linux-kernel - Re: [PATCH] ALSA: usb-audio: Fix memleak in scarlett2_add_new

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Date:   Fri, 07 Aug 2020 10:04:41 +0200
From:   Takashi Iwai <tiwai@...e.de>
To:     Dinghao Liu <dinghao.liu@....edu.cn>
Cc:     kjlu@....edu, Jaroslav Kysela <perex@...ex.cz>,
        Takashi Iwai <tiwai@...e.com>, "Geoffrey D. Bennett" <g@...vu>,
        alsa-devel@...a-project.org, linux-kernel@...r.kernel.org
Subject: Re: [PATCH] ALSA: usb-audio: Fix memleak in scarlett2_add_new_ctl

On Fri, 07 Aug 2020 09:12:27 +0200,
Dinghao Liu wrote:
> 
> When snd_usb_mixer_add_control() fails, elem needs to be
> freed just like when snd_ctl_new1() fails. However, current
> code is returning directly and ends up leaking memory.

No, this would lead to double-free.  snd_ctl_add() shows a kind of
special behavior, it already releases the object at its error path.


thanks,

Takashi

> 
> Fixes: 9e4d5c1be21f0 ("ALSA: usb-audio: Scarlett Gen 2 mixer interface")
> Signed-off-by: Dinghao Liu <dinghao.liu@....edu.cn>
> ---
>  sound/usb/mixer_scarlett_gen2.c | 4 +++-
>  1 file changed, 3 insertions(+), 1 deletion(-)
> 
> diff --git a/sound/usb/mixer_scarlett_gen2.c b/sound/usb/mixer_scarlett_gen2.c
> index 74c00c905d24..4b2da0866cdc 100644
> --- a/sound/usb/mixer_scarlett_gen2.c
> +++ b/sound/usb/mixer_scarlett_gen2.c
> @@ -964,8 +964,10 @@ static int scarlett2_add_new_ctl(struct usb_mixer_interface *mixer,
>  	strlcpy(kctl->id.name, name, sizeof(kctl->id.name));
>  
>  	err = snd_usb_mixer_add_control(&elem->head, kctl);
> -	if (err < 0)
> +	if (err < 0) {
> +		kfree(elem);
>  		return err;
> +	}
>  
>  	if (kctl_return)
>  		*kctl_return = kctl;
> -- 
> 2.17.1
>