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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 5.4 127/184] ALSA: sb: Fix two use after free in snd_sb_qsound_build
Date:   Mon, 10 May 2021 12:20:21 +0200
Message-Id: <20210510101954.334013342@linuxfoundation.org>
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From: Lv Yunlong <lyl2019@mail.ustc.edu.cn>

commit 4fb44dd2c1dda18606348acdfdb97e8759dde9df upstream.

In snd_sb_qsound_build, snd_ctl_add(..,p->qsound_switch...) and
snd_ctl_add(..,p->qsound_space..) are called. But the second
arguments of snd_ctl_add() could be freed via snd_ctl_add_replace()
->snd_ctl_free_one(). After the error code is returned,
snd_sb_qsound_destroy(p) is called in __error branch.

But in snd_sb_qsound_destroy(), the freed p->qsound_switch and
p->qsound_space are still used by snd_ctl_remove().

My patch set p->qsound_switch and p->qsound_space to NULL if
snd_ctl_add() failed to avoid the uaf bugs. But these codes need
to further be improved with the code style.

Signed-off-by: Lv Yunlong <lyl2019@mail.ustc.edu.cn>
Cc: <stable@vger.kernel.org>
Link: https://lore.kernel.org/r/20210426145541.8070-1-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/sb16_csp.c |    8 ++++++--
 1 file changed, 6 insertions(+), 2 deletions(-)

--- a/sound/isa/sb/sb16_csp.c
+++ b/sound/isa/sb/sb16_csp.c
@@ -1045,10 +1045,14 @@ static int snd_sb_qsound_build(struct sn
 
 	spin_lock_init(&p->q_lock);
 
-	if ((err = snd_ctl_add(card, p->qsound_switch = snd_ctl_new1(&snd_sb_qsound_switch, p))) < 0)
+	if ((err = snd_ctl_add(card, p->qsound_switch = snd_ctl_new1(&snd_sb_qsound_switch, p))) < 0) {
+		p->qsound_switch = NULL;
 		goto __error;
-	if ((err = snd_ctl_add(card, p->qsound_space = snd_ctl_new1(&snd_sb_qsound_space, p))) < 0)
+	}
+	if ((err = snd_ctl_add(card, p->qsound_space = snd_ctl_new1(&snd_sb_qsound_space, p))) < 0) {
+		p->qsound_space = NULL;
 		goto __error;
+	}
 
 	return 0;