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Subject: Re: [PATCH v5 02/11] block: Block Device Filtering Mechanism
To:     Yu Kuai <yukuai1@huaweicloud.com>,
        Sergei Shtepa <sergei.shtepa@veeam.com>, axboe@kernel.dk,
        hch@infradead.org, corbet@lwn.net, snitzer@kernel.org
Cc:     viro@zeniv.linux.org.uk, brauner@kernel.org, dchinner@redhat.com,
        willy@infradead.org, dlemoal@kernel.org, linux@weissschuh.net,
        jack@suse.cz, ming.lei@redhat.com, linux-block@vger.kernel.org,
        linux-doc@vger.kernel.org, linux-kernel@vger.kernel.org,
        linux-fsdevel@vger.kernel.org,
        Donald Buczek <buczek@molgen.mpg.de>,
        "yukuai (C)" <yukuai3@huawei.com>
References: <20230612135228.10702-1-sergei.shtepa@veeam.com>
 <20230612135228.10702-3-sergei.shtepa@veeam.com>
 <f935840e-12a7-c37b-183c-27e2d83990ea@huaweicloud.com>
 <eca5a778-6795-fc03-7ae0-fe06f514af85@huaweicloud.com>
From:   Yu Kuai <yukuai1@huaweicloud.com>
Message-ID: <2ab36e73-a612-76a8-9c20-f5e11c67bcc3@huaweicloud.com>
Date:   Wed, 12 Jul 2023 20:34:57 +0800
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Hi,

在 2023/07/12 18:04, Yu Kuai 写道:
> Hi,
> 
> 在 2023/07/11 10:02, Yu Kuai 写道:
> 
>>> +static bool submit_bio_filter(struct bio *bio)
>>> +{
>>> +    if (bio_flagged(bio, BIO_FILTERED))
>>> +        return false;
>>> +
>>> +    bio_set_flag(bio, BIO_FILTERED);
>>> +    return bio->bi_bdev->bd_filter->ops->submit_bio(bio);
>>> +}
>>> +
>>>   static void __submit_bio(struct bio *bio)
>>>   {
>>> +    /*
>>> +     * If there is a filter driver attached, check if the BIO needs 
>>> to go to
>>> +     * the filter driver first, which can then pass on the bio or 
>>> consume it.
>>> +     */
>>> +    if (bio->bi_bdev->bd_filter && submit_bio_filter(bio))
>>> +        return;
>>> +
>>>       if (unlikely(!blk_crypto_bio_prep(&bio)))
>>>           return;
> 
> ...
> 
>>> +static void __blkfilter_detach(struct block_device *bdev)
>>> +{
>>> +    struct blkfilter *flt = bdev->bd_filter;
>>> +    const struct blkfilter_operations *ops = flt->ops;
>>> +
>>> +    bdev->bd_filter = NULL;
>>> +    ops->detach(flt);
>>> +    module_put(ops->owner);
>>> +}
>>> +
>>> +void blkfilter_detach(struct block_device *bdev)
>>> +{
>>> +    if (bdev->bd_filter) {
>>> +        blk_mq_freeze_queue(bdev->bd_queue);
> 
> And this is not sate as well, for bio-based device, q_usage_counter is
> not grabbed while submit_bio_filter() is called, hence there is a risk
> of uaf from submit_bio_filter().

And there is another question, can blkfilter_detach() from
del_gendisk/delete_partiton and ioctl concurrent? I think it's a
problem.

Thanks,
Kuai
> 
> Thanks,
> Kuai
> 
> .
>