linux-kernel - Re: [RFC v3 6/9] kmsg: add ioctl for adding and deleting kmsg* devices

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Date:	Mon, 19 Oct 2015 15:19:25 +0200
From:	Arnd Bergmann <arnd@...db.de>
To:	Paul Osmialowski <p.osmialowsk@...sung.com>
Cc:	Jonathan Corbet <corbet@....net>,
	Andrew Morton <akpm@...ux-foundation.org>,
	Petr Mladek <pmladek@...e.cz>,
	Greg Kroah-Hartman <gregkh@...uxfoundation.org>,
	Daniel Mack <daniel@...que.org>,
	Kay Sievers <kay.sievers@...y.org>,
	Joe Perches <joe@...ches.com>, Tejun Heo <tj@...nel.org>,
	linux-kernel@...r.kernel.org, linux-doc@...r.kernel.org,
	linux-api@...r.kernel.org,
	Marcin Niesluchowski <m.niesluchow@...sung.com>,
	Karol Lewandowski <k.lewandowsk@...sung.com>,
	Bartlomiej Zolnierkiewicz <b.zolnierkie@...sung.com>,
	Shuah Khan <shuahkh@....samsung.com>
Subject: Re: [RFC v3 6/9] kmsg: add ioctl for adding and deleting kmsg* devices

On Monday 19 October 2015 14:58:20 Paul Osmialowski wrote:
> +
> +struct kmsg_cmd_buffer_add {
> +       size_t size;
> +       unsigned short mode;
> +       int minor;
> +} __attribute__((packed));
> +
> +#define KMSG_IOCTL_MAGIC       0xBB
> +
> +/*
> 

Try to avoid using packed unaligned data structures. Here I would
just use __u64 and __u32 members.

> +       case KMSG_CMD_BUFFER_ADD:
> +               if (copy_from_user(&size, argp, sizeof(size)))
> +                       return -EFAULT;
> +               argp += sizeof(size);
> +               if (copy_from_user(&mode, argp, sizeof(mode)))
> +                       return -EFAULT;

This is a rather unusual way to access the data. Just copy the
entire structure to the stack.

	Arnd
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