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Date:   Thu, 16 Jun 2022 05:27:04 +0800
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Subject: Re: [syzbot] KASAN: use-after-free Read in copy_page_from_iter_atomic
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To:     Christoph Hellwig <hch@lst.de>
Cc:     dsterba@suse.cz,
        syzbot <syzbot+d2dd123304b4ae59f1bd@syzkaller.appspotmail.com>,
        akpm@linux-foundation.org, clm@fb.com, dsterba@suse.com,
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        linux-fsdevel@vger.kernel.org, linux-kernel@vger.kernel.org,
        linux-mm@kvack.org, syzkaller-bugs@googlegroups.com,
        willy@infradead.org
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 <20220615132147.GA18252@lst.de>
From:   Qu Wenruo <quwenruo.btrfs@gmx.com>
In-Reply-To: <20220615132147.GA18252@lst.de>
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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 int=
o
>> 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