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 9p (reverse-sshfs is not affected)
- 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 <jan.dubois@suse.com>
Signed-off-by: Akihiro Suda <akihiro.suda.cz@hco.ntt.co.jp>

.github/workflows/test.yml

@@ -225,6 +225,7 @@ jobs:
         - opensuse.yaml
         - experimental/net-user-v2.yaml
         - docker.yaml
+        - ../hack/test-templates/alpine-9p-writable.yaml
     steps:
     - uses: actions/checkout@v4
       with:
@@ -258,6 +259,8 @@ jobs:
         retry_on: error
         max_attempts: 3
         command: ./hack/test-templates.sh templates/${{ matrix.template }}
+    - name: "Check that the host home is not wiped"
+      run: test -e ~/.cache/lima
     - name: "Show cache"
       run: ./hack/debug-cache.sh
 

hack/test-templates.sh

@@ -37,7 +37,7 @@ declare -A CHECKS=(
 )
 
 case "$NAME" in
-"alpine")
+"alpine"*)
 	WARNING "Alpine does not support systemd"
 	CHECKS["systemd"]=
 	CHECKS["container-engine"]=

hack/test-templates/alpine-9p-writable.yaml

@@ -0,0 +1,18 @@
+# Background: https://github.com/lima-vm/lima/pull/2234
+# Should be tested on a Linux host
+images:
+- location: "https://github.com/lima-vm/alpine-lima/releases/download/v0.2.37/alpine-lima-std-3.19.0-x86_64.iso"
+  arch: "x86_64"
+  digest: "sha512:568852df405e6b9858e678171a9894c058f483df0b0570c22cf33fc75f349ba6cc5bb3d50188180d8c31faaf53400fe884ca3e5f949961b03b2bf53e65de88d7"
+- location: "https://github.com/lima-vm/alpine-lima/releases/download/v0.2.37/alpine-lima-std-3.19.0-aarch64.iso"
+  arch: "aarch64"
+  digest: "sha512:3a4bd5ad0201f503e9bb9f3b812aa0df292e2e099148c0323d23244046ad199a2946ef9e0619fec28726bfdcc528233f43c3b4b036c9e06e92ac730d579f0ca3"
+
+mountType: "9p"
+mounts:
+- location: "~"
+  writable: true
+
+containerd:
+  system: false
+  user: false

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

@@ -9,6 +9,34 @@ test -f /etc/alpine-release || exit 0
 # Data directories that should be persisted across reboots
 DATADIRS="/etc /home /root /tmp /usr/local /var/lib"
 
+# Prepare mnt.sh (used for restoring mounts later)
+echo "#!/bin/sh" >/mnt.sh
+echo "set -eux" >>/mnt.sh
+for DIR in ${DATADIRS}; do
+	while IFS= read -r LINE; do
+		[ -z "$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 $2}' | sed -e 's/\\040/ /g; s/\\011/\t/g; s/\\012/\n/g; s/\\134/\\/g; s/\\043/#/g')"
+		# Ignore if MNTPNT is neither DIR nor a parent directory of DIR.
+		# It is not a parent if MNTPNT doesn't start with DIR, or the first
+		# character after DIR isn't a slash.
+		WITHOUT_DIR="${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} ${MNTPNT}" >>/mnt.sh
+		# Before mv, unmount filesystems (virtiofs, 9p, etc.) below "${DIR}", otherwise host mounts will be wiped out
+		# https://github.com/rancher-sandbox/rancher-desktop/issues/6582
+		umount "${MNTPNT}" || exit 1
+	done </proc/mounts
+done
+chmod +x /mnt.sh
+
 # When running from RAM try to move persistent data to data-volume
 # FIXME: the test for tmpfs mounts is probably Alpine-specific
 if [ "$(awk '$2 == "/" {print $3}' /proc/mounts)" == "tmpfs" ]; then
@@ -61,11 +89,6 @@ if [ "$(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
@@ -88,8 +111,8 @@ 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.sh
 	# Reinstall packages from /mnt/data/apk/cache into the RAM disk
 	apk fix --no-network
 fi