linux-kernel - Re: [PATCH] loop: mask loop_control

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Date:   Thu, 18 Nov 2021 23:15:07 +0900
From:   Tetsuo Handa <penguin-kernel@...ove.SAKURA.ne.jp>
To:     wangyangbo <yangbonis@...oud.com>, axboe@...nel.dk
Cc:     linux-block@...r.kernel.org, linux-kernel@...r.kernel.org
Subject: Re: [PATCH] loop: mask loop_control_ioctl parameter only as minor

On 2021/11/18 11:36, wangyangbo wrote:
> @@ -2170,11 +2170,11 @@ static long loop_control_ioctl(struct file *file, unsigned int cmd,
>  {
>  	switch (cmd) {
>  	case LOOP_CTL_ADD:
> -		return loop_add(parm);
> +		return loop_add(MINOR(parm));

Better to return -EINVAL or something if out of minor range?

>  	case LOOP_CTL_REMOVE:
> -		return loop_control_remove(parm);
> +		return loop_control_remove(MINOR(parm));

This is bad, for this change makes

	if (idx < 0) {
		pr_warn("deleting an unspecified loop device is not supported.\n");
		return -EINVAL;
	}

dead code by masking the argument to 0-1048575 range.

>  	case LOOP_CTL_GET_FREE:
> -		return loop_control_get_free(parm);
> +		return loop_control_get_free(MINOR(parm));

This is pointless, for the passed argument is not used.
By the way, didn't someone already propose removal of this argument?

>  	default:
>  		return -ENOSYS;
>  	}
>