[PATCH 13/29] drivers, media: convert vb2_vmarea_handler.refcount from atomic_t to refcount_t

[Elena Reshetova]

refcount_t type and corresponding API should be
used instead of atomic_t when the variable is used as
a reference counter. This allows to avoid accidental
refcounter overflows that might lead to use-after-free
situations.

Signed-off-by: Elena Reshetova <elena.reshetova@xxxxxxxxx>
Signed-off-by: Hans Liljestrand <ishkamiel@xxxxxxxxx>
Signed-off-by: Kees Cook <keescook@xxxxxxxxxxxx>
Signed-off-by: David Windsor <dwindsor@xxxxxxxxx>
---
 drivers/media/v4l2-core/videobuf2-memops.c | 6 +++---
 include/media/videobuf2-memops.h           | 3 ++-
 2 files changed, 5 insertions(+), 4 deletions(-)

diff --git a/drivers/media/v4l2-core/videobuf2-memops.c b/drivers/media/v4l2-core/videobuf2-memops.c
index 1cd322e..4bb8424 100644
--- a/drivers/media/v4l2-core/videobuf2-memops.c
+++ b/drivers/media/v4l2-core/videobuf2-memops.c
@@ -96,10 +96,10 @@ static void vb2_common_vm_open(struct vm_area_struct *vma)
 	struct vb2_vmarea_handler *h = vma->vm_private_data;
 
 	pr_debug("%s: %p, refcount: %d, vma: %08lx-%08lx\n",
-	       __func__, h, atomic_read(h->refcount), vma->vm_start,
+	       __func__, h, refcount_read(h->refcount), vma->vm_start,
 	       vma->vm_end);
 
-	atomic_inc(h->refcount);
+	refcount_inc(h->refcount);
 }
 
 /**
@@ -114,7 +114,7 @@ static void vb2_common_vm_close(struct vm_area_struct *vma)
 	struct vb2_vmarea_handler *h = vma->vm_private_data;
 
 	pr_debug("%s: %p, refcount: %d, vma: %08lx-%08lx\n",
-	       __func__, h, atomic_read(h->refcount), vma->vm_start,
+	       __func__, h, refcount_read(h->refcount), vma->vm_start,
 	       vma->vm_end);
 
 	h->put(h->arg);
diff --git a/include/media/videobuf2-memops.h b/include/media/videobuf2-memops.h
index 36565c7a..a6ed091 100644
--- a/include/media/videobuf2-memops.h
+++ b/include/media/videobuf2-memops.h
@@ -16,6 +16,7 @@
 
 #include <media/videobuf2-v4l2.h>
 #include <linux/mm.h>
+#include <linux/refcount.h>
 
 /**
  * struct vb2_vmarea_handler - common vma refcount tracking handler
@@ -25,7 +26,7 @@
  * @arg:	argument for @put callback
  */
 struct vb2_vmarea_handler {
-	atomic_t		*refcount;
+	refcount_t		*refcount;
 	void			(*put)(void *arg);
 	void			*arg;
 };
-- 
2.7.4