linux-kernel - Re: [PATCH] drm/rockchip: Don't allow zero sized gem buffer

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Date:   Thu, 25 May 2017 22:52:18 -0700
From:   Christoph Hellwig <hch@...radead.org>
To:     jeffy <jeffy.chen@...k-chips.com>
Cc:     Sean Paul <seanpaul@...omium.org>, linux-kernel@...r.kernel.org,
        tfiga@...omium.org, Mark Yao <mark.yao@...k-chips.com>,
        Heiko Stuebner <heiko@...ech.de>,
        dri-devel@...ts.freedesktop.org,
        linux-rockchip@...ts.infradead.org,
        David Airlie <airlied@...ux.ie>,
        linux-arm-kernel@...ts.infradead.org
Subject: Re: [PATCH] drm/rockchip: Don't allow zero sized gem buffer

On Fri, May 26, 2017 at 10:30:09AM +0800, jeffy wrote:
> Hi sean,
> 
> On 05/25/2017 11:30 PM, Sean Paul wrote:
> > On Tue, May 23, 2017 at 02:39:43PM +0800, Jeffy Chen wrote:
> > > The system would crash when trying to alloc zero sized gem buffer:
> > > [    6.712435] Unable to handle kernel NULL pointer dereference at virtual address 00000010 <--ZERO_SIZE_PTR
> > > ...
> > > [    6.757502] PC is at sg_alloc_table_from_pages+0x170/0x1ec
> > 
> > It's unfortunate that you didn't include the entire stack trace. From code
> > inspection, it seems like the 0 size comes from the fb_probe path? Is there
> > somewhere in the helpers that you could check the mode is sane so all drivers
> > can benefit?
> 
> hmm, sorry, i was testing it on chromeos 4.4 kernel, it turns out that we
> have a custom ioctl for userspace to create gem buffer(the same as exynos
> drm), which might get the the 0 size.
> 
> but on upstream kernel, it could only be called by dump_create, and the
> drm_mode_create_dumb_ioctl already did the size check.
> 
> will resent this patch, and rewrite the commit message, thanx.

That suggests that this patch isn't needed at all.