linux-kernel - Re: [PATCH -nect RFC v2 0/2] block: fix uaf in bd_link_disk

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Date:   Mon, 31 Oct 2022 09:08:11 +0800
From:   Yu Kuai <yukuai1@...weicloud.com>
To:     Christoph Hellwig <hch@....de>, Yu Kuai <yukuai1@...weicloud.com>
Cc:     axboe@...nel.dk, willy@...radead.org, kch@...dia.com,
        martin.petersen@...cle.com, johannes.thumshirn@....com,
        ming.lei@...hat.com, linux-block@...r.kernel.org,
        linux-kernel@...r.kernel.org, yi.zhang@...wei.com,
        "yukuai (C)" <yukuai3@...wei.com>
Subject: Re: [PATCH -nect RFC v2 0/2] block: fix uaf in bd_link_disk_holder()

Hi, Christoph

在 2022/10/30 23:30, Christoph Hellwig 写道:
> On Fri, Oct 21, 2022 at 11:15:34AM +0800, Yu Kuai wrote:
>> Hi,
>>
>> 在 2022/10/21 0:47, Christoph Hellwig 写道:
>>> As mentioned before I don't think we should make this even more
>>> crufty in the block layer.  See the series I just sent to move it int
>>> dm.
>>
>> It seems we had some misunderstanding, the problem I tried to fix here
>> should not just related to dm, but all the caller of
>> bd_link_disk_holder().
> 
> As far as I can tell the problem was just that patch 1 in my series blows
> away the bd_holder_dir pointer in part0 on del_gendisk.  Each holder
> actually holds a reference to the kobject, so the memory for it is
> still valid, it's just that the pointer got cleared.  I'll send a v2
> in a bit.

This is not the real case. In bd_link_disk_hoder(), bd_hodler_dir is
accessed first by add_symlink(), and then reference is grabed later.
The reference should be grabed before bd_holder_dir is accessed, like
what I try to do in patch 2.

Thanks,
Kuai
> 
> .
>