[PATCH v4 net-next] mdio-mux-gpio: Remove VLA usage

[PATCH v4 net-next] mdio-mux-gpio: Remove VLA usage

[Kees Cook]

In the quest to remove all stack VLA usage from the kernel[1], this
allocates the values buffer during the callback instead of putting it
on the stack.

[1] https://lkml.kernel.org/r/CA+55aFzCG-zNmZwX4A2FQpadafLfEzK6CC=qPXydAacU1RqZWA@mail.gmail.com

Signed-off-by: Kees Cook <keescook@chromium.org>
Reviewed-by: Andrew Lunn <andrew@lunn.ch>
---
v4: use struct_size() helper for allocation (Joe Perches)
v3: resend to netdev with Reviewed-by
v2: allocate array as part of structure (Andrew Lunn)
---
 drivers/net/phy/mdio-mux-gpio.c | 22 ++++++++++++++--------
 1 file changed, 14 insertions(+), 8 deletions(-)

diff --git a/drivers/net/phy/mdio-mux-gpio.c b/drivers/net/phy/mdio-mux-gpio.c
index 082ffef0dec4..bc90764a8b8d 100644
--- a/drivers/net/phy/mdio-mux-gpio.c
+++ b/drivers/net/phy/mdio-mux-gpio.c
@@ -20,23 +20,23 @@
 struct mdio_mux_gpio_state {
 	struct gpio_descs *gpios;
 	void *mux_handle;
+	int values[];
 };
 
 static int mdio_mux_gpio_switch_fn(int current_child, int desired_child,
 				   void *data)
 {
 	struct mdio_mux_gpio_state *s = data;
-	int values[s->gpios->ndescs];
 	unsigned int n;
 
 	if (current_child == desired_child)
 		return 0;
 
 	for (n = 0; n < s->gpios->ndescs; n++)
-		values[n] = (desired_child >> n) & 1;
+		s->values[n] = (desired_child >> n) & 1;
 
 	gpiod_set_array_value_cansleep(s->gpios->ndescs, s->gpios->desc,
-				       values);
+				       s->values);
 
 	return 0;
 }
@@ -44,15 +44,21 @@ static int mdio_mux_gpio_switch_fn(int current_child, int desired_child,
 static int mdio_mux_gpio_probe(struct platform_device *pdev)
 {
 	struct mdio_mux_gpio_state *s;
+	struct gpio_descs *gpios;
 	int r;
 
-	s = devm_kzalloc(&pdev->dev, sizeof(*s), GFP_KERNEL);
-	if (!s)
+	gpios = gpiod_get_array(&pdev->dev, NULL, GPIOD_OUT_LOW);
+	if (IS_ERR(gpios))
+		return PTR_ERR(gpios);
+
+	s = devm_kzalloc(&pdev->dev, struct_size(s, values, gpios->ndescs),
+			 GFP_KERNEL);
+	if (!s) {
+		gpiod_put_array(gpios);
 		return -ENOMEM;
+	}
 
-	s->gpios = gpiod_get_array(&pdev->dev, NULL, GPIOD_OUT_LOW);
-	if (IS_ERR(s->gpios))
-		return PTR_ERR(s->gpios);
+	s->gpios = gpios;
 
 	r = mdio_mux_init(&pdev->dev, pdev->dev.of_node,
 			  mdio_mux_gpio_switch_fn, &s->mux_handle, s, NULL);
-- 
2.17.1


-- 
Kees Cook
Pixel Security

Re: [PATCH v4 net-next] mdio-mux-gpio: Remove VLA usage

[David Miller]

From: Kees Cook <keescook@chromium.org>
Date: Mon, 25 Jun 2018 15:49:49 -0700

> In the quest to remove all stack VLA usage from the kernel[1], this
> allocates the values buffer during the callback instead of putting it
> on the stack.
> 
> [1] https://lkml.kernel.org/r/CA+55aFzCG-zNmZwX4A2FQpadafLfEzK6CC=qPXydAacU1RqZWA@mail.gmail.com
> 
> Signed-off-by: Kees Cook <keescook@chromium.org>
> Reviewed-by: Andrew Lunn <andrew@lunn.ch>

Applied.