ALSA: rawmidi: Change resized buffers atomically

Commit Message

Takashi Iwai July 17, 2018, 5:53 p.m. UTC

The SNDRV_RAWMIDI_IOCTL_PARAMS ioctl may resize the buffers and the
current code is racy.  For example, the sequencer client may write to
buffer while it being resized.

As a simple workaround, let's switch to the resized buffer inside the
stream runtime lock.

Reported-by: [e-mail]
Cc: <[e-mail]>
Signed-off-by: Takashi Iwai <[e-mail]>
---
 sound/core/rawmidi.c | 20 ++++++++++++++------
 1 file changed, 14 insertions(+), 6 deletions(-)

Patch

diff --git a/sound/core/rawmidi.c b/sound/core/rawmidi.c
index 69616d00481c..b53026a72e73 100644
--- a/sound/core/rawmidi.c
+++ b/sound/core/rawmidi.c
@@ -635,7 +635,7 @@  static int snd_rawmidi_info_select_user(struct snd_card *card,
 int snd_rawmidi_output_params(struct snd_rawmidi_substream *substream,
 			      struct snd_rawmidi_params * params)
 {
-	char *newbuf;
+	char *newbuf, *oldbuf;
 	struct snd_rawmidi_runtime *runtime = substream->runtime;
 	
 	if (substream->append && substream->use_count > 1)
@@ -648,13 +648,17 @@  int snd_rawmidi_output_params(struct snd_rawmidi_substream *substream,
 		return -EINVAL;
 	}
 	if (params->buffer_size != runtime->buffer_size) {
-		newbuf = krealloc(runtime->buffer, params->buffer_size,
-				  GFP_KERNEL);
+		newbuf = kmalloc(params->buffer_size, GFP_KERNEL);
 		if (!newbuf)
 			return -ENOMEM;
+		spin_lock_irq(&runtime->lock);
+		oldbuf = runtime->buffer;
 		runtime->buffer = newbuf;
 		runtime->buffer_size = params->buffer_size;
 		runtime->avail = runtime->buffer_size;
+		runtime->appl_ptr = runtime->hw_ptr = 0;
+		spin_unlock_irq(&runtime->lock);
+		kfree(oldbuf);
 	}
 	runtime->avail_min = params->avail_min;
 	substream->active_sensing = !params->no_active_sensing;
@@ -665,7 +669,7 @@  EXPORT_SYMBOL(snd_rawmidi_output_params);
 int snd_rawmidi_input_params(struct snd_rawmidi_substream *substream,
 			     struct snd_rawmidi_params * params)
 {
-	char *newbuf;
+	char *newbuf, *oldbuf;
 	struct snd_rawmidi_runtime *runtime = substream->runtime;
 
 	snd_rawmidi_drain_input(substream);
@@ -676,12 +680,16 @@  int snd_rawmidi_input_params(struct snd_rawmidi_substream *substream,
 		return -EINVAL;
 	}
 	if (params->buffer_size != runtime->buffer_size) {
-		newbuf = krealloc(runtime->buffer, params->buffer_size,
-				  GFP_KERNEL);
+		newbuf = kmalloc(params->buffer_size, GFP_KERNEL);
 		if (!newbuf)
 			return -ENOMEM;
+		spin_lock_irq(&runtime->lock);
+		oldbuf = runtime->buffer;
 		runtime->buffer = newbuf;
 		runtime->buffer_size = params->buffer_size;
+		runtime->appl_ptr = runtime->hw_ptr = 0;
+		spin_unlock_irq(&runtime->lock);
+		kfree(oldbuf);
 	}
 	runtime->avail_min = params->avail_min;
 	return 0;