linux-kernel - Re: [PATCH v3] loop: drop caches if offset or block

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Date:   Tue, 8 Jan 2019 21:22:34 -0800
From:   Jaegeuk Kim <jaegeuk@...nel.org>
To:     Jens Axboe <axboe@...nel.dk>
Cc:     linux-kernel@...r.kernel.org, linux-block@...r.kernel.org
Subject: Re: [PATCH v3] loop: drop caches if offset or block_size are changed

Hi Jens,

May I ask whether this patch is acceptable?

Thanks,

On 12/18, Jaegeuk Kim wrote:
> If we don't drop caches used in old offset or block_size, we can get old data
> from new offset/block_size, which gives unexpected data to user.
> 
> For example, Martijn found a loopback bug in the below scenario.
> 1) LOOP_SET_FD loads first two pages on loop file
> 2) LOOP_SET_STATUS64 changes the offset on the loop file
> 3) mount is failed due to the cached pages having wrong superblock
> 
> Cc: Jens Axboe <axboe@...nel.dk>
> Cc: linux-block@...r.kernel.org
> Reported-by: Martijn Coenen <maco@...gle.com>
> Signed-off-by: Jaegeuk Kim <jaegeuk@...nel.org>
> ---
> v2 -> v3:
>  - avoid to submit IOs on frozen mq
> 
> Jens, how about this?
> 
> Thanks,
> 
>  drivers/block/loop.c | 29 +++++++++++++++++++++++++++--
>  1 file changed, 27 insertions(+), 2 deletions(-)
> 
> diff --git a/drivers/block/loop.c b/drivers/block/loop.c
> index cb0cc8685076..6b03121d62aa 100644
> --- a/drivers/block/loop.c
> +++ b/drivers/block/loop.c
> @@ -1126,6 +1126,12 @@ loop_set_status(struct loop_device *lo, const struct loop_info64 *info)
>  	if ((unsigned int) info->lo_encrypt_key_size > LO_KEY_SIZE)
>  		return -EINVAL;
>  
> +	if (lo->lo_offset != info->lo_offset ||
> +	    lo->lo_sizelimit != info->lo_sizelimit) {
> +		sync_blockdev(lo->lo_device);
> +		kill_bdev(lo->lo_device);
> +	}
> +
>  	/* I/O need to be drained during transfer transition */
>  	blk_mq_freeze_queue(lo->lo_queue);
>  
> @@ -1154,6 +1160,11 @@ loop_set_status(struct loop_device *lo, const struct loop_info64 *info)
>  
>  	if (lo->lo_offset != info->lo_offset ||
>  	    lo->lo_sizelimit != info->lo_sizelimit) {
> +		/* kill_bdev should have truncated all the pages */
> +		if (lo->lo_device->bd_inode->i_mapping->nrpages) {
> +			err = -EAGAIN;
> +			goto exit;
> +		}
>  		if (figure_loop_size(lo, info->lo_offset, info->lo_sizelimit)) {
>  			err = -EFBIG;
>  			goto exit;
> @@ -1375,22 +1386,36 @@ static int loop_set_dio(struct loop_device *lo, unsigned long arg)
>  
>  static int loop_set_block_size(struct loop_device *lo, unsigned long arg)
>  {
> +	int err = 0;
> +
>  	if (lo->lo_state != Lo_bound)
>  		return -ENXIO;
>  
>  	if (arg < 512 || arg > PAGE_SIZE || !is_power_of_2(arg))
>  		return -EINVAL;
>  
> +	if (lo->lo_queue->limits.logical_block_size != arg) {
> +		sync_blockdev(lo->lo_device);
> +		kill_bdev(lo->lo_device);
> +	}
> +
>  	blk_mq_freeze_queue(lo->lo_queue);
>  
> +	/* kill_bdev should have truncated all the pages */
> +	if (lo->lo_queue->limits.logical_block_size != arg &&
> +			lo->lo_device->bd_inode->i_mapping->nrpages) {
> +		err = -EAGAIN;
> +		goto out;
> +	}
> +
>  	blk_queue_logical_block_size(lo->lo_queue, arg);
>  	blk_queue_physical_block_size(lo->lo_queue, arg);
>  	blk_queue_io_min(lo->lo_queue, arg);
>  	loop_update_dio(lo);
> -
> +out:
>  	blk_mq_unfreeze_queue(lo->lo_queue);
>  
> -	return 0;
> +	return err;
>  }
>  
>  static int lo_ioctl(struct block_device *bdev, fmode_t mode,
> -- 
> 2.19.0.605.g01d371f741-goog