[PATCH] ALSA: x86: hdmi: fix chmap array missing terminator entry

[Peter Ujfalusi <peter.ujfalusi@linux.intel.com>]

had_build_channel_allocation_map() allocates a single struct
snd_pcm_chmap_elem via kzalloc() and stores it as
intelhaddata->chmap->chmap. struct snd_pcm_chmap.chmap is expected to
be a zero-terminated array (see snd_pcm_std_chmaps[]), but
had_register_chmap_ctls() never overrides the TLV callback installed
by snd_pcm_add_chmap_ctls(), so the generic pcm_chmap_ctl_tlv() from
ALSA core is left in place.

pcm_chmap_ctl_tlv() is reachable by any local user via
SNDRV_CTL_IOCTL_TLV_READ on the "Playback Channel Map" control and
walks the array with "for (map = info->chmap; map->channels; map++)".
Since the driver's single element is never terminated, this walks
past the allocation. The same pointer is also freed on hot-unplug and
rebuilt on hot-plug under intelhaddata->mutex, while the TLV callback
runs under card->controls_rwsem without that mutex, so the walk can
also race a concurrent free of the array.

Fix this by allocating a second, zeroed element so the array is
properly terminated, and by dropping the inherited TLV callback
entirely at registration time, since the driver never implements one
of its own.

Fixes: 5dab11d89777 ("ALSA: x86: hdmi: Add audio support for BYT and CHT")
Cc: stable@vger.kernel.org
Signed-off-by: Peter Ujfalusi <peter.ujfalusi@linux.intel.com>
---
 sound/x86/intel_hdmi_audio.c | 9 ++++++++-
 1 file changed, 8 insertions(+), 1 deletion(-)

diff --git a/sound/x86/intel_hdmi_audio.c b/sound/x86/intel_hdmi_audio.c
index 9f67244d4946..542fc35ec9b7 100644
--- a/sound/x86/intel_hdmi_audio.c
+++ b/sound/x86/intel_hdmi_audio.c
@@ -475,7 +475,8 @@ static void had_build_channel_allocation_map(struct snd_intelhad *intelhaddata)
 	kfree(intelhaddata->chmap->chmap);
 	intelhaddata->chmap->chmap = NULL;
 
-	chmap = kzalloc_obj(*chmap);
+	/* info->chmap must be zero-terminated; allocate a spare terminator entry */
+	chmap = kzalloc_objs(*chmap, 2);
 	if (!chmap)
 		return;
 
@@ -575,6 +576,12 @@ static int had_register_chmap_ctls(struct snd_intelhad *intelhaddata,
 	intelhaddata->chmap->kctl->info = had_chmap_ctl_info;
 	intelhaddata->chmap->kctl->get = had_chmap_ctl_get;
 	intelhaddata->chmap->chmap = NULL;
+
+	/* drop the inherited TLV read: it walks chmap without our mutex */
+	intelhaddata->chmap->kctl->tlv.c = NULL;
+	intelhaddata->chmap->kctl->vd[0].access &=
+		~(SNDRV_CTL_ELEM_ACCESS_TLV_READ | SNDRV_CTL_ELEM_ACCESS_TLV_CALLBACK);
+
 	return 0;
 }
 
-- 
2.56.0