Re: [PATCH v5 02/11] block: Block Device Filtering Mechanism

[Sergei Shtepa]

On 7/12/23 12:04, Yu Kuai wrote:
> Subject:
> Re: [PATCH v5 02/11] block: Block Device Filtering Mechanism
> From:
> Yu Kuai <yukuai1@xxxxxxxxxxxxxxx>
> Date:
> 7/12/23, 12:04
> 
> To:
> Yu Kuai <yukuai1@xxxxxxxxxxxxxxx>, Sergei Shtepa <sergei.shtepa@xxxxxxxxx>, axboe@xxxxxxxxx, hch@xxxxxxxxxxxxx, corbet@xxxxxxx, snitzer@xxxxxxxxxx
> CC:
> viro@xxxxxxxxxxxxxxxxxx, brauner@xxxxxxxxxx, dchinner@xxxxxxxxxx, willy@xxxxxxxxxxxxx, dlemoal@xxxxxxxxxx, linux@xxxxxxxxxxxxxx, jack@xxxxxxx, ming.lei@xxxxxxxxxx, linux-block@xxxxxxxxxxxxxxx, linux-doc@xxxxxxxxxxxxxxx, linux-kernel@xxxxxxxxxxxxxxx, linux-fsdevel@xxxxxxxxxxxxxxx, Donald Buczek <buczek@xxxxxxxxxxxxx>, "yukuai (C)" <yukuai3@xxxxxxxxxx>
> 
> 
> 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.