linux-kernel - Re: VFS: Close: file count is zero (use-after-free)

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Date: Mon, 18 Mar 2024 10:31:32 +0100
From: Christian Brauner <brauner@...nel.org>
To: cheung wall <zzqq0103.hey@...il.com>
Cc: Alexander Viro <viro@...iv.linux.org.uk>, Jan Kara <jack@...e.cz>, 
	linux-fsdevel@...r.kernel.org, linux-kernel@...r.kernel.org
Subject: Re: VFS: Close: file count is zero (use-after-free)

On Sun, Mar 17, 2024 at 07:57:28PM +0800, cheung wall wrote:
> Hello,
> 
> when using Healer to fuzz the latest Linux Kernel, the following crash
> 
> was triggered on:
> 
> 
> HEAD commit: e8f897f4afef0031fe618a8e94127a0934896aba  (tag: v6.8)
> 
> git tree: upstream
> 
> console output: https://pastebin.com/raw/nWDbVZij

Generally it's not great to have ever more fuzzer generated reports
outside of the official syzbot reports.

And fwiw, your link isn't even accessible.

> 
> kernel config: https://pastebin.com/raw/4m4ax5gq
> 
> C reproducer: https://pastebin.com/raw/0ZSaae7K

That program seemingly to the mounted block device and your config has
CONFIG_BLK_DEV_WRITE_MOUNTED=y causing corruption. So that bug is likely
caused by that. Set CONFIG_BLK_DEV_WRITE_MOUNTED=n for your testbot.