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

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Date: Fri, 17 May 2024 12:44:26 -0500
From: Bjorn Helgaas <helgaas@...nel.org>
To: Takashi Iwai <tiwai@...e.de>
Cc: yskelg@...il.com, 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 Fri, May 17, 2024 at 10:32:13AM +0200, Takashi Iwai wrote:
> 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.

I stand corrected, sorry that I missed that!

That said, it seems unreasonably hard to verify this path to
snd_line6_midi_free().

Sorry for misleading you, Yunseong.

> > ---
> >  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
> >