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Subject: Re: [PATCHv2 4/4] gpio: Remove VLA from stmpe driver
To:     Laura Abbott <labbott@redhat.com>,
        Linus Walleij <linus.walleij@linaro.org>,
        Kees Cook <keescook@chromium.org>,
        Patrice Chotard <patrice.chotard@st.com>
Cc:     linux-gpio@vger.kernel.org, linux-kernel@vger.kernel.org,
        kernel-hardening@lists.openwall.com
References: <20180315180030.20001-1-labbott@redhat.com>
 <20180315180030.20001-5-labbott@redhat.com>
From:   Phil Reid <preid@electromag.com.au>
Message-ID: <21a2e869-62fb-75ef-ae7b-a27e136696f7@electromag.com.au>
Date:   Mon, 19 Mar 2018 09:29:59 +0800
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On 16/03/2018 02:00, Laura Abbott wrote:
> The new challenge is to remove VLAs from the kernel
> (see https://lkml.org/lkml/2018/3/7/621)
> 
> This patch replaces a VLA with an appropriate call to kmalloc_array.
> 
> Signed-off-by: Laura Abbott <labbott@redhat.com>
> ---
> v2: Switch to GFP_KERNEL. There was some discussion about if we should
> be doing the allocation at all but given a) the allocation is pretty
> small and b) we can possibly take a mutex in a called function I think
> this is fine.

I still think it's a bad idea. It's simple to preallocate the buffer.
But it's up to the maintainer.


> ---
>   drivers/gpio/gpio-stmpe.c | 7 ++++++-
>   1 file changed, 6 insertions(+), 1 deletion(-)
> 
> diff --git a/drivers/gpio/gpio-stmpe.c b/drivers/gpio/gpio-stmpe.c
> index f8d7d1cd8488..c2bb20ace6f5 100644
> --- a/drivers/gpio/gpio-stmpe.c
> +++ b/drivers/gpio/gpio-stmpe.c
> @@ -369,10 +369,14 @@ static irqreturn_t stmpe_gpio_irq(int irq, void *dev)
>   	struct stmpe *stmpe = stmpe_gpio->stmpe;
>   	u8 statmsbreg;
>   	int num_banks = DIV_ROUND_UP(stmpe->num_gpios, 8);
> -	u8 status[num_banks];
> +	u8 *status;
>   	int ret;
>   	int i;
>   
> +	status = kmalloc_array(num_banks, sizeof(*status), GFP_KERNEL);
> +	if (!status)
> +		return IRQ_NONE;
> +
>   	/*
>   	 * the stmpe_block_read() call below, imposes to set statmsbreg
>   	 * with the register located at the lowest address. As STMPE1600
> @@ -424,6 +428,7 @@ static irqreturn_t stmpe_gpio_irq(int irq, void *dev)
>   		}
>   	}
>   
> +	kfree(status);
>   	return IRQ_HANDLED;
>   }
>   
> 


-- 
Regards
Phil Reid