[media] media-device: dynamically allocate struct media_devnode

struct media_devnode is currently embedded at struct media_device.

While this works fine during normal usage, it leads to a race
condition during devnode unregister. the problem is that drivers
assume that, after calling media_device_unregister(), the struct
that contains media_device can be freed. This is not true, as it
can't be freed until userspace closes all opened /dev/media devnodes.

In other words, if the media devnode is still open, and media_device
gets freed, any call to an ioctl will make the core to try to access
struct media_device, with will cause an use-after-free and even GPF.

Fix this by dynamically allocating the struct media_devnode and only
freeing it when it is safe.

Signed-off-by: Mauro Carvalho Chehab <mchehab@osg.samsung.com>
Signed-off-by: Mauro Carvalho Chehab <mchehab@s-opensource.com>

1 files changed, 30 insertions, 14 deletions

diff --git a/drivers/media/media-device.c b/drivers/media/media-device.c
index a1cd50f331f1..e61fa66d95df 100644
--- a/drivers/media/media-device.c
+++ b/drivers/media/media-device.c
@@ -423,7 +423,7 @@ static long media_device_ioctl(struct file *filp, unsigned int cmd,
 			       unsigned long arg)
 {
 	struct media_devnode *devnode = media_devnode_data(filp);
-	struct media_device *dev = to_media_device(devnode);
+	struct media_device *dev = devnode->media_dev;
 	long ret;
 
 	mutex_lock(&dev->graph_mutex);
@@ -495,7 +495,7 @@ static long media_device_compat_ioctl(struct file *filp, unsigned int cmd,
 				      unsigned long arg)
 {
 	struct media_devnode *devnode = media_devnode_data(filp);
-	struct media_device *dev = to_media_device(devnode);
+	struct media_device *dev = devnode->media_dev;
 	long ret;
 
 	switch (cmd) {
@@ -531,7 +531,8 @@ static const struct media_file_operations media_device_fops = {
 static ssize_t show_model(struct device *cd,
 			  struct device_attribute *attr, char *buf)
 {
-	struct media_device *mdev = to_media_device(to_media_devnode(cd));
+	struct media_devnode *devnode = to_media_devnode(cd);
+	struct media_device *mdev = devnode->media_dev;
 
 	return sprintf(buf, "%.*s\n", (int)sizeof(mdev->model), mdev->model);
 }
@@ -704,23 +705,34 @@ EXPORT_SYMBOL_GPL(media_device_cleanup);
 int __must_check __media_device_register(struct media_device *mdev,
 					 struct module *owner)
 {
+	struct media_devnode *devnode;
 	int ret;
 
+	devnode = kzalloc(sizeof(*devnode), GFP_KERNEL);
+	if (!devnode)
+		return -ENOMEM;
+
 	/* Register the device node. */
-	mdev->devnode.fops = &media_device_fops;
-	mdev->devnode.parent = mdev->dev;
-	mdev->devnode.release = media_device_release;
+	mdev->devnode = devnode;
+	devnode->fops = &media_device_fops;
+	devnode->parent = mdev->dev;
+	devnode->release = media_device_release;
 
 	/* Set version 0 to indicate user-space that the graph is static */
 	mdev->topology_version = 0;
 
-	ret = media_devnode_register(&mdev->devnode, owner);
-	if (ret < 0)
+	ret = media_devnode_register(mdev, devnode, owner);
+	if (ret < 0) {
+		mdev->devnode = NULL;
+		kfree(devnode);
 		return ret;
+	}
 
-	ret = device_create_file(&mdev->devnode.dev, &dev_attr_model);
+	ret = device_create_file(&devnode->dev, &dev_attr_model);
 	if (ret < 0) {
-		media_devnode_unregister(&mdev->devnode);
+		mdev->devnode = NULL;
+		media_devnode_unregister(devnode);
+		kfree(devnode);
 		return ret;
 	}
 
@@ -771,7 +783,7 @@ void media_device_unregister(struct media_device *mdev)
 	mutex_lock(&mdev->graph_mutex);
 
 	/* Check if mdev was ever registered at all */
-	if (!media_devnode_is_registered(&mdev->devnode)) {
+	if (!media_devnode_is_registered(mdev->devnode)) {
 		mutex_unlock(&mdev->graph_mutex);
 		return;
 	}
@@ -794,9 +806,13 @@ void media_device_unregister(struct media_device *mdev)
 
 	mutex_unlock(&mdev->graph_mutex);
 
-	device_remove_file(&mdev->devnode.dev, &dev_attr_model);
-	dev_dbg(mdev->dev, "Media device unregistering\n");
-	media_devnode_unregister(&mdev->devnode);
+	dev_dbg(mdev->dev, "Media device unregistered\n");
+
+	/* Check if mdev devnode was registered */
+	if (media_devnode_is_registered(mdev->devnode)) {
+		device_remove_file(&mdev->devnode->dev, &dev_attr_model);
+		media_devnode_unregister(mdev->devnode);
+	}
 }
 EXPORT_SYMBOL_GPL(media_device_unregister);