linux-kernel - [PATCH] nlink overflow in jfs

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Message-ID: <20251118163926.65737-1-jkoolstra@xs4all.nl>
Date: Tue, 18 Nov 2025 17:39:26 +0100
From: Jori Koolstra <jkoolstra@...all.nl>
To: brauner@...nel.org,
	gabriel@...sman.be,
	jlayton@...nel.org,
	neil@...wn.name,
	shaggy@...nel.org,
	viro@...iv.linux.org.uk
Cc: jkoolstra@...all.nl,
	jfs-discussion@...ts.sourceforge.net,
	linux-kernel@...r.kernel.org,
	syzbot+9131ddfd7870623b719f@...kaller.appspotmail.com,
	skhan@...uxfoundation.org
Subject: [PATCH] nlink overflow in jfs_rename

Below syzbot bug has not been fixed yet. If anyone has time I would
greatly appreciate a review of my patch, so it can be moved along.
It has been sitting for a few weeks.

Thanks,
Jori.

Apologies for the resend, I messed up the email headers.

> Op 28-10-2025 13:22 CET schreef Jori Koolstra <jkoolstra@...all.nl>:
>
>
> If nlink is maximal for a directory (-1) and inside that directory you
> perform a rename for some child directory (not moving from the parent),
> then the nlink of the first directory is first incremented and later
> decremented. Normally this is fine, but when nlink = -1 this causes a
> wrap around to 0, and then drop_nlink issues a warning.
> 
> After applying the patch syzbot no longer issues any warnings. I also
> ran some basic fs tests to look for any regressions.
> 
> Signed-off-by: Jori Koolstra <jkoolstra@...all.nl>
> Reported-by: syzbot+9131ddfd7870623b719f@...kaller.appspotmail.com
> Closes: https://syzbot.org/bug?extid=9131ddfd7870623b719f