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: ed180abba7f1 ("ALSA: hda: Fix race between creating and refreshing sysfs entries")

Signed-off-by: Evan Green evgreen@chromium.org

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Changes in v3: - Moved locking back into callers (Takashi) - Combined update_widgets exit flow (Takashi)

Changes in v2: - Introduced widget_mutex relocation

sound/hda/hdac_device.c | 18 ++++++++++++------ 1 file changed, 12 insertions(+), 6 deletions(-)

diff --git a/sound/hda/hdac_device.c b/sound/hda/hdac_device.c index 6907dbefd08c..3842f9d34b7c 100644 --- a/sound/hda/hdac_device.c +++ b/sound/hda/hdac_device.c @@ -400,27 +400,33 @@ 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);