linux-kernel - Re: [syzbot] KASAN: use-after-free Read in z_erofs_transform

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Message-ID: <Y426Mo9cweiBi77q@B-P7TQMD6M-0146.local>
Date:   Mon, 5 Dec 2022 17:30:26 +0800
From:   Gao Xiang <hsiangkao@...ux.alibaba.com>
To:     syzbot <syzbot+2ae90e873e97f1faf6f2@...kaller.appspotmail.com>
Cc:     chao@...nel.org, huyue2@...lpad.com, jefflexu@...ux.alibaba.com,
        linux-erofs@...ts.ozlabs.org, linux-kernel@...r.kernel.org,
        syzkaller-bugs@...glegroups.com, xiang@...nel.org
Subject: Re: [syzbot] KASAN: use-after-free Read in z_erofs_transform_plain

On Mon, Dec 05, 2022 at 12:13:47AM -0800, syzbot wrote:
> Hello,
> 
> syzbot found the following issue on:
> 
> HEAD commit:    97ee9d1c1696 Merge tag 'block-6.1-2022-12-02' of git://git..
> git tree:       upstream
> console output: https://syzkaller.appspot.com/x/log.txt?x=1786b2f5880000
> kernel config:  https://syzkaller.appspot.com/x/.config?x=2325e409a9a893e1
> dashboard link: https://syzkaller.appspot.com/bug?extid=2ae90e873e97f1faf6f2
> compiler:       Debian clang version 13.0.1-++20220126092033+75e33f71c2da-1~exp1~20220126212112.63, GNU ld (GNU Binutils for Debian) 2.35.2
> syz repro:      https://syzkaller.appspot.com/x/repro.syz?x=115e5c47880000
> C reproducer:   https://syzkaller.appspot.com/x/repro.c?x=170fa3d5880000
> 
> Downloadable assets:
> disk image: https://storage.googleapis.com/syzbot-assets/6a6a9ff34dfa/disk-97ee9d1c.raw.xz
> vmlinux: https://storage.googleapis.com/syzbot-assets/2a01a4182c2b/vmlinux-97ee9d1c.xz
> kernel image: https://storage.googleapis.com/syzbot-assets/4371158e8c25/bzImage-97ee9d1c.xz
> mounted in repro: https://storage.googleapis.com/syzbot-assets/22dcea976d97/mount_0.gz
> 

It seems another report due to mixed ztailpacking (inline) and
non-inlined pclusters at once.

(Although I need to add another check for mixed algorithm formats for
 a single pcluster as well..)

#syz fix: erofs: Fix pcluster memleak when its block address is zero 

> The issue was bisected to:
> 
> commit dcbe6803fffd387f72b48c2373b5f5ed12a5804b
> Author: Gao Xiang <hsiangkao@...ux.alibaba.com>
> Date:   Thu May 12 11:58:33 2022 +0000
> 
>     erofs: fix buffer copy overflow of ztailpacking feature
> 

It caused KASAN to begin to report, but it's not the root cause. Just
ignore it.

Thanks,
Gao Xiang