media: dvb-core: Fix use-after-free due to race at dvb_register_device()

dvb_register_device() dynamically allocates fops with kmemdup()
to set the fops->owner.
And these fops are registered in 'file->f_ops' using replace_fops()
in the dvb_device_open() process, and kfree()d in dvb_free_device().

However, it is not common to use dynamically allocated fops instead
of 'static const' fops as an argument of replace_fops(),
and UAF may occur.
These UAFs can occur on any dvb type using dvb_register_device(),
such as dvb_dvr, dvb_demux, dvb_frontend, dvb_net, etc.

So, instead of kfree() the fops dynamically allocated in
dvb_register_device() in dvb_free_device() called during the
.disconnect() process, kfree() it collectively in exit_dvbdev()
called when the dvbdev.c module is removed.

Link: https://lore.kernel.org/linux-media/[email protected]
Signed-off-by: Hyunwoo Kim <[email protected]>
Reported-by: kernel test robot <[email protected]>
Reported-by: Dan Carpenter <[email protected]>
Signed-off-by: Mauro Carvalho Chehab <[email protected]>

1 files changed, 15 insertions, 0 deletions

diff --git a/include/media/dvbdev.h b/include/media/dvbdev.h
index 29d25c8a6f13..8958e5e2fc5b 100644
--- a/include/media/dvbdev.h
+++ b/include/media/dvbdev.h
@@ -194,6 +194,21 @@ struct dvb_device {
 };
 
 /**
+ * struct dvbdevfops_node - fops nodes registered in dvbdevfops_list
+ *
+ * @fops:		Dynamically allocated fops for ->owner registration
+ * @type:		type of dvb_device
+ * @template:		dvb_device used for registration
+ * @list_head:		list_head for dvbdevfops_list
+ */
+struct dvbdevfops_node {
+	struct file_operations *fops;
+	enum dvb_device_type type;
+	const struct dvb_device *template;
+	struct list_head list_head;
+};
+
+/**
  * dvb_device_get - Increase dvb_device reference
  *
  * @dvbdev:	pointer to struct dvb_device