[PATCH] Drivers: hv: vmbus: Add mutex lock to channel show functions

[Kimberly Brown]

The channel level "_show" functions are vulnerable to race conditions.
Add a mutex lock and unlock around the call to the channel level "_show"
functions in vmbus_chan_attr_show().

This problem was discussed here: https://lkml.org/lkml/2018/10/18/830

Signed-off-by: Kimberly Brown <kimbrownkd@xxxxxxxxx>
---
 drivers/hv/vmbus_drv.c | 6 +++++-
 1 file changed, 5 insertions(+), 1 deletion(-)

diff --git a/drivers/hv/vmbus_drv.c b/drivers/hv/vmbus_drv.c
index 403fee01572c..e8189bc168da 100644
--- a/drivers/hv/vmbus_drv.c
+++ b/drivers/hv/vmbus_drv.c
@@ -1414,6 +1414,7 @@ static ssize_t vmbus_chan_attr_show(struct kobject *kobj,
 		= container_of(attr, struct vmbus_chan_attribute, attr);
 	const struct vmbus_channel *chan
 		= container_of(kobj, struct vmbus_channel, kobj);
+	ssize_t ret;
 
 	if (!attribute->show)
 		return -EIO;
@@ -1421,7 +1422,10 @@ static ssize_t vmbus_chan_attr_show(struct kobject *kobj,
 	if (chan->state != CHANNEL_OPENED_STATE)
 		return -EINVAL;
 
-	return attribute->show(chan, buf);
+	mutex_lock(&vmbus_connection.channel_mutex);
+	ret = attribute->show(chan, buf);
+	mutex_unlock(&vmbus_connection.channel_mutex);
+	return ret;
 }
 
 static const struct sysfs_ops vmbus_chan_sysfs_ops = {
-- 
2.17.1