[PATCH 14/29] drivers, media: convert vb2_dc_buf.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-dma-contig.c | 11 ++++++-----
 1 file changed, 6 insertions(+), 5 deletions(-)

diff --git a/drivers/media/v4l2-core/videobuf2-dma-contig.c b/drivers/media/v4l2-core/videobuf2-dma-contig.c
index fb6a177..d29a07f 100644
--- a/drivers/media/v4l2-core/videobuf2-dma-contig.c
+++ b/drivers/media/v4l2-core/videobuf2-dma-contig.c
@@ -12,6 +12,7 @@
 
 #include <linux/dma-buf.h>
 #include <linux/module.h>
+#include <linux/refcount.h>
 #include <linux/scatterlist.h>
 #include <linux/sched.h>
 #include <linux/slab.h>
@@ -34,7 +35,7 @@ struct vb2_dc_buf {
 
 	/* MMAP related */
 	struct vb2_vmarea_handler	handler;
-	atomic_t			refcount;
+	refcount_t			refcount;
 	struct sg_table			*sgt_base;
 
 	/* DMABUF related */
@@ -86,7 +87,7 @@ static unsigned int vb2_dc_num_users(void *buf_priv)
 {
 	struct vb2_dc_buf *buf = buf_priv;
 
-	return atomic_read(&buf->refcount);
+	return refcount_read(&buf->refcount);
 }
 
 static void vb2_dc_prepare(void *buf_priv)
@@ -122,7 +123,7 @@ static void vb2_dc_put(void *buf_priv)
 {
 	struct vb2_dc_buf *buf = buf_priv;
 
-	if (!atomic_dec_and_test(&buf->refcount))
+	if (!refcount_dec_and_test(&buf->refcount))
 		return;
 
 	if (buf->sgt_base) {
@@ -170,7 +171,7 @@ static void *vb2_dc_alloc(struct device *dev, unsigned long attrs,
 	buf->handler.put = vb2_dc_put;
 	buf->handler.arg = buf;
 
-	atomic_inc(&buf->refcount);
+	refcount_set(&buf->refcount, 1);
 
 	return buf;
 }
@@ -407,7 +408,7 @@ static struct dma_buf *vb2_dc_get_dmabuf(void *buf_priv, unsigned long flags)
 		return NULL;
 
 	/* dmabuf keeps reference to vb2 buffer */
-	atomic_inc(&buf->refcount);
+	refcount_inc(&buf->refcount);
 
 	return dbuf;
 }
-- 
2.7.4