[PATCH 3.16 088/233] ASoC: Fix use-after-free at card unregistration

From: Ben Hutchings
Date: Sat Sep 09 2017 - 19:21:00 EST

3.16.48-rc1 review patch. If anyone has any objections, please let me know.


From: Takashi Iwai <tiwai@xxxxxxx>

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

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@xxxxxxx>
Signed-off-by: Takashi Iwai <tiwai@xxxxxxx>
Signed-off-by: Mark Brown <broonie@xxxxxxxxxx>
[bwh: Backported to 3.16: adjust context]
Signed-off-by: Ben Hutchings <ben@xxxxxxxxxxxxxxx>
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
@@ -2014,6 +2014,9 @@ static int soc_cleanup_card_resources(st
for (i = 0; i < card->num_aux_devs; i++)
soc_remove_aux_dev(card, i);

+ /* free the ALSA card at first; this syncs with pending operations */
+ snd_card_free(card->snd_card);
/* remove and free each DAI */

@@ -2025,9 +2028,7 @@ static int soc_cleanup_card_resources(st


- snd_card_free(card->snd_card);
return 0;

/* removes a socdev */