[PATCH] ovl: check for emptiness of redirect dir

[Amir Goldstein <amir73il@gmail.com>]

Before introducing redirect_dir feature, the condition
!ovl_lower_positive(dentry) for a directory, implied that
it is a pure upper directory, which may be removed if empty.

Now that directory can be redirect, it is possible that
upper does not cover any lower (i.e. !ovl_lower_positive(dentry)),
but the directory is a merge (with redirected path) and maybe
non empty.

Check for this case in ovl_remove_upper().

This change fixes the following test case from rename-pop-dir.py
of unionmount-testsuite:

    """Remove dir and rename old name"""
    d = ctx.non_empty_dir()
    d2 = ctx.no_dir()

    ctx.rmdir(d, err=ENOTEMPTY)
    ctx.rename(d, d2)
    ctx.rmdir(d, err=ENOENT)
    ctx.rmdir(d2, err=ENOTEMPTY)

./run --ov rename-pop-dir
/mnt/a/no_dir103: Expected error (Directory not empty) was not produced

Signed-off-by: Amir Goldstein <amir73il@gmail.com>
---
 fs/overlayfs/dir.c | 31 ++++++++++++++++++++++---------
 1 file changed, 22 insertions(+), 9 deletions(-)

diff --git a/fs/overlayfs/dir.c b/fs/overlayfs/dir.c
index 065e021..d750ed9 100644
--- a/fs/overlayfs/dir.c
+++ b/fs/overlayfs/dir.c
@@ -672,9 +672,18 @@ static int ovl_remove_upper(struct dentry *dentry, bool is_dir)
 {
 	struct dentry *upperdir = ovl_dentry_upper(dentry->d_parent);
 	struct inode *dir = upperdir->d_inode;
-	struct dentry *upper;
+	struct dentry *upper = NULL;
+	struct dentry *opaquedir = NULL;
 	int err;
 
+	/* Redirect dir can be !ovl_lower_positive && OVL_TYPE_MERGE */
+	if (is_dir && ovl_dentry_is_redirect(dentry)) {
+		opaquedir = ovl_check_empty_and_clear(dentry);
+		err = PTR_ERR(opaquedir);
+		if (IS_ERR(opaquedir))
+			return err;
+	}
+
 	inode_lock_nested(dir, I_MUTEX_PARENT);
 	upper = lookup_one_len(dentry->d_name.name, upperdir,
 			       dentry->d_name.len);
@@ -683,14 +692,15 @@ static int ovl_remove_upper(struct dentry *dentry, bool is_dir)
 		goto out_unlock;
 
 	err = -ESTALE;
-	if (upper == ovl_dentry_upper(dentry)) {
-		if (is_dir)
-			err = vfs_rmdir(dir, upper);
-		else
-			err = vfs_unlink(dir, upper, NULL);
-		ovl_dentry_version_inc(dentry->d_parent);
-	}
-	dput(upper);
+	if ((opaquedir && upper != opaquedir) ||
+	     upper != ovl_dentry_upper(dentry))
+		goto out_dput_upper;
+
+	if (is_dir)
+		err = vfs_rmdir(dir, upper);
+	else
+		err = vfs_unlink(dir, upper, NULL);
+	ovl_dentry_version_inc(dentry->d_parent);
 
 	/*
 	 * Keeping this dentry hashed would mean having to release
@@ -700,8 +710,11 @@ static int ovl_remove_upper(struct dentry *dentry, bool is_dir)
 	 */
 	if (!err)
 		d_drop(dentry);
+out_dput_upper:
+	dput(upper);
 out_unlock:
 	inode_unlock(dir);
+	dput(opaquedir);
 
 	return err;
 }
-- 
2.7.4