linux-kernel - Re: [PATCH V4 2/2] Move stack parameters for sed_ioctl to prevent oversized stack with CONFIG

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Message-ID: <20170213075422.GB20361@infradead.org>
Date:   Sun, 12 Feb 2017 23:54:22 -0800
From:   Christoph Hellwig <hch@...radead.org>
To:     Scott Bauer <scott.bauer@...el.com>
Cc:     linux-nvme@...ts.infradead.org, David.Laight@...LAB.COM,
        arnd@...db.de, axboe@...com, keith.busch@...el.com,
        jonathan.derrick@...el.com, hch@...radead.org,
        linux-kernel@...r.kernel.org, linux-block@...r.kernel.org
Subject: Re: [PATCH V4 2/2] Move stack parameters for sed_ioctl to prevent
 oversized stack with CONFIG_KASAN

>  int sed_ioctl(struct opal_dev *dev, unsigned int cmd, unsigned long ptr)
>  {
> +	void *ioctl_ptr;
> +	int ret = -ENOTTY;
>  	void __user *arg = (void __user *)ptr;

Can we use this opportunity to clean up the usual ioctl argument mess.
Id say pass the "void __user *argp" argument already (nvme_ioctl should
have a local variable for it anyway), and then just rename ioctl_ptr
variable to the usual short p.

> +	unsigned int cmd_size = _IOC_SIZE(cmd);
>  

> +	ioctl_ptr = memdup_user(arg, cmd_size);

cmd_size is only used once, so why not opencode the expression in the
argument to memdup_user.