linux-kernel - [PATCH 4.9 104/119] ASoC: Fix use-after-free at card unregistration

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Message-Id: <20170612152603.951891769@linuxfoundation.org>
Date:   Mon, 12 Jun 2017 17:26:06 +0200
From:   Greg Kroah-Hartman <gregkh@...uxfoundation.org>
To:     linux-kernel@...r.kernel.org
Cc:     Greg Kroah-Hartman <gregkh@...uxfoundation.org>,
        stable@...r.kernel.org, Takashi Iwai <tiwai@...e.de>,
        Mark Brown <broonie@...nel.org>
Subject: [PATCH 4.9 104/119] ASoC: Fix use-after-free at card unregistration

4.9-stable review patch.  If anyone has any objections, please let me know.

------------------

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

commit 4efda5f2130da033aeedc5b3205569893b910de2 upstream.

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>
Signed-off-by: Takashi Iwai <tiwai@...e.de>
Signed-off-by: Mark Brown <broonie@...nel.org>
Signed-off-by: Greg Kroah-Hartman <gregkh@...uxfoundation.org>

---
 sound/soc/soc-core.c |    5 +++--
 1 file changed, 3 insertions(+), 2 deletions(-)

--- a/sound/soc/soc-core.c
+++ b/sound/soc/soc-core.c
@@ -2076,6 +2076,9 @@ static int soc_cleanup_card_resources(st
 	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);
@@ -2090,9 +2093,7 @@ static int soc_cleanup_card_resources(st
 	if (card->remove)
 		card->remove(card);
 
-	snd_card_free(card->snd_card);
 	return 0;
-
 }
 
 /* removes a socdev */