Received-SPF: pass (google.com: domain of linux-kernel-owner@vger.kernel.org designates 2620:137:e000::1:20 as permitted sender) client-ip=2620:137:e000::1:20;
Message-ID: <b19b4c51-c769-84f9-7eae-b555ae51d692@veeam.com>
Date:   Mon, 17 Jul 2023 19:39:55 +0200
MIME-Version: 1.0
User-Agent: Mozilla/5.0 (X11; Linux x86_64; rv:102.0) Gecko/20100101
 Thunderbird/102.12.0
Subject: Re: [PATCH v5 02/11] block: Block Device Filtering Mechanism
Content-Language: en-US
To:     Yu Kuai <yukuai1@huaweicloud.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>
 <2ab36e73-a612-76a8-9c20-f5e11c67bcc3@huaweicloud.com>
From:   Sergei Shtepa <sergei.shtepa@veeam.com>
In-Reply-To: <2ab36e73-a612-76a8-9c20-f5e11c67bcc3@huaweicloud.com>
Content-Type: text/plain; charset="UTF-8"
Content-Transfer-Encoding: 8bit
Precedence: bulk

Hi.

On 7/12/23 14:34, Yu Kuai wrote:
> Subject:
> Re: [PATCH v5 02/11] block: Block Device Filtering Mechanism
> From:
> Yu Kuai <yukuai1@huaweicloud.com>
> Date:
> 7/12/23, 14:34
> 
> 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>
> 
> 
> 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.
> 

Yes, it looks like if two threads execute the blkfilter_detach() function,
then a problem is possible. The blk_mq_freeze_queue() function does not
block threads.
But for this, it is necessary that the IOCTL for the block device and
its removal are performed simultaneously. Is this possible?

I suppose that using mutex bdev->bd_disk->open_mutex in
blkfilter_ioctl_attach(), blkfilter_ioctl_detach() and
blkfilter_ioctl_ctl() can fix the problem. What do you think?


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