[Xen-devel] [PATCH 15/29] drivers, media: convert vb2_dma_sg_buf.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-dma-sg.c | 11 ++++++-----
 1 file changed, 6 insertions(+), 5 deletions(-)

diff --git a/drivers/media/v4l2-core/videobuf2-dma-sg.c 
b/drivers/media/v4l2-core/videobuf2-dma-sg.c
index ecff8f4..29fde1a 100644
--- a/drivers/media/v4l2-core/videobuf2-dma-sg.c
+++ b/drivers/media/v4l2-core/videobuf2-dma-sg.c
@@ -12,6 +12,7 @@
 
 #include <linux/module.h>
 #include <linux/mm.h>
+#include <linux/refcount.h>
 #include <linux/scatterlist.h>
 #include <linux/sched.h>
 #include <linux/slab.h>
@@ -46,7 +47,7 @@ struct vb2_dma_sg_buf {
        struct sg_table                 *dma_sgt;
        size_t                          size;
        unsigned int                    num_pages;
-       atomic_t                        refcount;
+       refcount_t                      refcount;
        struct vb2_vmarea_handler       handler;
 
        struct dma_buf_attachment       *db_attach;
@@ -150,7 +151,7 @@ static void *vb2_dma_sg_alloc(struct device *dev, unsigned 
long dma_attrs,
        buf->handler.put = vb2_dma_sg_put;
        buf->handler.arg = buf;
 
-       atomic_inc(&buf->refcount);
+       refcount_set(&buf->refcount, 1);
 
        dprintk(1, "%s: Allocated buffer of %d pages\n",
                __func__, buf->num_pages);
@@ -176,7 +177,7 @@ static void vb2_dma_sg_put(void *buf_priv)
        struct sg_table *sgt = &buf->sg_table;
        int i = buf->num_pages;
 
-       if (atomic_dec_and_test(&buf->refcount)) {
+       if (refcount_dec_and_test(&buf->refcount)) {
                dprintk(1, "%s: Freeing buffer of %d pages\n", __func__,
                        buf->num_pages);
                dma_unmap_sg_attrs(buf->dev, sgt->sgl, sgt->orig_nents,
@@ -320,7 +321,7 @@ static unsigned int vb2_dma_sg_num_users(void *buf_priv)
 {
        struct vb2_dma_sg_buf *buf = buf_priv;
 
-       return atomic_read(&buf->refcount);
+       return refcount_read(&buf->refcount);
 }
 
 static int vb2_dma_sg_mmap(void *buf_priv, struct vm_area_struct *vma)
@@ -530,7 +531,7 @@ static struct dma_buf *vb2_dma_sg_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


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