[PATCH 4.0 019/148] ovl: dont remove non-empty opaque directory

[Greg Kroah-Hartman]

4.0-stable review patch.  If anyone has any objections, please let me know.

------------------

From: Miklos Szeredi <mszeredi@xxxxxxx>

commit d377c5eb54dd05aeb3094b7740252d19ba7791f7 upstream.

When removing an opaque directory we can't just call rmdir() to check for
emptiness, because the directory will need to be replaced with a whiteout.
The replacement is done with RENAME_EXCHANGE, which doesn't check
emptiness.

Solution is just to check emptiness by reading the directory.  In the
future we could add a new rename flag to check for emptiness even for
RENAME_EXCHANGE to optimize this case.

Reported-by: Vincent Batts <vbatts@xxxxxxxxx>
Signed-off-by: Miklos Szeredi <mszeredi@xxxxxxx>
Tested-by: Jordi Pujol Palomer <jordipujolp@xxxxxxxxx>
Fixes: 263b4a0fee43 ("ovl: dont replace opaque dir")
Signed-off-by: Greg Kroah-Hartman <gregkh@xxxxxxxxxxxxxxxxxxx>

---
 fs/overlayfs/dir.c |   24 +++++++++++++++++++-----
 1 file changed, 19 insertions(+), 5 deletions(-)

--- a/fs/overlayfs/dir.c
+++ b/fs/overlayfs/dir.c
@@ -506,11 +506,25 @@ static int ovl_remove_and_whiteout(struc
 	struct dentry *opaquedir = NULL;
 	int err;
 
-	if (is_dir && OVL_TYPE_MERGE_OR_LOWER(ovl_path_type(dentry))) {
-		opaquedir = ovl_check_empty_and_clear(dentry);
-		err = PTR_ERR(opaquedir);
-		if (IS_ERR(opaquedir))
-			goto out;
+	if (is_dir) {
+		if (OVL_TYPE_MERGE_OR_LOWER(ovl_path_type(dentry))) {
+			opaquedir = ovl_check_empty_and_clear(dentry);
+			err = PTR_ERR(opaquedir);
+			if (IS_ERR(opaquedir))
+				goto out;
+		} else {
+			LIST_HEAD(list);
+
+			/*
+			 * When removing an empty opaque directory, then it
+			 * makes no sense to replace it with an exact replica of
+			 * itself.  But emptiness still needs to be checked.
+			 */
+			err = ovl_check_empty_dir(dentry, &list);
+			ovl_cache_free(&list);
+			if (err)
+				goto out;
+		}
 	}
 
 	err = ovl_lock_rename_workdir(workdir, upperdir);


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