linux-kernel - Re: [PATCH] sound/isa/sb/emu8000: Fix a use after free in snd_emu8000_create

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Date:   Mon, 26 Apr 2021 16:23:15 +0200
From:   Takashi Iwai <tiwai@...e.de>
To:     Lv Yunlong <lyl2019@...l.ustc.edu.cn>
Cc:     perex@...ex.cz, tiwai@...e.com, alsa-devel@...a-project.org,
        linux-kernel@...r.kernel.org
Subject: Re: [PATCH] sound/isa/sb/emu8000: Fix a use after free in snd_emu8000_create_mixer

On Mon, 26 Apr 2021 15:11:29 +0200,
Lv Yunlong wrote:
> 
> Our code analyzer reported a uaf.
> 
> In snd_emu8000_create_mixer, the callee snd_ctl_add(..,emu->controls[i])
> calls snd_ctl_add_replace(.., kcontrol,..). Inside snd_ctl_add_replace(),
> if error happens, kcontrol will be freed by snd_ctl_free_one(kcontrol).
> Then emu->controls[i] points to a freed memory, and the execution comes
> to __error branch of snd_emu8000_create_mixer. The freed emu->controls[i]
> is used in snd_ctl_remove(card, emu->controls[i]).
> 
> My patch set emu->controls[i] to NULL if snd_ctl_add() failed to avoid
> the uaf.
> 
> Signed-off-by: Lv Yunlong <lyl2019@...l.ustc.edu.cn>

Thanks, applied now.

The bug was hard to be seen due to the coding style, so we'd need a
cleanup, but it's a different story...


Takashi