linux-kernel - [PATCH v2 12/12] ASoC: Fix use-after-free at card unregistration

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Date:   Mon, 19 Jun 2017 09:27:09 +0200
From:   Robert Jarzmik <robert.jarzmik@...e.fr>
To:     Dmitry Torokhov <dmitry.torokhov@...il.com>,
        Lee Jones <lee.jones@...aro.org>,
        Jaroslav Kysela <perex@...ex.cz>,
        Takashi Iwai <tiwai@...e.com>, Daniel Mack <daniel@...que.org>,
        Haojian Zhuang <haojian.zhuang@...il.com>,
        Robert Jarzmik <robert.jarzmik@...e.fr>,
        Liam Girdwood <lgirdwood@...il.com>,
        Mark Brown <broonie@...nel.org>,
        Lars-Peter Clausen <lars@...afoo.de>,
        Charles Keepax <ckeepax@...nsource.wolfsonmicro.com>
Cc:     linux-kernel@...r.kernel.org, linux-input@...r.kernel.org,
        patches@...nsource.wolfsonmicro.com, alsa-devel@...a-project.org,
        linux-arm-kernel@...ts.infradead.org, Takashi Iwai <tiwai@...e.de>,
        <stable@...r.kernel.org>
Subject: [PATCH v2 12/12] ASoC: Fix use-after-free at card unregistration

From: Takashi Iwai <tiwai@...e.de>

soc_cleanup_card_resources() call snd_card_free() at the last of its
procedure.  This turned out to lead to a use-after-free.
PCM runtimes have been already removed via soc_remove_pcm_runtimes(),
while it's dereferenced later in soc_pcm_free() called via
snd_card_free().

The fix is simple: just move the snd_card_free() call to the beginning
of the whole procedure.  This also gives another benefit: it
guarantees that all operations have been shut down before actually
releasing the resources, which was racy until now.

Reported-and-tested-by: Robert Jarzmik <robert.jarzmik@...e.fr>
Cc: <stable@...r.kernel.org>
Signed-off-by: Takashi Iwai <tiwai@...e.de>
---
 sound/soc/soc-core.c | 5 +++--
 1 file changed, 3 insertions(+), 2 deletions(-)

diff --git a/sound/soc/soc-core.c b/sound/soc/soc-core.c
index 2722bb0c5573..98d60f471c5d 100644
--- a/sound/soc/soc-core.c
+++ b/sound/soc/soc-core.c
@@ -2286,6 +2286,9 @@ static int soc_cleanup_card_resources(struct snd_soc_card *card)
 	list_for_each_entry(rtd, &card->rtd_list, list)
 		flush_delayed_work(&rtd->delayed_work);
 
+	/* free the ALSA card at first; this syncs with pending operations */
+	snd_card_free(card->snd_card);
+
 	/* remove and free each DAI */
 	soc_remove_dai_links(card);
 	soc_remove_pcm_runtimes(card);
@@ -2300,9 +2303,7 @@ static int soc_cleanup_card_resources(struct snd_soc_card *card)
 	if (card->remove)
 		card->remove(card);
 
-	snd_card_free(card->snd_card);
 	return 0;
-
 }
 
 /* removes a socdev */
-- 
2.1.4