[PATCH 4/5] ALSA: rawmidi: Check stream state at exported functions

[Takashi Iwai]

The rawmidi interface provides some exported functions to be called
from outside, and currently there is no state check for those calls
whether the stream is properly opened and running.  Although such an
invalid call shouldn't happen, but who knows.

This patch adds the proper rawmidi stream state checks with spinlocks
for avoiding unexpected accesses when such exported functions are
called in an invalid state.  After this patch, with the
substream->opened and substream->runtime are always tied and
guaranteed to be set under substream->lock.

Signed-off-by: Takashi Iwai <tiwai at suse.de>
---
 sound/core/rawmidi.c | 56 ++++++++++++++++++++++++++++++--------------
 1 file changed, 38 insertions(+), 18 deletions(-)

diff --git a/sound/core/rawmidi.c b/sound/core/rawmidi.c
index 7fd6b369d46f..889fa4747dad 100644
--- a/sound/core/rawmidi.c
+++ b/sound/core/rawmidi.c
@@ -207,7 +207,8 @@ static void reset_runtime_ptrs(struct snd_rawmidi_substream *substream,
 	unsigned long flags;
 
 	spin_lock_irqsave(&substream->lock, flags);
-	__reset_runtime_ptrs(substream->runtime, is_input);
+	if (substream->opened && substream->runtime)
+		__reset_runtime_ptrs(substream->runtime, is_input);
 	spin_unlock_irqrestore(&substream->lock, flags);
 }
 
@@ -309,12 +310,14 @@ static int open_substream(struct snd_rawmidi *rmidi,
 			snd_rawmidi_runtime_free(substream);
 			return err;
 		}
+		spin_lock_irq(&substream->lock);
 		substream->opened = 1;
 		substream->active_sensing = 0;
 		if (mode & SNDRV_RAWMIDI_LFLG_APPEND)
 			substream->append = 1;
 		substream->pid = get_pid(task_pid(current));
 		rmidi->streams[substream->stream].substream_opened++;
+		spin_unlock_irq(&substream->lock);
 	}
 	substream->use_count++;
 	return 0;
@@ -520,12 +523,14 @@ static void close_substream(struct snd_rawmidi *rmidi,
 				snd_rawmidi_output_trigger(substream, 0);
 		}
 	}
+	spin_lock_irq(&substream->lock);
+	substream->opened = 0;
+	substream->append = 0;
+	spin_unlock_irq(&substream->lock);
 	substream->ops->close(substream);
 	if (substream->runtime->private_free)
 		substream->runtime->private_free(substream);
 	snd_rawmidi_runtime_free(substream);
-	substream->opened = 0;
-	substream->append = 0;
 	put_pid(substream->pid);
 	substream->pid = NULL;
 	rmidi->streams[substream->stream].substream_opened--;
@@ -1074,17 +1079,21 @@ int snd_rawmidi_receive(struct snd_rawmidi_substream *substream,
 	unsigned long flags;
 	struct timespec64 ts64 = get_framing_tstamp(substream);
 	int result = 0, count1;
-	struct snd_rawmidi_runtime *runtime = substream->runtime;
+	struct snd_rawmidi_runtime *runtime;
 
-	if (!substream->opened)
-		return -EBADFD;
-	if (runtime->buffer == NULL) {
+	spin_lock_irqsave(&substream->lock, flags);
+	if (!substream->opened) {
+		result = -EBADFD;
+		goto unlock;
+	}
+	runtime = substream->runtime;
+	if (!runtime || !runtime->buffer) {
 		rmidi_dbg(substream->rmidi,
 			  "snd_rawmidi_receive: input is not active!!!\n");
-		return -EINVAL;
+		result = -EINVAL;
+		goto unlock;
 	}
 
-	spin_lock_irqsave(&substream->lock, flags);
 	if (substream->framing == SNDRV_RAWMIDI_MODE_FRAMING_TSTAMP) {
 		result = receive_with_tstamp_framing(substream, buffer, count, &ts64);
 	} else if (count == 1) {	/* special case, faster code */
@@ -1131,6 +1140,7 @@ int snd_rawmidi_receive(struct snd_rawmidi_substream *substream,
 		else if (__snd_rawmidi_ready(runtime))
 			wake_up(&runtime->sleep);
 	}
+ unlock:
 	spin_unlock_irqrestore(&substream->lock, flags);
 	return result;
 }
@@ -1252,17 +1262,19 @@ static ssize_t snd_rawmidi_read(struct file *file, char __user *buf, size_t coun
  */
 int snd_rawmidi_transmit_empty(struct snd_rawmidi_substream *substream)
 {
-	struct snd_rawmidi_runtime *runtime = substream->runtime;
+	struct snd_rawmidi_runtime *runtime;
 	int result;
 	unsigned long flags;
 
-	if (runtime->buffer == NULL) {
+	spin_lock_irqsave(&substream->lock, flags);
+	runtime = substream->runtime;
+	if (!substream->opened || !runtime || !runtime->buffer) {
 		rmidi_dbg(substream->rmidi,
 			  "snd_rawmidi_transmit_empty: output is not active!!!\n");
-		return 1;
+		result = 1;
+	} else {
+		result = runtime->avail >= runtime->buffer_size;
 	}
-	spin_lock_irqsave(&substream->lock, flags);
-	result = runtime->avail >= runtime->buffer_size;
 	spin_unlock_irqrestore(&substream->lock, flags);
 	return result;
 }
@@ -1336,7 +1348,10 @@ int snd_rawmidi_transmit_peek(struct snd_rawmidi_substream *substream,
 	unsigned long flags;
 
 	spin_lock_irqsave(&substream->lock, flags);
-	result = __snd_rawmidi_transmit_peek(substream, buffer, count);
+	if (!substream->opened || !substream->runtime)
+		result = -EBADFD;
+	else
+		result = __snd_rawmidi_transmit_peek(substream, buffer, count);
 	spin_unlock_irqrestore(&substream->lock, flags);
 	return result;
 }
@@ -1388,7 +1403,10 @@ int snd_rawmidi_transmit_ack(struct snd_rawmidi_substream *substream, int count)
 	unsigned long flags;
 
 	spin_lock_irqsave(&substream->lock, flags);
-	result = __snd_rawmidi_transmit_ack(substream, count);
+	if (!substream->opened || !substream->runtime)
+		result = -EBADFD;
+	else
+		result = __snd_rawmidi_transmit_ack(substream, count);
 	spin_unlock_irqrestore(&substream->lock, flags);
 	return result;
 }
@@ -1433,12 +1451,14 @@ EXPORT_SYMBOL(snd_rawmidi_transmit);
  */
 int snd_rawmidi_proceed(struct snd_rawmidi_substream *substream)
 {
-	struct snd_rawmidi_runtime *runtime = substream->runtime;
+	struct snd_rawmidi_runtime *runtime;
 	unsigned long flags;
 	int count = 0;
 
 	spin_lock_irqsave(&substream->lock, flags);
-	if (runtime->avail < runtime->buffer_size) {
+	runtime = substream->runtime;
+	if (substream->opened && runtime &&
+	    runtime->avail < runtime->buffer_size) {
 		count = runtime->buffer_size - runtime->avail;
 		__snd_rawmidi_transmit_ack(substream, count);
 	}
-- 
2.35.3