ALSA: hda: Fix possible null-ptr-deref when assigning a stream

[ Upstream commit f93dc90 ]

While AudioDSP drivers assign streams exclusively of HOST or LINK type,
nothing blocks a user to attempt to assign a COUPLED stream. As
supplied substream instance may be a stub, what is the case when
code-loading, such scenario ends with null-ptr-deref.

Signed-off-by: Cezary Rojewski <cezary.rojewski@intel.com>
Link: https://lore.kernel.org/r/20231006102857.749143-2-cezary.rojewski@intel.com
Signed-off-by: Takashi Iwai <tiwai@suse.de>
Signed-off-by: Sasha Levin <sashal@kernel.org>

sound/hda/hdac_stream.c

@@ -354,8 +354,10 @@ struct hdac_stream *snd_hdac_stream_assign(struct hdac_bus *bus,
 	struct hdac_stream *res = NULL;
 
 	/* make a non-zero unique key for the substream */
-	int key = (substream->pcm->device << 16) | (substream->number << 2) |
-		(substream->stream + 1);
+	int key = (substream->number << 2) | (substream->stream + 1);
+
+	if (substream->pcm)
+		key |= (substream->pcm->device << 16);
 
 	spin_lock_irq(&bus->reg_lock);
 	list_for_each_entry(azx_dev, &bus->stream_list, list) {