ncpfs: fix rename over directory with dangling references

ncpfs does not handle references to unlinked directories (or so it would
seem given the ncp_rmdir check).  Since it is also possible to rename over
an empty directory, perform the same check here.

CC: Petr Vandrovec <petr@vandrovec.name>
CC: linux-kernel@vger.kernel.org
Signed-off-by: Sage Weil <sage@newdream.net>
Signed-off-by: Al Viro <viro@zeniv.linux.org.uk>

fs/ncpfs/dir.c

@@ -1144,8 +1144,16 @@ static int ncp_rename(struct inode *old_dir, struct dentry *old_dentry,
 		old_dentry->d_parent->d_name.name, old_dentry->d_name.name,
 		new_dentry->d_parent->d_name.name, new_dentry->d_name.name);
 
-	if (new_dentry->d_inode && S_ISDIR(new_dentry->d_inode->i_mode))
+	if (new_dentry->d_inode && S_ISDIR(new_dentry->d_inode->i_mode)) {
+		/*
+		 * fail with EBUSY if there are still references to this
+		 * directory.
+		 */
 		dentry_unhash(new_dentry);
+		error = -EBUSY;
+		if (!d_unhashed(new_dentry))
+			goto out;
+	}
 
 	ncp_age_dentry(server, old_dentry);
 	ncp_age_dentry(server, new_dentry);