Re: WARNING in sysfs_remove_group

[Greg KH <gregkh@linuxfoundation.org>]

On Wed, May 02, 2018 at 11:11:59PM +0900, Tetsuo Handa wrote:
> syzbot has hit this bug for nearly 6000 times. Why not to fix this trivial one? ;-)
> 
> >From 626d33de1b70b11ecaf95a9f83f7644998e54cbb Mon Sep 17 00:00:00 2001
> From: Tetsuo Handa <penguin-kernel@I-love.SAKURA.ne.jp>
> Date: Wed, 2 May 2018 23:03:48 +0900
> Subject: [PATCH] loop: remember whether sysfs_create_group() succeeded
> 
> syzbot is hitting WARN() triggered by memory allocation fault
> injection [1] because loop module is calling sysfs_remove_group()
> when sysfs_create_group() failed.
> Fix this by remembering whether sysfs_create_group() succeeded.
> 
> [1] https://syzkaller.appspot.com/bug?id=3f86c0edf75c86d2633aeb9dd69eccc70bc7e90b
> 
> Signed-off-by: Tetsuo Handa <penguin-kernel@I-love.SAKURA.ne.jp>
> Reported-by: syzbot <syzbot+9f03168400f56df89dbc6f1751f4458fe739ff29@syzkaller.appspotmail.com>
> Cc: Jens Axboe <axboe@kernel.dk>
> ---
>  drivers/block/loop.c | 11 ++++++-----
>  drivers/block/loop.h |  1 +
>  2 files changed, 7 insertions(+), 5 deletions(-)
> 
> diff --git a/drivers/block/loop.c b/drivers/block/loop.c
> index 5d4e316..1d758d8 100644
> --- a/drivers/block/loop.c
> +++ b/drivers/block/loop.c
> @@ -809,16 +809,17 @@ static ssize_t loop_attr_dio_show(struct loop_device *lo, char *buf)
>  	.attrs= loop_attrs,
>  };
>  
> -static int loop_sysfs_init(struct loop_device *lo)
> +static void loop_sysfs_init(struct loop_device *lo)
>  {
> -	return sysfs_create_group(&disk_to_dev(lo->lo_disk)->kobj,
> -				  &loop_attribute_group);
> +	lo->sysfs_ready = !sysfs_create_group(&disk_to_dev(lo->lo_disk)->kobj,
> +					      &loop_attribute_group);
>  }
>  
>  static void loop_sysfs_exit(struct loop_device *lo)
>  {
> -	sysfs_remove_group(&disk_to_dev(lo->lo_disk)->kobj,
> -			   &loop_attribute_group);
> +	if (lo->sysfs_ready)
> +		sysfs_remove_group(&disk_to_dev(lo->lo_disk)->kobj,
> +				   &loop_attribute_group);
>  }
>  
>  static void loop_config_discard(struct loop_device *lo)
> diff --git a/drivers/block/loop.h b/drivers/block/loop.h
> index b78de98..73c801f 100644
> --- a/drivers/block/loop.h
> +++ b/drivers/block/loop.h
> @@ -58,6 +58,7 @@ struct loop_device {
>  	struct kthread_worker	worker;
>  	struct task_struct	*worker_task;
>  	bool			use_dio;
> +	bool			sysfs_ready;
>  
>  	struct request_queue	*lo_queue;
>  	struct blk_mq_tag_set	tag_set;
> -- 
> 1.8.3.1
> 

Reviewed-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>