media-device: dynamically allocate struct media_devnode

commit a087ce704b802becbb4b0f2a20f2cb3f6911802e upstream.

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>
[bwh: Backported to 4.4:
 - Drop change in au0828
 - Include <linux/slab.h> in media-device.c
 - Adjust context]
Signed-off-by: Ben Hutchings <ben.hutchings@codethink.co.uk>
Signed-off-by: Sasha Levin <sashal@kernel.org>

2 files changed, 10 insertions, 5 deletions

diff --git a/include/media/media-device.h b/include/media/media-device.h
index 6e6db78f1ee2..00bbd679864a 100644
--- a/include/media/media-device.h
+++ b/include/media/media-device.h
@@ -60,7 +60,7 @@ struct device;
 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 serial[40];
@@ -84,9 +84,6 @@ struct media_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)
-
 int __must_check __media_device_register(struct media_device *mdev,
 					 struct module *owner);
 #define media_device_register(mdev) __media_device_register(mdev, THIS_MODULE)
diff --git a/include/media/media-devnode.h b/include/media/media-devnode.h
index 79f702d26d1f..8b854c044032 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
@@ -67,6 +69,8 @@ struct media_file_operations {
  * before registering the node.
  */
 struct media_devnode {
+	struct media_device *media_dev;
+
 	/* device ops */
 	const struct media_file_operations *fops;
 
@@ -86,7 +90,8 @@ struct media_devnode {
 /* dev to media_devnode */
 #define to_media_devnode(cd) container_of(cd, struct media_devnode, dev)
 
-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);
 void media_devnode_unregister(struct media_devnode *devnode);
 
@@ -97,6 +102,9 @@ static inline struct media_devnode *media_devnode_data(struct file *filp)
 
 static inline int media_devnode_is_registered(struct media_devnode *devnode)
 {
+	if (!devnode)
+		return false;
+
 	return test_bit(MEDIA_FLAG_REGISTERED, &devnode->flags);
 }