ALSA: rawmidi: Initialize allocated buffers

syzbot reported the uninitialized value exposure in certain situations
using virmidi loop.  It's likely a very small race at writing and
reading, and the influence is almost negligible.  But it's safer to
paper over this just by replacing the existing kvmalloc() with
kvzalloc().

Reported-by: syzbot+194dffdb8b22fc5d207a@syzkaller.appspotmail.com
Signed-off-by: Takashi Iwai <tiwai@suse.de>

sound/core/rawmidi.c

@@ -129,7 +129,7 @@ static int snd_rawmidi_runtime_create(struct snd_rawmidi_substream *substream)
 		runtime->avail = 0;
 	else
 		runtime->avail = runtime->buffer_size;
-	runtime->buffer = kvmalloc(runtime->buffer_size, GFP_KERNEL);
+	runtime->buffer = kvzalloc(runtime->buffer_size, GFP_KERNEL);
 	if (!runtime->buffer) {
 		kfree(runtime);
 		return -ENOMEM;
@@ -655,7 +655,7 @@ static int resize_runtime_buffer(struct snd_rawmidi_runtime *runtime,
 	if (params->avail_min < 1 || params->avail_min > params->buffer_size)
 		return -EINVAL;
 	if (params->buffer_size != runtime->buffer_size) {
-		newbuf = kvmalloc(params->buffer_size, GFP_KERNEL);
+		newbuf = kvzalloc(params->buffer_size, GFP_KERNEL);
 		if (!newbuf)
 			return -ENOMEM;
 		spin_lock_irq(&runtime->lock);