linux-kernel - [PATCH] Input: gpio_keys - use struct_size() in devm

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Date:   Tue, 18 Jun 2019 10:23:25 -0500
From:   "Gustavo A. R. Silva" <gustavo@...eddedor.com>
To:     Dmitry Torokhov <dmitry.torokhov@...il.com>
Cc:     linux-input@...r.kernel.org, linux-kernel@...r.kernel.org,
        "Gustavo A. R. Silva" <gustavo@...eddedor.com>
Subject: [PATCH] Input: gpio_keys - 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 gpio_keys_drvdata {
	...
        struct gpio_button_data data[0];
};


size = sizeof(struct gpio_keys_drvdata) + count * sizeof(struct gpio_button_data);
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, data, count), GFP_KERNEL);

Notice that, in this case, variable size is not necessary, hence it
is removed.

This code was detected with the help of Coccinelle.

Signed-off-by: Gustavo A. R. Silva <gustavo@...eddedor.com>
---
 drivers/input/keyboard/gpio_keys.c | 6 ++----
 1 file changed, 2 insertions(+), 4 deletions(-)

diff --git a/drivers/input/keyboard/gpio_keys.c b/drivers/input/keyboard/gpio_keys.c
index 6cd199e8a370..c186c2552b04 100644
--- a/drivers/input/keyboard/gpio_keys.c
+++ b/drivers/input/keyboard/gpio_keys.c
@@ -774,7 +774,6 @@ static int gpio_keys_probe(struct platform_device *pdev)
 	struct fwnode_handle *child = NULL;
 	struct gpio_keys_drvdata *ddata;
 	struct input_dev *input;
-	size_t size;
 	int i, error;
 	int wakeup = 0;
 
@@ -784,9 +783,8 @@ static int gpio_keys_probe(struct platform_device *pdev)
 			return PTR_ERR(pdata);
 	}
 
-	size = sizeof(struct gpio_keys_drvdata) +
-			pdata->nbuttons * sizeof(struct gpio_button_data);
-	ddata = devm_kzalloc(dev, size, GFP_KERNEL);
+	ddata = devm_kzalloc(dev, struct_size(ddata, data, pdata->nbuttons),
+			     GFP_KERNEL);
 	if (!ddata) {
 		dev_err(dev, "failed to allocate state\n");
 		return -ENOMEM;
-- 
2.21.0