ovl: don't remove non-empty opaque directory

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@gmail.com>
Signed-off-by: Miklos Szeredi <mszeredi@suse.cz>
Tested-by: Jordi Pujol Palomer <jordipujolp@gmail.com>
Fixes: 263b4a0fee43 ("ovl: dont replace opaque dir")
Cc: <stable@vger.kernel.org> # v4.0+

1 files changed, 19 insertions, 5 deletions

diff --git a/fs/overlayfs/dir.c b/fs/overlayfs/dir.c
index d139405d2bfa..2578a0c0677d 100644
--- a/fs/overlayfs/dir.c
+++ b/fs/overlayfs/dir.c
@@ -506,11 +506,25 @@ static int ovl_remove_and_whiteout(struct dentry *dentry, bool is_dir)
         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);