Commit 98482377 authored Jul 01, 2019 by Evan Green Committed by Takashi Iwai Jul 01, 2019

ALSA: hda: Fix widget_mutex incomplete protection

The widget_mutex was introduced to serialize callers to
hda_widget_sysfs_{re}init. However, its protection of the sysfs widget array
is incomplete. For example, it is acquired around the call to
hda_widget_sysfs_reinit(), which actually creates the new array, but isn't
still acquired when codec->num_nodes and codec->start_nid is updated. So
the lock ensures one thread sets up the new array at a time, but doesn't
ensure which thread's value will end up in codec->num_nodes. If a larger
num_nodes wins but a smaller array was set up, the next call to
refresh_widgets() will touch free memory as it iterates over codec->num_nodes
that aren't there.

The widget_lock really protects both the tree as well as codec->num_nodes,
start_nid, and end_nid, so make sure it's held across that update. It should
also be held during snd_hdac_get_sub_nodes(), so that a very old read from that
function doesn't end up clobbering a later update.

Fixes: ed180abb ("ALSA: hda: Fix race between creating and refreshing sysfs entries")
Signed-off-by: Evan Green <evgreen@chromium.org>
Signed-off-by: Takashi Iwai <tiwai@suse.de>

parent 7fbd1753

sound/hda/hdac_device.c

+12 −6

Original line number	Diff line number	Diff line
		@@ -399,27 +399,33 @@ static void setup_fg_nodes(struct hdac_device *codec)
		int snd_hdac_refresh_widgets(struct hdac_device *codec, bool sysfs)
		{
		hda_nid_t start_nid;
		int nums, err;
		int nums, err = 0;

		/*
		* Serialize against multiple threads trying to update the sysfs
		* widgets array.
		*/
		mutex_lock(&codec->widget_lock);
		nums = snd_hdac_get_sub_nodes(codec, codec->afg, &start_nid);
		if (!start_nid \|\| nums <= 0 \|\| nums >= 0xff) {
		dev_err(&codec->dev, "cannot read sub nodes for FG 0x%02x\n",
		codec->afg);
		return -EINVAL;
		err = -EINVAL;
		goto unlock;
		}

		if (sysfs) {
		mutex_lock(&codec->widget_lock);
		err = hda_widget_sysfs_reinit(codec, start_nid, nums);
		mutex_unlock(&codec->widget_lock);
		if (err < 0)
		return err;
		goto unlock;
		}

		codec->num_nodes = nums;
		codec->start_nid = start_nid;
		codec->end_nid = start_nid + nums;
		return 0;
		unlock:
		mutex_unlock(&codec->widget_lock);
		return err;
		}
		EXPORT_SYMBOL_GPL(snd_hdac_refresh_widgets);

Admin message