linux-kernel - Re: [syzbot] [overlayfs?] WARNING in ovl_copy_up

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Date: Wed, 13 Mar 2024 22:55:06 +0200
From: Amir Goldstein <amir73il@...il.com>
To: miklos@...redi.hu
Cc: linux-fsdevel@...r.kernel.org, linux-kernel@...r.kernel.org, 
	linux-unionfs@...r.kernel.org, syzkaller-bugs@...glegroups.com, 
	syzbot <syzbot+3abd99031b42acf367ef@...kaller.appspotmail.com>
Subject: Re: [syzbot] [overlayfs?] WARNING in ovl_copy_up_file

On Wed, Mar 13, 2024 at 12:23 PM syzbot
<syzbot+3abd99031b42acf367ef@...kaller.appspotmail.com> wrote:
>
> Hello,
>
> syzbot found the following issue on:
>
> HEAD commit:    707081b61156 Merge branch 'for-next/core', remote-tracking..
> git tree:       git://git.kernel.org/pub/scm/linux/kernel/git/arm64/linuxgit for-kernelci
> console output: https://syzkaller.appspot.com/x/log.txt?x=1785a859180000
> kernel config:  https://syzkaller.appspot.com/x/.config?x=caeac3f3565b057a
> dashboard link: https://syzkaller.appspot.com/bug?extid=3abd99031b42acf367ef
> compiler:       Debian clang version 15.0.6, GNU ld (GNU Binutils for Debian) 2.40
> userspace arch: arm64
> syz repro:      https://syzkaller.appspot.com/x/repro.syz?x=1115ada6180000
> C reproducer:   https://syzkaller.appspot.com/x/repro.c?x=1626870a180000
>
> Downloadable assets:
> disk image: https://storage.googleapis.com/syzbot-assets/6cad68bf7532/disk-707081b6.raw.xz
> vmlinux: https://storage.googleapis.com/syzbot-assets/1a27e5400778/vmlinux-707081b6.xz
> kernel image: https://storage.googleapis.com/syzbot-assets/67dfc53755d0/Image-707081b6.gz.xz
>
> IMPORTANT: if you fix the issue, please add the following tag to the commit:
> Reported-by: syzbot+3abd99031b42acf367ef@...kaller.appspotmail.com
>
> evm: overlay not supported
> ------------[ cut here ]------------
> WARNING: CPU: 0 PID: 6187 at fs/overlayfs/copy_up.c:239 ovl_copy_up_file+0x624/0x674 fs/overlayfs/copy_up.c:330

Miklos,

The WARN_ON that I put in ovl_verify_area() may be too harsh.
I think they can happen if lower file is changed (i_size) while file is being
copied up after reading i_size into the copy length and this could be
the case with this syzbot reproducer that keeps mounting overlayfs
instances over same path.

Should probably demote those WARN_ON to just returning EIO?

Thanks,
Amir.