linux-kernel - Re: [PATCH] acct: Prevent NULL pointer dereference when writing to sysfs

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Message-ID: <20250210-erstsemester-eckpunkte-f2f0d922ed01@brauner>
Date: Mon, 10 Feb 2025 17:02:35 +0100
From: Christian Brauner <brauner@...nel.org>
To: Al Viro <viro@...iv.linux.org.uk>
Cc: Zicheng Qu <quzicheng@...wei.com>, 
	Linus Torvalds <torvalds@...ux-foundation.org>, jlayton@...nel.org, axboe@...nel.dk, joel.granados@...nel.org, 
	tglx@...utronix.de, linux-kernel@...r.kernel.org, hch@....de, len.brown@...el.com, 
	pavel@....cz, pengfei.xu@...el.com, rafael@...nel.org, 
	syzkaller-bugs@...glegroups.com, linux-pm@...r.kernel.org, tanghui20@...wei.com, 
	zhangqiao22@...wei.com, judy.chenhui@...wei.com
Subject: Re: [PATCH] acct: Prevent NULL pointer dereference when writing to
 sysfs

On Mon, Feb 10, 2025 at 03:21:46PM +0000, Al Viro wrote:
> On Mon, Feb 10, 2025 at 04:12:54PM +0100, Christian Brauner wrote:
> 
> > One fix would be to move exit_fs() past exit_task_work(). It looks like
> > that this should be doable without much of a problem and it would fix
> > the path_init() problem.
> > 
> > There should hopefully be nothing relying on task->fs == NULL in
> > exit_task_work().
> 
> There's a question of the task_work_add() issued by exit_task_fs(),
> though.

Can't we simply remove the pins on the mounts of fs->root and fs->pwd in
exit_fs() explicitly? If that works I think that's a fair enough
compromise for this shite.