linux-kernel - Re: [Y2038] [PATCH v2 13/24] drm/etnaviv: reject timeouts with tv_nsec >= NSEC_PER

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Date:   Wed, 08 Jan 2020 01:16:09 +0000
From:   Ben Hutchings <ben.hutchings@...ethink.co.uk>
To:     Arnd Bergmann <arnd@...db.de>, y2038@...ts.linaro.org,
        linux-kernel@...r.kernel.org, Lucas Stach <l.stach@...gutronix.de>,
        David Airlie <airlied@...ux.ie>,
        Daniel Vetter <daniel@...ll.ch>
Cc:     Guido Günther <agx@...xcpu.org>,
        etnaviv@...ts.freedesktop.org, dri-devel@...ts.freedesktop.org,
        Christian Gmeiner <christian.gmeiner@...il.com>,
        Philipp Zabel <p.zabel@...gutronix.de>,
        Russell King <linux+etnaviv@...linux.org.uk>,
        Sam Ravnborg <sam@...nborg.org>,
        Emil Velikov <emil.velikov@...labora.com>
Subject: Re: [Y2038] [PATCH v2 13/24] drm/etnaviv: reject timeouts with
 tv_nsec >= NSEC_PER_SEC

On Fri, 2019-12-13 at 21:53 +0100, Arnd Bergmann wrote:
> Most kernel interfaces that take a timespec require normalized
> representation with tv_nsec between 0 and NSEC_PER_SEC.
> 
> Passing values larger than 0x100000000ull further behaves differently
> on 32-bit and 64-bit kernels, and can cause the latter to spend a long
> time counting seconds in timespec64_sub()/set_normalized_timespec64().
> 
> Reject those large values at the user interface to enforce sane and
> portable behavior.
> 
> Signed-off-by: Arnd Bergmann <arnd@...db.de>
> ---
>  drivers/gpu/drm/etnaviv/etnaviv_drv.c | 9 +++++++++
>  1 file changed, 9 insertions(+)
> 
> diff --git a/drivers/gpu/drm/etnaviv/etnaviv_drv.c b/drivers/gpu/drm/etnaviv/etnaviv_drv.c
> index 1f9c01be40d7..95d72dc00280 100644
> --- a/drivers/gpu/drm/etnaviv/etnaviv_drv.c
> +++ b/drivers/gpu/drm/etnaviv/etnaviv_drv.c
> @@ -297,6 +297,9 @@ static int etnaviv_ioctl_gem_cpu_prep(struct drm_device *dev, void *data,
>  	if (args->op & ~(ETNA_PREP_READ | ETNA_PREP_WRITE | ETNA_PREP_NOSYNC))
>  		return -EINVAL;
>  
> +	if (args->timeout.tv_nsec > NSEC_PER_SEC)
[...]

There's an off-by-one error between the subject line and the actual
changes.  The subject line seems to have the correct comparison.

Ben.

-- 
Ben Hutchings, Software Developer                         Codethink Ltd
https://www.codethink.co.uk/                 Dale House, 35 Dale Street
                                     Manchester, M1 2HF, United Kingdom