linux-kernel - Re: [syzbot] [btrfs?] [overlayfs?] possible deadlock in ovl_copy_up

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Date: Thu, 23 May 2024 18:43:12 +0200
From: David Sterba <dsterba@...e.cz>
To: syzbot <syzbot+85e58cdf5b3136471d4b@...kaller.appspotmail.com>
Cc: amir73il@...il.com, brauner@...nel.org, clm@...com, dsterba@...e.com,
	jack@...e.cz, josef@...icpanda.com, linux-btrfs@...r.kernel.org,
	linux-fsdevel@...r.kernel.org, linux-kernel@...r.kernel.org,
	linux-unionfs@...r.kernel.org, miklos@...redi.hu,
	mszeredi@...hat.com, syzkaller-bugs@...glegroups.com,
	viro@...iv.linux.org.uk
Subject: Re: [syzbot] [btrfs?] [overlayfs?] possible deadlock in
 ovl_copy_up_flags

On Thu, May 23, 2024 at 03:09:26AM -0700, syzbot wrote:
> Hello,
> 
> syzbot found the following issue on:
> 
> HEAD commit:    c75962170e49 Add linux-next specific files for 20240517
> git tree:       linux-next
> console+strace: https://syzkaller.appspot.com/x/log.txt?x=1438a5cc980000
> kernel config:  https://syzkaller.appspot.com/x/.config?x=fba88766130220e8
> dashboard link: https://syzkaller.appspot.com/bug?extid=85e58cdf5b3136471d4b
> compiler:       Debian clang version 15.0.6, GNU ld (GNU Binutils for Debian) 2.40
> syz repro:      https://syzkaller.appspot.com/x/repro.syz?x=115f3e58980000
> C reproducer:   https://syzkaller.appspot.com/x/repro.c?x=14f4c97c980000
> 
> Downloadable assets:
> disk image: https://storage.googleapis.com/syzbot-assets/21696f8048a3/disk-c7596217.raw.xz
> vmlinux: https://storage.googleapis.com/syzbot-assets/b8c71f928633/vmlinux-c7596217.xz
> kernel image: https://storage.googleapis.com/syzbot-assets/350bfc6c0a6a/bzImage-c7596217.xz
> mounted in repro: https://storage.googleapis.com/syzbot-assets/7f6a8434331c/mount_0.gz
> 
> The issue was bisected to:
> 
> commit 9a87907de3597a339cc129229d1a20bc7365ea5f
> Author: Miklos Szeredi <mszeredi@...hat.com>
> Date:   Thu May 2 18:35:57 2024 +0000
> 
>     ovl: implement tmpfile

In the C reproducer it's btrfs + overlayfs, this more looks like a bug in
overlayfs handling the tmpfile and sb_*_write accross layers. Btrfs
functions are not on the stack.

#syz set subsystems: overlayfs