Re: [PATCH] ALSA: usb-audio: Fix use-after-free in snd_usb_mixer_free()

[Takashi Iwai <tiwai@suse.de>]

On Tue, 20 Jan 2026 11:28:55 +0100,
Berk Cem Goksel wrote:
> 
> When snd_usb_create_mixer() fails, snd_usb_mixer_free() frees
> mixer->id_elems but the controls already added to the card still
> reference the freed memory. Later when snd_card_register() runs,
> the OSS mixer layer calls their callbacks and hits a use-after-free read.
> 
> Call trace:
>   get_ctl_value+0x63f/0x820 sound/usb/mixer.c:411
>   get_min_max_with_quirks.isra.0+0x240/0x1f40 sound/usb/mixer.c:1241
>   mixer_ctl_feature_info+0x26b/0x490 sound/usb/mixer.c:1381
>   snd_mixer_oss_build_test+0x174/0x3a0 sound/core/oss/mixer_oss.c:887
>   ...
>   snd_card_register+0x4ed/0x6d0 sound/core/init.c:923
>   usb_audio_probe+0x5ef/0x2a90 sound/usb/card.c:1025
> 
> Fix by calling snd_ctl_remove() for all mixer controls before freeing
> id_elems. We save the next pointer first because snd_ctl_remove()
> frees the current element.
> 
> Fixes: 6639b6c2367f ("[ALSA] usb-audio - add mixer control notifications")
> Cc: stable@vger.kernel.org
> Cc: Andrey Konovalov <andreyknvl@gmail.com>
> Signed-off-by: Berk Cem Goksel <berkcgoksel@gmail.com>

Thanks, applied now.


Takashi