ASoC: Fix use-after-free at card unregistration

commit 4efda5f2 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@free.fr>
Signed-off-by: Takashi Iwai <tiwai@suse.de>
Signed-off-by: Mark Brown <broonie@kernel.org>
[bwh: Backported to 3.16: adjust context]
Signed-off-by: Ben Hutchings <ben@decadent.org.uk>

sound/soc/soc-core.c

@@ -2014,6 +2014,9 @@ static int soc_cleanup_card_resources(struct snd_soc_card *card)
 	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 */
 	soc_remove_dai_links(card);
 
@@ -2025,9 +2028,7 @@ static int soc_cleanup_card_resources(struct snd_soc_card *card)
 
 	snd_soc_dapm_free(&card->dapm);
 
-	snd_card_free(card->snd_card);
 	return 0;
-
 }
 
 /* removes a socdev */