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SubjectRe: [PATCH] mdio-mux-gpio: Remove VLA usage
On Tue, May 29, 2018 at 03:59:01PM -0700, Kees Cook wrote:
> 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>
> ---
> drivers/net/phy/mdio-mux-gpio.c | 7 ++++++-
> 1 file changed, 6 insertions(+), 1 deletion(-)
>
> diff --git a/drivers/net/phy/mdio-mux-gpio.c b/drivers/net/phy/mdio-mux-gpio.c
> index 082ffef0dec4..e99994f4ed50 100644
> --- a/drivers/net/phy/mdio-mux-gpio.c
> +++ b/drivers/net/phy/mdio-mux-gpio.c
> @@ -26,18 +26,23 @@ 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];
> + int *values;
> unsigned int n;
>
> if (current_child == desired_child)
> return 0;
>
> + values = kmalloc_array(s->gpios->ndescs, sizeof(*values), GFP_KERNEL);
> + if (!values)
> + return -ENOMEM;
> +
> for (n = 0; n < s->gpios->ndescs; n++)
> values[n] = (desired_child >> n) & 1;
>
> gpiod_set_array_value_cansleep(s->gpios->ndescs, s->gpios->desc,
> values);
>
> + kfree(values);
> return 0;
> }

Hi Kees

This is the 'hot path' for this driver, and you are making it more
expensive.

Please allocate the memory once in mdio_mux_gpio_probe and make it
part of mdio_mux_gpio_state.

Thanks
Andrew

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