[media] v4l2: vb2-dma-sg: fix potential security hole

Memory allocated by alloc_page() function might contain some potentially
important data from other system processes. The patch adds a flag to
zero the allocated page before giving it to videobuf2 (and then to
userspace).
Signed-off-by: NAndrzej Pietrasiewicz <andrzej.p@samsung.com>
Signed-off-by: NKyungmin Park <kyungmin.park@samsung.com>
Signed-off-by: NMarek Szyprowski <m.szyprowski@samsung.com>
Signed-off-by: NMauro Carvalho Chehab <mchehab@redhat.com>

drivers/media/video/videobuf2-dma-sg.c

@@ -62,7 +62,7 @@ static void *vb2_dma_sg_alloc(void *alloc_ctx, unsigned long size)
 		goto fail_pages_array_alloc;
 
 	for (i = 0; i < buf->sg_desc.num_pages; ++i) {
-		buf->pages[i] = alloc_page(GFP_KERNEL);
+		buf->pages[i] = alloc_page(GFP_KERNEL | __GFP_ZERO);
 		if (NULL == buf->pages[i])
 			goto fail_pages_alloc;
 		sg_set_page(&buf->sg_desc.sglist[i],