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Date:   Mon, 17 Jul 2023 18:22:46 +0200
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Subject: Re: [PATCH v5 02/11] block: Block Device Filtering Mechanism
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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>
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 <f935840e-12a7-c37b-183c-27e2d83990ea@huaweicloud.com>
 <eca5a778-6795-fc03-7ae0-fe06f514af85@huaweicloud.com>
From:   Sergei Shtepa <sergei.shtepa@veeam.com>
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On 7/12/23 12:04, Yu Kuai wrote:
> Subject:
> Re: [PATCH v5 02/11] block: Block Device Filtering Mechanism
> From:
> Yu Kuai <yukuai1@huaweicloud.com>
> Date:
> 7/12/23, 12:04
> 
> 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 2023/07/11 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
> 

Hi Kuai.

Indeed, the filter call is performed before calling bio_queue_enter().
I must admit, you are very attentive. 

I didn't keep track of the change in the position of the
bio_queue_enter() function deeper on the stack.

I think I need to add a check for q_usage_counter, for the debug build.
So that I don't miss it in the future.