linux-kernel - Re: [PATCH] ALSA: usb-audio: fix a memory leak bug

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Date:   Tue, 06 Aug 2019 08:40:23 +0200
From:   Takashi Iwai <tiwai@...e.de>
To:     Wenwen Wang <wenwen@...uga.edu>
Cc:     "moderated list:SOUND" <alsa-devel@...a-project.org>,
        Thomas Gleixner <tglx@...utronix.de>,
        Greg Kroah-Hartman <gregkh@...uxfoundation.org>,
        Kate Stewart <kstewart@...uxfoundation.org>,
        Allison Randal <allison@...utok.net>,
        Jaroslav Kysela <perex@...ex.cz>,
        Richard Fontana <rfontana@...hat.com>,
        Takashi Iwai <tiwai@...e.com>,
        open list <linux-kernel@...r.kernel.org>
Subject: Re: [PATCH] ALSA: usb-audio: fix a memory leak bug

On Tue, 06 Aug 2019 08:13:06 +0200,
Wenwen Wang wrote:
> 
> In add_new_ctl(), a mixer element structure is allocated through kzalloc()
> and the pointer is saved to 'elem'. Later on, a new alsa control element is
> created and added to this structure. In case the add process fails, i.e.,
> the return value of snd_usb_mixer_add_control() is less than 0, the
> allocated structure is not freed, leading to a memory leak.
> 
> To fix the above issue, free 'elem' before returning the error.
> 
> Signed-off-by: Wenwen Wang <wenwen@...uga.edu>

It's a false-positive.  snd_ctl_add() behaves differently from others,
it releases the given kctl at the error.  And in this case, elem
already gets freed by kctl->private_free callback.


thanks,

Takashi