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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>
From:   Yu Kuai <yukuai1@huaweicloud.com>
Message-ID: <eca5a778-6795-fc03-7ae0-fe06f514af85@huaweicloud.com>
Date:   Wed, 12 Jul 2023 18:04:57 +0800
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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().

Thanks,
Kuai