linux-kernel - Re: [PATCH 8/8] Input: input_event: fix struct padding on sparc64

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Date:   Mon, 11 Nov 2019 10:28:28 -0800
From:   Dmitry Torokhov <dmitry.torokhov@...il.com>
To:     Arnd Bergmann <arnd@...db.de>
Cc:     y2038@...ts.linaro.org, linux-kernel@...r.kernel.org,
        sparclinux@...r.kernel.org,
        "David S. Miller" <davem@...emloft.net>, stable@...r.kernel.org,
        Deepa Dinamani <deepa.kernel@...il.com>,
        Thomas Gleixner <tglx@...utronix.de>,
        linux-input@...r.kernel.org
Subject: Re: [PATCH 8/8] Input: input_event: fix struct padding on sparc64

Hi Arnd,

On Fri, Nov 08, 2019 at 09:34:31PM +0100, Arnd Bergmann wrote:
> Going through all uses of timeval, I noticed that we screwed up
> input_event in the previous attempts to fix it:
> 
> The time fields now match between kernel and user space, but
> all following fields are in the wrong place.
> 
> Add the required padding that is implied by the glibc timeval
> definition to fix the layout, and add explicit initialization
> to avoid leaking kernel stack data.
> 
> Cc: sparclinux@...r.kernel.org
> Cc: "David S. Miller" <davem@...emloft.net>
> Cc: stable@...r.kernel.org
> Fixes: 141e5dcaa735 ("Input: input_event - fix the CONFIG_SPARC64 mixup")
> Fixes: 2e746942ebac ("Input: input_event - provide override for sparc64")
> Signed-off-by: Arnd Bergmann <arnd@...db.de>
> ---
>  drivers/input/evdev.c       | 3 +++
>  drivers/input/misc/uinput.c | 3 +++
>  include/uapi/linux/input.h  | 1 +
>  3 files changed, 7 insertions(+)
> 
> diff --git a/drivers/input/evdev.c b/drivers/input/evdev.c
> index d7dd6fcf2db0..24a90793caf0 100644
> --- a/drivers/input/evdev.c
> +++ b/drivers/input/evdev.c
> @@ -228,6 +228,9 @@ static void __pass_event(struct evdev_client *client,
>  						event->input_event_sec;
>  		client->buffer[client->tail].input_event_usec =
>  						event->input_event_usec;
> +#ifdef CONFIG_SPARC64
> +		client->buffer[client->tail].__pad = 0;
> +#endif
>  		client->buffer[client->tail].type = EV_SYN;
>  		client->buffer[client->tail].code = SYN_DROPPED;
>  		client->buffer[client->tail].value = 0;

I do not like ifdefs here, do you think we could write:

		client->buffer[client->tail] = (struct input_event) {
			.input_event_sec = event->input_event_sec,
			.input_event_usec = event->input_event_usec,
			.type = EV_SYN,
			.code = SYN_DROPPED,
		};

to ensure all padded fields are initialized? This is not hot path as we
do not expect queue to overfill too often.

Thanks.

-- 
Dmitry