linux-kernel - Re: [PATCH v1] xfs: prevent readdir infinite loop with billions subdirs

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Message-ID: <aJnHw78dwyEL4F7U@infradead.org>
Date: Mon, 11 Aug 2025 03:36:51 -0700
From: Christoph Hellwig <hch@...radead.org>
To: liuhuan01@...inos.cn
Cc: cem@...nel.org, djwong@...nel.org, linux-xfs@...r.kernel.org,
	linux-kernel@...r.kernel.org
Subject: Re: [PATCH v1] xfs: prevent readdir infinite loop with billions
 subdirs

On Fri, Aug 01, 2025 at 04:41:46PM +0800, liuhuan01@...inos.cn wrote:
> From: liuh <liuhuan01@...inos.cn>
> 
> When a directory contains billions subdirs, readdir() repeatedly
> got same data and goes to infinate loop.
> The root cause is that the pos gets truncated during assignment.
> Fix it.

This got added in:

15440319767942a363f282d6585303d3d75088ba
Author: Christoph Hellwig <hch@...radead.org>
Date:   Thu Jan 8 14:00:00 2009 -0500

    [XFS] truncate readdir offsets to signed 32 bit values

I promised to come up with something better back them, but I could for
the fear of my life not remember what that would be.

I guess the most compatible thing we could do would be to make the
truncation dependent on is_compat_task().  You'd still get the same
issue on 32-bit systems, but I don't really see what else we could
do for them.