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

Signed-off-by: Akihiro Suda <akihiro.suda.cz@hco.ntt.co.jp>

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

@@ -61,21 +61,37 @@ 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 $2}' | sed -e 's/\\040/ /g; s/\\011/\t/g; s/\\012/\n/g; s/\\134/\\/g; s/\\043/#/g')"
+						# This comparison needs [[, not [
+						[[ "${MNTPNT}" != "${DIR}*" ]] && continue
+						MNTTYPE="$(echo "${LINE}" | awk '{print $3}')"
+						[ "${MNTTYPE}" = "ext4" ] && continue
+						[ "${MNTTYPE}" = "tmpfs" ] && continue
+						MNTOPTS="$(echo "${LINE}" | awk '{print $4}')"
+						echo "mount -t ${MNTTYPE} -o ${MNTOPTS} ${MNTDEV} ${MNTPNT}" >>/mnt.tmp.sh
+						# Before mv, unmount filesystems (virtiofs, 9p, etc.) below "${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}" "${DEST}"
 				done
+				chmod +x /mnt/data/mnt.sh
 				# Make sure all data moved to the persistent volume has been committed to disk
 				sync
 				break
@@ -88,8 +104,8 @@ if [ "$(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.tmp.sh
 	# Reinstall packages from /mnt/data/apk/cache into the RAM disk
 	apk fix --no-network
 fi