[PATCH v2] ALSA: hda: Do not unset preset when cleaning up codec

[Cezary Rojewski]

Several functions that take part in codec's initialization and removal
are re-used by ASoC codec drivers implementations. Drivers mimic the
behavior of hda_codec_driver_probe/remove() found in
sound/pci/hda/hda_bind.c with their component->probe/remove() instead.

One of the reasons for that is the expectation of
snd_hda_codec_device_new() to receive a valid pointer to an instance of
struct snd_card. This expectation can be met only once sound card
components probing commences.

As ASoC sound card may be unbound without codec device being actually
removed from the system, unsetting ->preset in
snd_hda_codec_cleanup_for_unbind() interferes with module unload -> load
scenario causing null-ptr-deref. Preset is assigned only once, during
device/driver matching whereas ASoC codec driver's module reloading may
occur several times throughout the lifetime of an audio stack.

Suggested-by: Takashi Iwai <tiwai at suse.com>
Signed-off-by: Cezary Rojewski <cezary.rojewski at intel.com>
---

Changes in v2:
- relocated the operation to routines found in hda_bind.c rather than
  just removing it from the cleanup function


This is a continuation of a discussion that begun in the middle of 2022
[1] and was part of a larger series addressing several HDAudio topics.

Single rmmod on ASoC's codec driver module is enough to cause a panic.
Given our results, no regression shows up with modprobe/rmmod on
snd_hda_intel side with this patch applied.

[1]: https://lore.kernel.org/alsa-devel/20220706120230.427296-2-cezary.rojewski@intel.com/

 sound/pci/hda/hda_bind.c  | 2 ++
 sound/pci/hda/hda_codec.c | 1 -
 2 files changed, 2 insertions(+), 1 deletion(-)

diff --git a/sound/pci/hda/hda_bind.c b/sound/pci/hda/hda_bind.c
index 1a868dd9dc4b..890c2f7c33fc 100644
--- a/sound/pci/hda/hda_bind.c
+++ b/sound/pci/hda/hda_bind.c
@@ -144,6 +144,7 @@ static int hda_codec_driver_probe(struct device *dev)
 
  error:
 	snd_hda_codec_cleanup_for_unbind(codec);
+	codec->preset = NULL;
 	return err;
 }
 
@@ -166,6 +167,7 @@ static int hda_codec_driver_remove(struct device *dev)
 	if (codec->patch_ops.free)
 		codec->patch_ops.free(codec);
 	snd_hda_codec_cleanup_for_unbind(codec);
+	codec->preset = NULL;
 	module_put(dev->driver->owner);
 	return 0;
 }
diff --git a/sound/pci/hda/hda_codec.c b/sound/pci/hda/hda_codec.c
index edd653ece70d..ac1cc7c5290e 100644
--- a/sound/pci/hda/hda_codec.c
+++ b/sound/pci/hda/hda_codec.c
@@ -795,7 +795,6 @@ void snd_hda_codec_cleanup_for_unbind(struct hda_codec *codec)
 	snd_array_free(&codec->cvt_setups);
 	snd_array_free(&codec->spdif_out);
 	snd_array_free(&codec->verbs);
-	codec->preset = NULL;
 	codec->follower_dig_outs = NULL;
 	codec->spdif_status_reset = 0;
 	snd_array_free(&codec->mixers);
-- 
2.25.1