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Subject: Re: [PATCH -nect RFC v2 0/2] block: fix uaf in bd_link_disk_holder()
To:     Christoph Hellwig <hch@lst.de>, Yu Kuai <yukuai1@huaweicloud.com>
Cc:     axboe@kernel.dk, willy@infradead.org, kch@nvidia.com,
        martin.petersen@oracle.com, johannes.thumshirn@wdc.com,
        ming.lei@redhat.com, linux-block@vger.kernel.org,
        linux-kernel@vger.kernel.org, yi.zhang@huawei.com,
        "yukuai (C)" <yukuai3@huawei.com>
References: <20221020132049.3947415-1-yukuai3@huawei.com>
 <20221020164712.GA14773@lst.de>
 <0ad09045-1012-e86b-41f2-a88d02e8f1ed@huaweicloud.com>
 <20221030153040.GB9676@lst.de>
From:   Yu Kuai <yukuai1@huaweicloud.com>
Message-ID: <bdaec1ab-db1a-59d6-895e-1ac652a68950@huaweicloud.com>
Date:   Mon, 31 Oct 2022 09:08:11 +0800
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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
> 
> .
>