ASoC: dapm: Move dai_link widgets to runtime to fix use after free

The newly added CODEC to CODEC DAI link widget pointers in
snd_soc_dai_link are better placed in snd_soc_pcm_runtime.
snd_soc_dai_link is really intended for static configuration of
the DAI, and the runtime for dynamic data.  The snd_soc_dai_link
structures are not destroyed if the card is unbound. The widgets
are cleared up on unbind, however if the card is rebound as the
snd_soc_dai_link structures are reused these pointers will be left at
their old values, causing access to freed memory.

Fixes: 595571c ("ASoC: dapm: Fix regression introducing multiple copies of DAI widgets")
Signed-off-by: Charles Keepax <ckeepax@opensource.cirrus.com>
Link: https://lore.kernel.org/r/20200526161930.30759-1-ckeepax@opensource.cirrus.com
Signed-off-by: Mark Brown <broonie@kernel.org>

Author: charleskeepax

include/sound/soc.h

@@ -790,9 +790,6 @@ struct snd_soc_dai_link {
 	const struct snd_soc_pcm_stream *params;
 	unsigned int num_params;
 
-	struct snd_soc_dapm_widget *playback_widget;
-	struct snd_soc_dapm_widget *capture_widget;
-
 	unsigned int dai_fmt;           /* format to set on init */
 
 	enum snd_soc_dpcm_trigger trigger[2]; /* trigger type for DPCM */
@@ -1156,6 +1153,9 @@ struct snd_soc_pcm_runtime {
 	struct snd_soc_dai **cpu_dais;
 	unsigned int num_cpus;
 
+	struct snd_soc_dapm_widget *playback_widget;
+	struct snd_soc_dapm_widget *capture_widget;
+
 	struct delayed_work delayed_work;
 	void (*close_delayed_work_func)(struct snd_soc_pcm_runtime *rtd);
 #ifdef CONFIG_DEBUG_FS

sound/soc/soc-dapm.c

@@ -4340,16 +4340,16 @@ static void dapm_connect_dai_pair(struct snd_soc_card *card,
 	codec = codec_dai->playback_widget;
 
 	if (playback_cpu && codec) {
-		if (dai_link->params && !dai_link->playback_widget) {
+		if (dai_link->params && !rtd->playback_widget) {
 			substream = streams[SNDRV_PCM_STREAM_PLAYBACK].substream;
 			dai = snd_soc_dapm_new_dai(card, substream, "playback");
 			if (IS_ERR(dai))
 				goto capture;
-			dai_link->playback_widget = dai;
+			rtd->playback_widget = dai;
 		}
 
 		dapm_connect_dai_routes(&card->dapm, cpu_dai, playback_cpu,
-					dai_link->playback_widget,
+					rtd->playback_widget,
 					codec_dai, codec);
 	}
 
@@ -4358,16 +4358,16 @@ static void dapm_connect_dai_pair(struct snd_soc_card *card,
 	codec = codec_dai->capture_widget;
 
 	if (codec && capture_cpu) {
-		if (dai_link->params && !dai_link->capture_widget) {
+		if (dai_link->params && !rtd->capture_widget) {
 			substream = streams[SNDRV_PCM_STREAM_CAPTURE].substream;
 			dai = snd_soc_dapm_new_dai(card, substream, "capture");
 			if (IS_ERR(dai))
 				return;
-			dai_link->capture_widget = dai;
+			rtd->capture_widget = dai;
 		}
 
 		dapm_connect_dai_routes(&card->dapm, codec_dai, codec,
-					dai_link->capture_widget,
+					rtd->capture_widget,
 					cpu_dai, capture_cpu);
 	}
 }