ubifs: do_rename: Fix wrong space budget when target inode's nlink > 1

If target inode is a special file (eg. block/char device) with nlink
count greater than 1, the inode with ui->data will be re-written on
disk. However, UBIFS losts target inode's data_len while doing space
budget. Bad space budget may let make_reservation() return with -ENOSPC,
which could turn ubifs to read-only mode in do_writepage() process.

Fetch a reproducer in [Link].

Link: https://bugzilla.kernel.org/show_bug.cgi?id=216494
Fixes: 1e51764 ("UBIFS: add new flash file system")
Signed-off-by: Zhihao Cheng <[email protected]>
Signed-off-by: Richard Weinberger <[email protected]>

Author: Zhihao Cheng

fs/ubifs/dir.c

@@ -1324,6 +1324,8 @@ static int do_rename(struct inode *old_dir, struct dentry *old_dentry,
 	if (unlink) {
 		ubifs_assert(c, inode_is_locked(new_inode));
 
+		/* Budget for old inode's data when its nlink > 1. */
+		req.dirtied_ino_d = ALIGN(ubifs_inode(new_inode)->data_len, 8);
 		err = ubifs_purge_xattrs(new_inode);
 		if (err)
 			return err;