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Date: Mon, 11 Dec 2023 21:35:37 -0800
From: Christoph Hellwig <hch@infradead.org>
To: "Darrick J. Wong" <djwong@kernel.org>
Cc: Christoph Hellwig <hch@infradead.org>, linux-xfs@vger.kernel.org
Subject: Re: [PATCH 9/9] xfs: repair obviously broken inode modes
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On Mon, Dec 11, 2023 at 02:19:26PM -0800, Darrick J. Wong wrote:
> block/char/special files... I guess those can just turn into zero length
> regular files.

Ys, and I don't think that is much of a problem.

> Would this NAK remain even if there were external corroborating
> evidence?
> 
> For example, what if we read the dirents out of the first directory
> block, seek out parent pointers in the alleged children, and confirm a
> 1:1 match between the alleged dirents and pptrs?  Unprivileged userspace
> can certain create a regular file N that looks like a dirent block, but
> it cannot create dangling pptrs back to N to trick the verification
> algorithm.

That does look like I a good enough evinde as you said userspace can't
fake up the parent pointer.