[PATCH] ASoC: qcom: q6apm-lpass-dais: Fix NULL pointer dereference if source graph failed

[Krzysztof Kozlowski <krzysztof.kozlowski@xxxxxxxxxx>]

If earlier opening of source graph fails (e.g. ADSP rejects due to
incorrect audioreach topology), the graph is closed and
"dai_data->graph[dai->id]" is assigned NULL.  Preparing the DAI for sink
graph continues though and next call to q6apm_lpass_dai_prepare()
receives dai_data->graph[dai->id]=NULL leading to NULL pointer
exception:

  qcom-apm gprsvc:service:2:1: Error (1) Processing 0x01001002 cmd
  qcom-apm gprsvc:service:2:1: DSP returned error[1001002] 1
  q6apm-lpass-dais 30000000.remoteproc:glink-edge:gpr:service@1:bedais: fail to start APM port 78
  q6apm-lpass-dais 30000000.remoteproc:glink-edge:gpr:service@1:bedais: ASoC: error at snd_soc_pcm_dai_prepare on TX_CODEC_DMA_TX_3: -22
  Unable to handle kernel NULL pointer dereference at virtual address 00000000000000a8
  ...
  Call trace:
   q6apm_graph_media_format_pcm+0x48/0x120 (P)
   q6apm_lpass_dai_prepare+0x110/0x1b4
   snd_soc_pcm_dai_prepare+0x74/0x108
   __soc_pcm_prepare+0x44/0x160
   dpcm_be_dai_prepare+0x124/0x1c0

Fixes: 30ad723b93ad ("ASoC: qdsp6: audioreach: add q6apm lpass dai support")
Cc: <stable@xxxxxxxxxxxxxxx>
Signed-off-by: Krzysztof Kozlowski <krzysztof.kozlowski@xxxxxxxxxx>
---
 sound/soc/qcom/qdsp6/q6apm-lpass-dais.c | 6 ++++++
 1 file changed, 6 insertions(+)

diff --git a/sound/soc/qcom/qdsp6/q6apm-lpass-dais.c b/sound/soc/qcom/qdsp6/q6apm-lpass-dais.c
index f90628d9b90e..7520e6f024c3 100644
--- a/sound/soc/qcom/qdsp6/q6apm-lpass-dais.c
+++ b/sound/soc/qcom/qdsp6/q6apm-lpass-dais.c
@@ -191,6 +191,12 @@ static int q6apm_lpass_dai_prepare(struct snd_pcm_substream *substream, struct s
 			return rc;
 		}
 		dai_data->graph[graph_id] = graph;
+	} else if (!dai_data->graph[dai->id]) {
+		/*
+		 * Loading source graph failed before, so abort loading the sink
+		 * as well.
+		 */
+		return -EINVAL;
 	}
 
 	cfg->direction = substream->stream;
-- 
2.48.1