Re: [PATCH] ALSA: usb-audio: Fix memory leak in __snd_usbmidi_create

From: Clemens Ladisch
Date: Mon Oct 28 2019 - 12:48:04 EST

Navid Emamdoost wrote:
> On Mon, Oct 28, 2019 at 1:27 AM Takashi Iwai <tiwai@xxxxxxx> wrote:
>> On Sun, 27 Oct 2019 23:10:06 +0100,
>> Navid Emamdoost wrote:
>>> In the implementation of __snd_usbmidi_create() there is a memory leak
>>> caused by incorrect goto destination. Go to free_midi if
>>> snd_usbmidi_create_endpoints_midiman() or snd_usbmidi_create_endpoints()
>>> fail.
>> No, this will lead to double-free. After registering the rawmidi
>> interface at snd_usbmidi_create_rawmidi(), the common destructor will
>> be called via rawmidi private_free callback, and this will release the
>> all resources already.
> Now I can see how rawmidi private_free is set up to release the
> resources, but what concerns me is that at the moment of endpoint/port
> creation umidi is not yet added to the midi_list.
> In other words, what I see is that we still have just one local
> pointer to umidi if any of snd_usbmidi_create_endpoint* fail.

The snd_rawmidi device is automatically registered with the card, so the
line "rmidi->private_free = snd_usbmidi_rawmidi_free;" is the exact point
where the ownership of umidi changes. midi_list does not matter.