linux-kernel - Re: [PATCH] line6: add midibuf init failure handling in line6_init

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Date: Fri, 17 May 2024 10:32:13 +0200
From: Takashi Iwai <tiwai@...e.de>
To: yskelg@...il.com
Cc: Jaroslav Kysela <perex@...ex.cz>,
	Takashi Iwai <tiwai@...e.com>,
	skhan@...uxfoundation.org,
	linux-kernel-mentees@...ts.linuxfoundation.org,
	Austin Kim <austindh.kim@...il.com>,
	shjy180909@...il.com,
	linux-sound@...r.kernel.org,
	linux-kernel@...r.kernel.org
Subject: Re: [PATCH] line6: add midibuf init failure handling in line6_init_midi()

On Thu, 16 May 2024 19:47:38 +0200,
yskelg@...il.com wrote:
> 
> From: Yunseong Kim <yskelg@...il.com>
> 
> This patch fixes potential memory allocation failures in the
> line6_midibuf_init(). If either midibuf_in, midibuf_out allocation
> line6_midibuf_init call failed, the allocated memory for line6midi
> might have been leaked.
> 
> This patch introduces an error handling label and uses goto to jump there
> in case of allocation failures. A kfree call is added to release any
> partially allocated memory before returning the error code.
> 
> Signed-off-by: Yunseong Kim <yskelg@...il.com>

The allocated object is already freed by snd_line6_midi_free() that is
called via rawmidi private_free at its destruction.  So your change
would lead to a double-free.


thanks,

Takashi

> ---
>  sound/usb/line6/midi.c | 9 +++++++--
>  1 file changed, 7 insertions(+), 2 deletions(-)
> 
> diff --git a/sound/usb/line6/midi.c b/sound/usb/line6/midi.c
> index 0838632c788e..abcf58f46673 100644
> --- a/sound/usb/line6/midi.c
> +++ b/sound/usb/line6/midi.c
> @@ -283,13 +283,18 @@ int line6_init_midi(struct usb_line6 *line6)
>  
>  	err = line6_midibuf_init(&line6midi->midibuf_in, MIDI_BUFFER_SIZE, 0);
>  	if (err < 0)
> -		return err;
> +		goto error;
>  
>  	err = line6_midibuf_init(&line6midi->midibuf_out, MIDI_BUFFER_SIZE, 1);
>  	if (err < 0)
> -		return err;
> +		goto error;
>  
>  	line6->line6midi = line6midi;
>  	return 0;
> +
> +error:
> +	kfree(line6midi);
> +	return err;
> +
>  }
>  EXPORT_SYMBOL_GPL(line6_init_midi);
> -- 
> 2.34.1
>