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

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Message-ID: <00bbda63-dc00-05c0-4244-343352591d98@gmx.com>
Date:   Thu, 16 Jun 2022 05:27:04 +0800
From:   Qu Wenruo <quwenruo.btrfs@....com>
To:     Christoph Hellwig <hch@....de>
Cc:     dsterba@...e.cz,
        syzbot <syzbot+d2dd123304b4ae59f1bd@...kaller.appspotmail.com>,
        akpm@...ux-foundation.org, clm@...com, dsterba@...e.com,
        josef@...icpanda.com, linux-btrfs@...r.kernel.org,
        linux-fsdevel@...r.kernel.org, linux-kernel@...r.kernel.org,
        linux-mm@...ck.org, syzkaller-bugs@...glegroups.com,
        willy@...radead.org
Subject: Re: [syzbot] KASAN: use-after-free Read in copy_page_from_iter_atomic
 (2)



On 2022/6/15 21:21, Christoph Hellwig wrote:
> On Tue, Jun 14, 2022 at 04:50:22PM +0800, Qu Wenruo wrote:
>> The same way as data?
>>
>> map-logical to find the location of a mirror, write 4 bytes of zero into
>> the location, then call it a day.
>>
>> Although for metadata, you may want to choose a metadata that would
>> definitely get read.
>> Thus tree root is a good candidate.
>
> And how do I find out the logic address of the tree root?

For tree root, "btrfs ins dump-super <dev> | grep '^root\s'.

For other tree blocks, "btrfs ins dump-tree <dev>" then with other other
keywords to grab.

Thanks,
Qu