[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>

2 files changed, 13 insertions, 5 deletions

diff --git a/include/media/media-device.h b/include/media/media-device.h
index a9b33c47310d..f743ae2210ee 100644
--- a/include/media/media-device.h
+++ b/include/media/media-device.h
@@ -347,7 +347,7 @@ struct media_entity_notify {
 struct media_device {
 	/* dev->driver_data points to this struct. */
 	struct device *dev;
-	struct media_devnode devnode;
+	struct media_devnode *devnode;
 
 	char model[32];
 	char driver_name[32];
@@ -393,9 +393,6 @@ struct usb_device;
 #define MEDIA_DEV_NOTIFY_PRE_LINK_CH	0
 #define MEDIA_DEV_NOTIFY_POST_LINK_CH	1
 
-/* media_devnode to media_device */
-#define to_media_device(node) container_of(node, struct media_device, devnode)
-
 /**
  * media_entity_enum_init - Initialise an entity enumeration
  *
diff --git a/include/media/media-devnode.h b/include/media/media-devnode.h
index e1d5af077adb..5bb3b0e86d73 100644
--- a/include/media/media-devnode.h
+++ b/include/media/media-devnode.h
@@ -33,6 +33,8 @@
 #include <linux/device.h>
 #include <linux/cdev.h>
 
+struct media_device;
+
 /*
  * Flag to mark the media_devnode struct as registered. Drivers must not touch
  * this flag directly, it will be set and cleared by media_devnode_register and
@@ -81,6 +83,8 @@ struct media_file_operations {
  * before registering the node.
  */
 struct media_devnode {
+	struct media_device *media_dev;
+
 	/* device ops */
 	const struct media_file_operations *fops;
 
@@ -103,6 +107,7 @@ struct media_devnode {
 /**
  * media_devnode_register - register a media device node
  *
+ * @media_dev: struct media_device we want to register a device node
  * @devnode: media device node structure we want to register
  * @owner: should be filled with %THIS_MODULE
  *
@@ -116,7 +121,8 @@ struct media_devnode {
  * the media_devnode structure is *not* called, so the caller is responsible for
  * freeing any data.
  */
-int __must_check media_devnode_register(struct media_devnode *devnode,
+int __must_check media_devnode_register(struct media_device *mdev,
+					struct media_devnode *devnode,
 					struct module *owner);
 
 /**
@@ -146,9 +152,14 @@ static inline struct media_devnode *media_devnode_data(struct file *filp)
  *	false otherwise.
  *
  * @devnode: pointer to struct &media_devnode.
+ *
+ * Note: If mdev is NULL, it also returns false.
  */
 static inline int media_devnode_is_registered(struct media_devnode *devnode)
 {
+	if (!devnode)
+		return false;
+
 	return test_bit(MEDIA_FLAG_REGISTERED, &devnode->flags);
 }