linux-kernel - Re: [PATCH v2] mtd: sa1100: avoid VLA in sa1100_setup

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Date:   Mon, 5 Nov 2018 09:11:24 +0100
From:   Boris Brezillon <boris.brezillon@...tlin.com>
To:     David Woodhouse <dwmw2@...radead.org>,
        Brian Norris <computersforpeace@...il.com>,
        Boris Brezillon <boris.brezillon@...tlin.com>,
        Marek Vasut <marek.vasut@...il.com>,
        Richard Weinberger <richard@....at>,
        linux-mtd@...ts.infradead.org
Cc:     linux-kernel@...r.kernel.org, Kees Cook <keescook@...omium.org>,
        Olof Johansson <olof@...om.net>
Subject: Re: [PATCH v2] mtd: sa1100: avoid VLA in sa1100_setup_mtd

On Mon,  5 Nov 2018 08:58:35 +0100
Boris Brezillon <boris.brezillon@...tlin.com> wrote:

> Enabling -Wvla found another variable-length array with randconfig
> testing:
> 
> drivers/mtd/maps/sa1100-flash.c: In function 'sa1100_setup_mtd':
> drivers/mtd/maps/sa1100-flash.c:224:10: error: ISO C90 forbids variable length array 'cdev' [-Werror=vla]
> 
> Dynamically allocate the cdev array passed to mtd_concat_create()
> instead of using a VLA.
> 
> Reported-by: Arnd Bergmann <arnd@...db.de>
> Signed-off-by: Boris Brezillon <boris.brezillon@...tlin.com>
> Cc: Kees Cook <keescook@...omium.org>
> Cc: Olof Johansson <olof@...om.net>
> ---
> Changes in v2:
> - Allocate cdev dynamically instead of having a fixed-size array
> 
> Hello,
> 
> I'm planning to queue this patch to the mtd/fixes PR. Arnd, Kees, feel

						    ^ I meant branch,
not PR, but this patch should also be part of the 4.20-rc2 fixes PR.

> free to add your R-b.
> 
> Regards,
> 
> Boris
> ---
>  drivers/mtd/maps/sa1100-flash.c | 10 +++++++++-
>  1 file changed, 9 insertions(+), 1 deletion(-)
> 
> diff --git a/drivers/mtd/maps/sa1100-flash.c b/drivers/mtd/maps/sa1100-flash.c
> index 784c6e1a0391..fd5fe12d7461 100644
> --- a/drivers/mtd/maps/sa1100-flash.c
> +++ b/drivers/mtd/maps/sa1100-flash.c
> @@ -221,7 +221,14 @@ static struct sa_info *sa1100_setup_mtd(struct platform_device *pdev,
>  		info->mtd = info->subdev[0].mtd;
>  		ret = 0;
>  	} else if (info->num_subdev > 1) {
> -		struct mtd_info *cdev[nr];
> +		struct mtd_info **cdev;
> +
> +		cdev = kmalloc_array(nr, sizeof(*cdev), GFP_KERNEL);
> +		if (!cdev) {
> +			ret = -ENOMEM;
> +			goto err;
> +		}
> +
>  		/*
>  		 * We detected multiple devices.  Concatenate them together.
>  		 */
> @@ -230,6 +237,7 @@ static struct sa_info *sa1100_setup_mtd(struct platform_device *pdev,
>  
>  		info->mtd = mtd_concat_create(cdev, info->num_subdev,
>  					      plat->name);
> +		kfree(cdev);
>  		if (info->mtd == NULL) {
>  			ret = -ENXIO;
>  			goto err;