[PATCH 2/2] mount-copybind: add MOUNT_COPYBIND_AVOID_OVERLAYFS env var to skip OverlayFS

[luca.boccassi@gmail.com]

From: Luca Boccassi <luca.boccassi@microsoft.com>

In some cases we don't want to even attempt to set up OverlayFS, for
example because SELinux in enforcing mode would kill the process
attempting to use the mount. See:

https://lore.kernel.org/all/CA+FmFJBDwt52Z-dVGfuUcnRMiMtGPhK4cCQJ=J_fg0r3x-b6ng@mail.gmail.com/T/#mef98aa406324096d1889d3d467251f30456f403c

If MOUNT_COPYBIND_AVOID_OVERLAYFS=1 is set, skip directly to copy and
bind mount.

Signed-off-by: Luca Boccassi <luca.boccassi@microsoft.com>
---
 meta/recipes-core/volatile-binds/files/mount-copybind | 5 ++++-
 1 file changed, 4 insertions(+), 1 deletion(-)

diff --git a/meta/recipes-core/volatile-binds/files/mount-copybind b/meta/recipes-core/volatile-binds/files/mount-copybind
index 8bbb406b3a..ddc4357615 100755
--- a/meta/recipes-core/volatile-binds/files/mount-copybind
+++ b/meta/recipes-core/volatile-binds/files/mount-copybind
@@ -2,6 +2,9 @@
 #
 # Perform a bind mount, copying existing files as we do so to ensure the
 # overlaid path has the necessary content.
+# If the target is a directory and overlayfs is available (and the environment
+# variable MOUNT_COPYBIND_AVOID_OVERLAYFS=1 is not set), then an overlay mount
+# will be attempted first.
 
 if [ $# -lt 2 ]; then
     echo >&2 "Usage: $0 spec mountpoint [OPTIONS]"
@@ -51,7 +54,7 @@ if [ -d "$mountpoint" ]; then
             mountcontext=",rootcontext=$(matchpathcon -n "$mountpoint")"
         fi
     fi
-    if ! mount -t overlay overlay -olowerdir="$mountpoint",upperdir="$spec",workdir="$overlay_workdir""$mountcontext" "$mountpoint" > /dev/null 2>&1; then
+    if [ "$MOUNT_COPYBIND_AVOID_OVERLAYFS" = 1 ] || ! mount -t overlay overlay -olowerdir="$mountpoint",upperdir="$spec",workdir="$overlay_workdir""$mountcontext" "$mountpoint" > /dev/null 2>&1; then
 
         if [ "$specdir_existed" != "yes" ]; then
             cp -aPR "$mountpoint"/. "$spec/"
-- 
2.34.1