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

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Date:   Mon, 26 Apr 2021 06:11:29 -0700
From:   Lv Yunlong <lyl2019@...l.ustc.edu.cn>
To:     perex@...ex.cz, tiwai@...e.com
Cc:     alsa-devel@...a-project.org, linux-kernel@...r.kernel.org,
        Lv Yunlong <lyl2019@...l.ustc.edu.cn>
Subject: [PATCH] sound/isa/sb/emu8000: Fix a use after free in snd_emu8000_create_mixer

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>
---
 sound/isa/sb/emu8000.c | 4 +++-
 1 file changed, 3 insertions(+), 1 deletion(-)

diff --git a/sound/isa/sb/emu8000.c b/sound/isa/sb/emu8000.c
index 0aa545ac6e60..1c90421a88dc 100644
--- a/sound/isa/sb/emu8000.c
+++ b/sound/isa/sb/emu8000.c
@@ -1029,8 +1029,10 @@ snd_emu8000_create_mixer(struct snd_card *card, struct snd_emu8000 *emu)

 	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;

-- 
2.25.1