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From:   Greg Kroah-Hartman <gregkh@linuxfoundation.org>
To:     linux-kernel@vger.kernel.org
Cc:     Greg Kroah-Hartman <gregkh@linuxfoundation.org>,
        stable@vger.kernel.org, Lv Yunlong <lyl2019@mail.ustc.edu.cn>,
        Takashi Iwai <tiwai@suse.de>
Subject: [PATCH 4.19 074/425] ALSA: emu8000: Fix a use after free in snd_emu8000_create_mixer
Date:   Thu, 20 May 2021 11:17:23 +0200
Message-Id: <20210520092133.883131794@linuxfoundation.org>
In-Reply-To: <20210520092131.308959589@linuxfoundation.org>
References: <20210520092131.308959589@linuxfoundation.org>
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From: Lv Yunlong <lyl2019@mail.ustc.edu.cn>

commit 1c98f574403dbcf2eb832d5535a10d967333ef2d upstream.

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@mail.ustc.edu.cn>
Cc: <stable@vger.kernel.org>
Link: https://lore.kernel.org/r/20210426131129.4796-1-lyl2019@mail.ustc.edu.cn
Signed-off-by: Takashi Iwai <tiwai@suse.de>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>
---
 sound/isa/sb/emu8000.c |    4 +++-
 1 file changed, 3 insertions(+), 1 deletion(-)

--- a/sound/isa/sb/emu8000.c
+++ b/sound/isa/sb/emu8000.c
@@ -1042,8 +1042,10 @@ snd_emu8000_create_mixer(struct snd_card
 
 	memset(emu->controls, 0, sizeof(emu->controls));
 	for (i = 0; i < EMU8000_NUM_CONTROLS; i++) {
-		if ((err = snd_ctl_add(card, emu->controls[i] = snd_ctl_new1(mixer_defs[i], emu))) < 0)
+		if ((err = snd_ctl_add(card, emu->controls[i] = snd_ctl_new1(mixer_defs[i], emu))) < 0) {
+			emu->controls[i] = NULL;
 			goto __error;
+		}
 	}
 	return 0;