-label/data-volume /mnt/data
- # Unmount all mount points under /tmp so we can move it to the data volume:
- # "mount1 on /tmp/lima type 9p (rw,dirsync,relatime,mmap,access=client,trans=virtio)"
- for MP in $(mount | awk '$3 ~ /^\/tmp\// {print $3}'); do
- umount "${MP}"
- done
  # setup apk package cache
  mkdir -p /mnt/data/apk/cache
  mkdir -p /etc/apk
  ln -s /mnt/data/apk/cache /etc/apk/cache
+ # Prepare mnt.sh (used for restoring mounts later)
+ echo "#!/bin/sh" >/mnt/data/mnt.sh
+ echo "set -eux" >>/mnt/data/mnt.sh
  # Move all persisted directories to the data volume
  for DIR in ${DATADIRS}; do
  DEST="/mnt/data$(dirname "${DIR}")"
  mkdir -p "${DIR}" "${DEST}"
+ while IFS= read -r LINE; do
+ [ -z "$LINE" ] && continue
+ MNTDEV="$(echo "${LINE}" | awk '{print $1}')"
+ # unmangle " \t\n\\#"
+ # https://github.com/torvalds/linux/blob/v6.6/fs/proc_namespace.c#L89
+ MNTPNT="$(echo "${LINE}" | awk '{print $2}' | sed -e 's/\\040/ /g; s/\\011/\t/g; s/\\012/\n/g; s/\\134/\\/g; s/\\043/#/g')"
+ # Ignore if MNTPNT is neither DIR nor a parent directory of DIR.
+ # It is not a parent if MNTPNT doesn't start with DIR, or the first
+ # character after DIR isn't a slash.
+ # shellcheck disable=SC2295
+ WITHOUT_DIR=${MNTPNT#$DIR}
+ # shellcheck disable=SC2166
+ [ "$MNTPNT" != "$DIR" ] && [ "$MNTPNT" == "$WITHOUT_DIR" -o "${WITHOUT_DIR::1}" != "/" ] && continue
+ MNTTYPE="$(echo "${LINE}" | awk '{print $3}')"
+ [ "${MNTTYPE}" = "ext4" ] && continue
+ [ "${MNTTYPE}" = "tmpfs" ] && continue
+ MNTOPTS="$(echo "${LINE}" | awk '{print $4}')"
+ echo "mount -t ${MNTTYPE} -o ${MNTOPTS} ${MNTDEV} ${MNTPNT}" >>/mnt/data/mnt.sh
+ # Before mv, unmount filesystems (virtiofs, 9p, etc.) below "${DIR}", otherwise host mounts will be wiped out
+ # https://github.com/rancher-sandbox/rancher-desktop/issues/6582
+ umount "${MNTPNT}" || exit 1
+ done </proc/mounts
  mv "${DIR}" "${DEST}"
  done
+ chmod +x /mnt/data/mnt.sh
  # Make sure all data moved to the persistent volume has been committed to disk
  sync
  break
@@ -88,8 +109,8 @@ if [ "$(awk '$2 == "/" {print $3}' /proc/mounts)" == "tmpfs" ]; then
  mount --bind /mnt/data"${DIR}" "${DIR}"
  fi
  done
- # Make sure to re-mount any mount points under /tmp
- mount -a
+ # Remount submounts on top of the new ${DIR}
+ /mnt/data/mnt.sh
  # Reinstall packages from /mnt/data/apk/cache into the RAM disk
  apk fix --no-network
 fi