linux-kernel - Re: [PATCH] Input: uinput - handle compat ioctl for UI_SET

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Message-ID: <20160520163210.GB14951@dtor-ws>
Date:	Fri, 20 May 2016 09:32:10 -0700
From:	Dmitry Torokhov <dmitry.torokhov@...il.com>
To:	Ricky Liang <jcliang@...omium.org>
Cc:	David Herrmann <dh.herrmann@...il.com>,
	Benjamin Tissoires <benjamin.tissoires@...hat.com>,
	Andrew Morton <akpm@...ux-foundation.org>,
	Elias Vanderstuyft <elias.vds@...il.com>,
	Anshul Garg <aksgarg1989@...il.com>,
	"open list:INPUT (KEYBOARD, MOUSE, JOYSTICK, TOUCHSCREEN)..." 
	<linux-input@...r.kernel.org>,
	open list <linux-kernel@...r.kernel.org>
Subject: Re: [PATCH] Input: uinput - handle compat ioctl for UI_SET_PHYS

Hi Ricky,

On Tue, May 17, 2016 at 11:39:45PM +0800, Ricky Liang wrote:
> When running a 32-bit userspace on a 64-bit kernel, the UI_SET_PHYS
> ioctl needs to be treated with special care, as it has the pointer
> size encoded in the command.
> 
> Signed-off-by: Ricky Liang <jcliang@...omium.org>
> ---
>  drivers/input/misc/uinput.c | 9 +++++++++
>  1 file changed, 9 insertions(+)
> 
> diff --git a/drivers/input/misc/uinput.c b/drivers/input/misc/uinput.c
> index abe1a92..b4d1b1d 100644
> --- a/drivers/input/misc/uinput.c
> +++ b/drivers/input/misc/uinput.c
> @@ -984,6 +984,15 @@ static long uinput_ioctl(struct file *file, unsigned int cmd, unsigned long arg)
>  static long uinput_compat_ioctl(struct file *file,
>  				unsigned int cmd, unsigned long arg)
>  {
> +	switch (_IOC_NR(cmd)) {
> +		case _IOC_NR(UI_SET_PHYS):
> +			if (_IOC_SIZE(cmd) == sizeof(compat_uptr_t)) {
> +				cmd &= ~IOCSIZE_MASK;
> +				cmd |= sizeof(void *) << IOCSIZE_SHIFT;
> +			}
> +			break;
> +	}
> +

This looks quite complicated... Can we do this:

#define UI_SET_PHYS_COMPAT __IOW(UINPUT_IOCTL_BASE, 108, compat_uptr_t)

...

	if (cmd == UI_SET_PHYS_COMPAT)
		cmd = UI_SET_PHYS;

>  	return uinput_ioctl_handler(file, cmd, arg, compat_ptr(arg));
>  }
>  #endif

We can use the local define instead of manipulating cmd size because we
will never going to change UI_SET_PHYS definition, since it is part of
uapi.

Thanks.

-- 
Dmitry