linux-kernel - Re: [PATCH v2] scsi: bsg: Fix device unregistration

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Date:   Mon, 13 Sep 2021 09:39:56 +0200
From:   Johan Hovold <johan@...nel.org>
To:     Zenghui Yu <yuzenghui@...wei.com>
Cc:     linux-scsi@...r.kernel.org, linux-block@...r.kernel.org,
        linux-kernel@...r.kernel.org, fujita.tomonori@....ntt.co.jp,
        axboe@...nel.dk, martin.petersen@...cle.com, hch@....de,
        gregkh@...uxfoundation.org, wanghaibin.wang@...wei.com
Subject: Re: [PATCH v2] scsi: bsg: Fix device unregistration

On Sat, Sep 11, 2021 at 06:53:06PM +0800, Zenghui Yu wrote:
> We use device_initialize() to take refcount for the device but forget to
> put_device() on device teardown, which ends up leaking private data of the
> driver core, dev_name(), etc. This is reported by kmemleak at boot time if
> we compile kernel with DEBUG_TEST_DRIVER_REMOVE.
> 
> Note that adding the missing put_device() is _not_ sufficient to fix device
> unregistration. As we don't provide the .release() method for device, which
> turned out to be typically wrong and will be complained loudly by the
> driver core.
> 
> Fix both of them.
> 
> Fixes: ead09dd3aed5 ("scsi: bsg: Simplify device registration")
> Signed-off-by: Zenghui Yu <yuzenghui@...wei.com>
> ---
> * From v1 [1]:
>   - As pointed out by Johan, fix UAF and double-free on error path ...

Looks good now:

Reviewed-by: Johan Hovold <johan@...nel.org>

>   - ... so I didn't collect Christoph and Greg's R-b tags (but thanks
>     for reviewing)
> 
> [1] https://lore.kernel.org/r/20210909034608.1435-1-yuzenghui@huawei.com
> 
>  block/bsg.c | 23 +++++++++++++++--------
>  1 file changed, 15 insertions(+), 8 deletions(-)
> 
> diff --git a/block/bsg.c b/block/bsg.c
> index 351095193788..882f56bff14f 100644
> --- a/block/bsg.c
> +++ b/block/bsg.c
> @@ -165,13 +165,20 @@ static const struct file_operations bsg_fops = {
>  	.llseek		=	default_llseek,
>  };
>  
> +static void bsg_device_release(struct device *dev)
> +{
> +	struct bsg_device *bd = container_of(dev, struct bsg_device, device);
> +
> +	ida_simple_remove(&bsg_minor_ida, MINOR(bd->device.devt));
> +	kfree(bd);
> +}
> +
>  void bsg_unregister_queue(struct bsg_device *bd)
>  {
>  	if (bd->queue->kobj.sd)
>  		sysfs_remove_link(&bd->queue->kobj, "bsg");
>  	cdev_device_del(&bd->cdev, &bd->device);
> -	ida_simple_remove(&bsg_minor_ida, MINOR(bd->device.devt));
> -	kfree(bd);
> +	put_device(&bd->device);
>  }
>  EXPORT_SYMBOL_GPL(bsg_unregister_queue);
>  
> @@ -193,11 +200,13 @@ struct bsg_device *bsg_register_queue(struct request_queue *q,
>  	if (ret < 0) {
>  		if (ret == -ENOSPC)
>  			dev_err(parent, "bsg: too many bsg devices\n");
> -		goto out_kfree;
> +		kfree(bd);
> +		return ERR_PTR(ret);
>  	}
>  	bd->device.devt = MKDEV(bsg_major, ret);
>  	bd->device.class = bsg_class;
>  	bd->device.parent = parent;
> +	bd->device.release = bsg_device_release;
>  	dev_set_name(&bd->device, "%s", name);
>  	device_initialize(&bd->device);
>  
> @@ -205,7 +214,7 @@ struct bsg_device *bsg_register_queue(struct request_queue *q,
>  	bd->cdev.owner = THIS_MODULE;
>  	ret = cdev_device_add(&bd->cdev, &bd->device);
>  	if (ret)
> -		goto out_ida_remove;
> +		goto out_put_device;
>  
>  	if (q->kobj.sd) {
>  		ret = sysfs_create_link(&q->kobj, &bd->device.kobj, "bsg");
> @@ -217,10 +226,8 @@ struct bsg_device *bsg_register_queue(struct request_queue *q,
>  
>  out_device_del:
>  	cdev_device_del(&bd->cdev, &bd->device);
> -out_ida_remove:
> -	ida_simple_remove(&bsg_minor_ida, MINOR(bd->device.devt));
> -out_kfree:
> -	kfree(bd);
> +out_put_device:
> +	put_device(&bd->device);
>  	return ERR_PTR(ret);
>  }
>  EXPORT_SYMBOL_GPL(bsg_register_queue);