dracut.sh: don't call fsfreeze on subvol of root file system

dracut.sh already doesn't call fsfreeze if the output file is on
the root file system. For btrfs, however, this is not sufficient.
Because fsfreeze is a superblock operation, and all btrfs subvolumes
share the same superblock, fsfreeze may freeze the entire system
if the subvolume on which the output file is written and / are
subvolumes of the same file system. Avoid this by comparing file
system UUIDs for btrfs.

Fixes: de576db3c225 ("call fsfreeze(8) on /boot to flush initramfs data & metadata to media")

diff --git a/dracut.sh b/dracut.sh
index af346f3a2614bab1ccf4f391832bc5d26f03190c..c14f6c0bd4117c6a510093293a0e83fb8caf05b4 100755 (executable)
--- a/dracut.sh
+++ b/dracut.sh
@@ -2075,6 +2075,40 @@ fi
 
 command -v restorecon &>/dev/null && restorecon -- "$outfile"
 
+btrfs_uuid() {
+    btrfs filesystem show "$1" | sed -n '1s/^.*uuid: //p'
+}
+
+freeze_ok_for_btrfs() {
+    local mnt uuid1 uuid2
+    # If the output file is on btrfs, we need to make sure that it's
+    # not on a subvolume of the same file system as the root FS.
+    # Otherwise, fsfreeze() might freeze the entire system.
+    # This is most conveniently checked by comparing the FS uuid.
+
+    [[ "$(stat -f -c %T -- "/")" == "btrfs" ]] || return 0
+    mnt=$(stat -c %m -- "$1")
+    uuid1=$(btrfs_uuid "$mnt")
+    uuid2=$(btrfs_uuid "/")
+    [[ "$uuid1" && "$uuid2" && "$uuid1" != "$uuid2" ]]
+}
+
+freeze_ok_for_fstype() {
+    local outfile=$1
+    local fstype
+
+    [[ "$(stat -c %m -- "$outfile")" == "/" ]] && return 1
+    fstype=$(stat -f -c %T -- "$outfile")
+    case $fstype in
+        msdos)
+            return 1;;
+        btrfs)
+            freeze_ok_for_btrfs "$outfile";;
+        *)
+            return 0;;
+    esac
+}
+
 # We sync/fsfreeze only if we're operating on a live booted system.
 # It's possible for e.g. `kernel` to be installed as an RPM BuildRequires or equivalent,
 # and there's no reason to sync, and *definitely* no reason to fsfreeze.
@@ -2087,7 +2121,7 @@ if test -d $dracutsysrootdir/run/systemd/system; then
     fi
 
     # use fsfreeze only if we're not writing to /
-    if [[ "$(stat -c %m -- "$outfile")" != "/" && "$(stat -f -c %T -- "$outfile")" != "msdos" ]]; then
+    if [[ "$(stat -c %m -- "$outfile")" != "/" ]] && freeze_ok_for_fstype "$outfile"; then
         if ! $(fsfreeze -f $(dirname "$outfile") 2>/dev/null && fsfreeze -u $(dirname "$outfile") 2>/dev/null); then
             dinfo "dracut: warning: could not fsfreeze $(dirname "$outfile")"
         fi