[PATCH] rtc: sun6i: Use struct_size() in 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 = kzalloc(sizeof(struct foo) + sizeof(void *) * count, GFP_KERNEL);

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

instance = kzalloc(struct_size(instance, entry, count), GFP_KERNEL);

Signed-off-by: Gustavo A. R. Silva <redacted>
---
 drivers/rtc/rtc-sun6i.c | 3 +--
 1 file changed, 1 insertion(+), 2 deletions(-)

diff --git a/drivers/rtc/rtc-sun6i.c b/drivers/rtc/rtc-sun6i.c
index 2cd5a7b..fe07310 100644
--- a/drivers/rtc/rtc-sun6i.c
+++ b/drivers/rtc/rtc-sun6i.c

@@ -199,8 +199,7 @@ static void __init sun6i_rtc_clk_init(struct device_node *node)
 	if (!rtc)
 		return;
 
-	clk_data = kzalloc(sizeof(*clk_data) + (sizeof(*clk_data->hws) * 2),
-			   GFP_KERNEL);
+	clk_data = kzalloc(struct_size(clk_data, hws, 2), GFP_KERNEL);
 	if (!clk_data) {
 		kfree(rtc);
 		return;

-- 
2.7.4

On Thu, Aug 23, 2018 at 11:51 AM, Gustavo A. R. Silva
[off-list ref] wrote:

This looks like entirely correct to me, but I'm surprised the
Coccinelle script didn't discover this. I guess the isomorphisms don't
cover the parenthesis?

-Kees

-- 
Kees Cook
Pixel Security

On 8/23/18 3:56 PM, Kees Cook wrote:

quoted

-       clk_data = kzalloc(sizeof(*clk_data) + (sizeof(*clk_data->hws) * 2),
-                          GFP_KERNEL);
+       clk_data = kzalloc(struct_size(clk_data, hws, 2), GFP_KERNEL);
        if (!clk_data) {
                kfree(rtc);
                return;

This looks like entirely correct to me, but I'm surprised the
Coccinelle script didn't discover this. I guess the isomorphisms don't
cover the parenthesis?

Apparently.

If I manually remove the ()s, the cocci script successfully generates a patch.

--
Gustavo

On Thu, Aug 23, 2018 at 11:51 AM, Gustavo A. R. Silva
[off-list ref] wrote:

Reviewed-by: Kees Cook <redacted>

-Kees

-- 
Kees Cook
Pixel Security

On 23/08/2018 13:51:40-0500, Gustavo A. R. Silva wrote:

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 = kzalloc(sizeof(struct foo) + sizeof(void *) * count, GFP_KERNEL);

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

instance = kzalloc(struct_size(instance, entry, count), GFP_KERNEL);

Signed-off-by: Gustavo A. R. Silva <redacted>
---
 drivers/rtc/rtc-sun6i.c | 3 +--
 1 file changed, 1 insertion(+), 2 deletions(-)

Applied, thanks.

-- 
Alexandre Belloni, Bootlin
Embedded Linux and Kernel engineering
https://bootlin.com