Received-SPF: pass (google.com: best guess record for domain of linux-kernel-owner@vger.kernel.org designates 209.132.180.67 as permitted sender) client-ip=209.132.180.67;
Date:   Tue, 21 Jan 2020 13:02:42 +0000
From:   Russell King - ARM Linux admin <linux@armlinux.org.uk>
To:     Guido =?iso-8859-1?Q?G=FCnther?= <agx@sigxcpu.org>
Cc:     Arnd Bergmann <arnd@arndb.de>,
        Lucas Stach <l.stach@pengutronix.de>,
        Christian Gmeiner <christian.gmeiner@gmail.com>,
        David Airlie <airlied@linux.ie>,
        Daniel Vetter <daniel@ffwll.ch>,
        Philipp Zabel <p.zabel@pengutronix.de>,
        Sam Ravnborg <sam@ravnborg.org>, Rob Herring <robh@kernel.org>,
        Emil Velikov <emil.velikov@collabora.com>,
        etnaviv@lists.freedesktop.org, dri-devel@lists.freedesktop.org,
        linux-kernel@vger.kernel.org
Subject: Re: [PATCH] drm/etnaviv: only reject timeouts with tv_nsec >= 2
 seconds
Message-ID: <20200121130241.GG25745@shell.armlinux.org.uk>
References: <20200121114553.2667556-1-arnd@arndb.de>
 <20200121125546.GA71415@bogon.m.sigxcpu.org>
MIME-Version: 1.0
Content-Type: text/plain; charset=iso-8859-1
Content-Disposition: inline
Content-Transfer-Encoding: 8bit
In-Reply-To: <20200121125546.GA71415@bogon.m.sigxcpu.org>
User-Agent: Mutt/1.10.1 (2018-07-13)
Sender: linux-kernel-owner@vger.kernel.org
Precedence: bulk

On Tue, Jan 21, 2020 at 01:55:46PM +0100, Guido G?nther wrote:
> Hi,
> On Tue, Jan 21, 2020 at 12:45:25PM +0100, Arnd Bergmann wrote:
> > As Guido G?nther reported, get_abs_timeout() in the etnaviv user space
> > sometimes passes timeouts with nanosecond values larger than 1000000000,
> > which gets rejected after my first patch.
> > 
> > To avoid breaking this, while also not allowing completely arbitrary
> > values, set the limit to 1999999999 and use set_normalized_timespec64()
> > to get the correct format before comparing it.
> 
> I'm seeing values up to 5 seconds so I need
> 
>      if (args->timeout.tv_nsec > (5 * NSEC_PER_SEC))

I assume you're looking at 64-bit, but I suspect userspace needs
looking at considering 32-bit.  If userspace uses a 32-bit tv_nsec
anywhere in the path that it attempts to pass up to 5 seconds in
tv_nsec, then this will fail to pass the correct timeout.

If that is the case, userspace is buggy, and needs fixing not to
pass such large values through tv_nsec irrespective of this issue.

-- 
RMK's Patch system: https://www.armlinux.org.uk/developer/patches/
FTTC broadband for 0.8mile line in suburbia: sync at 12.1Mbps down 622kbps up
According to speedtest.net: 11.9Mbps down 500kbps up