drm/rockchip: Use struct_size() in devm_kzalloc()

One of the more common cases of allocation size calculations is finding
the size of a structure that has a zero-sized array at the end, along
with memory for some number of elements for that array. For example:

struct foo {
	int stuff;
        void *entry[];
};

instance = devm_kzalloc(dev, sizeof(struct foo) + sizeof(void *) * count, GFP_KERNEL);

or, like in this particular case:

size = sizeof(struct foo) + sizeof(void *) * count;
instance = devm_kzalloc(dev, size, GFP_KERNEL);

Instead of leaving these open-coded and prone to type mistakes, we can
now use the new struct_size() helper:

instance = devm_kzalloc(dev, struct_size(instance, entry, count),
GFP_KERNEL);

This issue was detected with the help of Coccinelle.

Signed-off-by: Gustavo A. R. Silva <gustavo@embeddedor.com>
Reviewed-by: Kees Cook <keescook@chromium.org>
Signed-off-by: Heiko Stuebner <heiko@sntech.de>
Link: https://patchwork.freedesktop.org/patch/msgid/20180826184712.GA9330@embeddedor.com

diff --git a/drivers/gpu/drm/rockchip/rockchip_drm_vop.c b/drivers/gpu/drm/rockchip/rockchip_drm_vop.c
index 38f8cae..17f9ed6 100644 (file)
--- a/drivers/gpu/drm/rockchip/rockchip_drm_vop.c
+++ b/drivers/gpu/drm/rockchip/rockchip_drm_vop.c
@@ -32,6 +32,7 @@
 #include <linux/of_device.h>
 #include <linux/pm_runtime.h>
 #include <linux/component.h>
+#include <linux/overflow.h>
 
 #include <linux/reset.h>
 #include <linux/delay.h>
@@ -1579,7 +1580,6 @@ static int vop_bind(struct device *dev, struct device *master, void *data)
        struct drm_device *drm_dev = data;
        struct vop *vop;
        struct resource *res;
-       size_t alloc_size;
        int ret, irq;
 
        vop_data = of_device_get_match_data(dev);
@@ -1587,8 +1587,8 @@ static int vop_bind(struct device *dev, struct device *master, void *data)
                return -ENODEV;
 
        /* Allocate vop struct and its vop_win array */
-       alloc_size = sizeof(*vop) + sizeof(*vop->win) * vop_data->win_size;
-       vop = devm_kzalloc(dev, alloc_size, GFP_KERNEL);
+       vop = devm_kzalloc(dev, struct_size(vop, win, vop_data->win_size),
+                          GFP_KERNEL);
        if (!vop)
                return -ENOMEM;