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

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Date: Sat, 18 May 2024 02:10:44 +0900
From: Yunseong Kim <yskelg@...il.com>
To: Takashi Iwai <tiwai@...e.de>
Cc: Jaroslav Kysela <perex@...ex.cz>, skhan@...uxfoundation.org,
 Bjorn Helgaas <helgaas@...nel.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 5/17/24 5:32 오후, Takashi Iwai wrote:
> 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

Thanks for the review Takashi.

I have one question:

line6_midibuf_destroy() have no NULL check for the memory to free.

If line6midi->midibuf_in is in this->buf = NULL from
line6_midibuf_init() with memory allocation failed,
won't the free(NULL) when accessed by snd_line6_midi_free() to
line6_midibuf_destroy()?

In the first patch, I was making a misunderstanding
Now that you mention it, I can see where it's freeing!
It helped me a lot in analyzing the driver code.

Please let me know if I've misunderstood anything.

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
>>