[PATCH v4 4/5] ALSA: pcm: Refuse to open a disconnected PCM

[Cen Zhang <zzzccc427@gmail.com>]

An open that found the PCM before snd_pcm_dev_disconnect() can still
attach a substream after it, because nothing in the open path checks
whether the PCM was disconnected. When only the PCM is disconnected, as
on an HD-audio codec unbind, the open then succeeds on a device that is
going away, and its file delays the remove until it is closed.

Mark the PCM as disconnected under open_mutex in snd_pcm_dev_disconnect()
and make snd_pcm_attach_substream() fail with -ENODEV for it.

Signed-off-by: Cen Zhang <zzzccc427@gmail.com>
---
 include/sound/pcm.h | 1 +
 sound/core/pcm.c    | 3 +++
 2 files changed, 4 insertions(+)

diff --git a/include/sound/pcm.h b/include/sound/pcm.h
index 1cf511f8d880..04f58c2ec5c6 100644
--- a/include/sound/pcm.h
+++ b/include/sound/pcm.h
@@ -548,6 +548,7 @@ struct snd_pcm {
 	bool internal; /* pcm is for internal use only */
 	bool nonatomic; /* whole PCM operations are in non-atomic context */
 	bool no_device_suspend; /* don't invoke device PM suspend */
+	bool disconnected; /* disconnected, no new open */
 #if IS_ENABLED(CONFIG_SND_PCM_OSS)
 	struct snd_pcm_oss oss;
 #endif
diff --git a/sound/core/pcm.c b/sound/core/pcm.c
index 064df4cd3b50..567eeff23095 100644
--- a/sound/core/pcm.c
+++ b/sound/core/pcm.c
@@ -897,6 +897,8 @@ int snd_pcm_attach_substream(struct snd_pcm *pcm, int stream,
 		       stream != SNDRV_PCM_STREAM_CAPTURE))
 		return -EINVAL;
 	*rsubstream = NULL;
+	if (pcm->disconnected)
+		return -ENODEV;
 	pstr = &pcm->streams[stream];
 	if (pstr->substream == NULL || pstr->substream_count == 0)
 		return -ENODEV;
@@ -1101,6 +1103,7 @@ static int snd_pcm_dev_disconnect(struct snd_device *device)
 
 	guard(mutex)(&register_mutex);
 	scoped_guard(mutex, &pcm->open_mutex) {
+		pcm->disconnected = true;
 		wake_up(&pcm->open_wait);
 		list_del_init(&pcm->list);