ALSA: fireface: add field for the number of messages copied to user space

Current structure includes no field to express the number of messages
copied to user space, thus user space application needs to information
out of the structure to parse the content of structure.

This commit adds a field to express the number of messages copied to user
space since It is more preferable to use self-contained structure.

Kees Cook proposed an idea of annotation for bound of flexible arrays
in his future improvement for flexible-length array in kernel. The
additional field for message count is suitable to the idea as well.

Reference: https://people.kernel.org/kees/bounded-flexible-arrays-in-c
Signed-off-by: Takashi Sakamoto <o-takashi@sakamocchi.jp>
Link: https://lore.kernel.org/r/20230202133708.163936-1-o-takashi@sakamocchi.jp
Signed-off-by: Takashi Iwai <tiwai@suse.de>

1 files changed, 16 insertions, 12 deletions

diff --git a/sound/firewire/fireface/ff-protocol-former.c b/sound/firewire/fireface/ff-protocol-former.c
index fa41de978756..efd59e9d9935 100644
--- a/sound/firewire/fireface/ff-protocol-former.c
+++ b/sound/firewire/fireface/ff-protocol-former.c
@@ -677,23 +677,19 @@ static void ff400_handle_msg(struct snd_ff *ff, unsigned int offset, const __le3
 
 static long ff400_copy_msg_to_user(struct snd_ff *ff, char __user *buf, long count)
 {
+	struct snd_firewire_event_ff400_message ev = {
+		.type = SNDRV_FIREWIRE_EVENT_FF400_MESSAGE,
+		.message_count = 0,
+	};
 	struct ff400_msg_parser *parser = ff->msg_parser;
-	u32 type = SNDRV_FIREWIRE_EVENT_FF400_MESSAGE;
 	long consumed = 0;
-	int ret = 0;
+	long ret = 0;
 
-	if (count < 8)
+	if (count < sizeof(ev) || parser->pull_pos == parser->push_pos)
 		return 0;
 
-	spin_unlock_irq(&ff->lock);
-	if (copy_to_user(buf, &type, sizeof(type)))
-		ret = -EFAULT;
-	spin_lock_irq(&ff->lock);
-	if (ret)
-		return ret;
-
-	count -= sizeof(type);
-	consumed += sizeof(type);
+	count -= sizeof(ev);
+	consumed += sizeof(ev);
 
 	while (count >= sizeof(*parser->msgs) && parser->pull_pos != parser->push_pos) {
 		spin_unlock_irq(&ff->lock);
@@ -707,10 +703,18 @@ static long ff400_copy_msg_to_user(struct snd_ff *ff, char __user *buf, long cou
 		++parser->pull_pos;
 		if (parser->pull_pos >= FF400_QUEUE_SIZE)
 			parser->pull_pos = 0;
+		++ev.message_count;
 		count -= sizeof(*parser->msgs);
 		consumed += sizeof(*parser->msgs);
 	}
 
+	spin_unlock_irq(&ff->lock);
+	if (copy_to_user(buf, &ev, sizeof(ev)))
+		ret = -EFAULT;
+	spin_lock_irq(&ff->lock);
+	if (ret)
+		return ret;
+
 	return consumed;
 }