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

From: Clemens Ladisch <clemens@ladisch.de>
To: Navid Emamdoost <navid.emamdoost@gmail.com>
Cc: Takashi Iwai <tiwai@suse.de>, Navid Emamdoost <emamd001@umn.edu>,
	Kangjie Lu <kjlu@umn.edu>, Stephen McCamant <smccaman@umn.edu>,
	Jaroslav Kysela <perex@perex.cz>,
	alsa-devel@alsa-project.org, LKML <linux-kernel@vger.kernel.org>
Subject: Re: [PATCH] ALSA: usb-audio: Fix memory leak in __snd_usbmidi_create
Date: Mon, 28 Oct 2019 17:38:56 +0100	[thread overview]
Message-ID: <d623a621-c62a-7ae9-958c-8709fb0c8c7d@ladisch.de> (raw)
In-Reply-To: <CAEkB2ESwKEQYQx75BnaHf4aUQHObx4jf0hreQx_KTeZ+QCjL4g@mail.gmail.com>

Navid Emamdoost wrote:
> On Mon, Oct 28, 2019 at 1:27 AM Takashi Iwai <tiwai@suse.de> 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.

Regards,
Clemens