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

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Date: Sat, 18 May 2024 14:58:08 +0900
From: Yunseong Kim <yskelg@...il.com>
To: Bjorn Helgaas <helgaas@...nel.org>, Takashi Iwai <tiwai@...e.de>
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 5/18/24 2:44 오전, Bjorn Helgaas wrote:
> 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.

Thank you Bjorn for your detailed advice. I will take them to heart and
work on them in the future.

Warm Regards,
Yunseong Kim

>>> ---
>>>  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
>>>