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

[Elena Reshetova <elena.reshetova@xxxxxxxxx>]

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


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