Re: [PATCH] ALSA: line6: Improve poor error handling in line6_init_cap_control

[Takashi Iwai <tiwai@suse.de>]

On Mon, 24 May 2021 19:36:44 +0200,
Hyeonggon Yoo wrote:
> 
> line6_init_cap_control doesn't free resources properly when allocations
> like kmalloc, usb_alloc_urb fails. It can cause memory leak when some
> allocations succeed, and then an error occurs.
> 
> This patch makes line6_init_cap_control to properly free the resources,
> freeing previously allocated resources when there's an error.
> 
> Signed-off-by: Hyeonggon Yoo <42.hyeyoo@gmail.com>
> ---
>  sound/usb/line6/driver.c | 36 +++++++++++++++++++++++++++---------
>  1 file changed, 27 insertions(+), 9 deletions(-)
> 
> diff --git a/sound/usb/line6/driver.c b/sound/usb/line6/driver.c
> index 9602929b7de9..6991cb855023 100644
> --- a/sound/usb/line6/driver.c
> +++ b/sound/usb/line6/driver.c
> @@ -688,34 +688,52 @@ static int line6_init_cap_control(struct usb_line6 *line6)
>  
>  	/* initialize USB buffers: */
>  	line6->buffer_listen = kmalloc(LINE6_BUFSIZE_LISTEN, GFP_KERNEL);
> -	if (!line6->buffer_listen)
> -		return -ENOMEM;
> +	if (!line6->buffer_listen) {
> +		ret = -ENOMEM;
> +		goto fail_ret;
> +	}
>  
>  	line6->urb_listen = usb_alloc_urb(0, GFP_KERNEL);
> -	if (!line6->urb_listen)
> -		return -ENOMEM;
> +	if (!line6->urb_listen) {
> +		ret = -ENOMEM;
> +		goto fail1;
> +	}
>  
>  	if (line6->properties->capabilities & LINE6_CAP_CONTROL_MIDI) {
>  		line6->buffer_message = kmalloc(LINE6_MIDI_MESSAGE_MAXLEN, GFP_KERNEL);
> -		if (!line6->buffer_message)
> -			return -ENOMEM;
> +		if (!line6->buffer_message) {
> +			ret = -ENOMEM;
> +			goto fail2;
> +		}
>  
>  		ret = line6_init_midi(line6);
>  		if (ret < 0)
> -			return ret;
> +			goto fail3;
>  	} else {
>  		ret = line6_hwdep_init(line6);
>  		if (ret < 0)
> -			return ret;
> +			goto fail2;
>  	}
>  
>  	ret = line6_start_listen(line6);
>  	if (ret < 0) {
>  		dev_err(line6->ifcdev, "cannot start listening: %d\n", ret);
> -		return ret;
> +		if (line6->properties->capabilities & LINE6_CAP_CONTROL_MIDI)
> +			goto fail3;
> +		else
> +			goto fail2;
>  	}
>  
>  	return 0;
> +
> +fail3:
> +	kfree(line6->buffer_message);
> +fail2:
> +	usb_free_urb(line6->urb_listen);
> +fail1:
> +	kfree(line6->buffer_listen);
> +fail_ret:
> +	return ret;
>  }

Those resources are freed in the common destructor of the card
instance, line6_destruct(), at disconnect callback, so it's redundant
to release them here; even worse, since you haven't re-initialize with
NULL, this change would lead to double-free.


thanks,

Takashi