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Date: Thu, 25 May 2017 22:52:18 -0700
From: Christoph Hellwig <hch@infradead.org>
To: jeffy <jeffy.chen@rock-chips.com>
Cc: Sean Paul <seanpaul@chromium.org>, linux-kernel@vger.kernel.org,
        tfiga@chromium.org, Mark Yao <mark.yao@rock-chips.com>,
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Subject: Re: [PATCH] drm/rockchip: Don't allow zero sized gem buffer
Message-ID: <20170526055218.GA23802@infradead.org>
References: <1495521583-29151-1-git-send-email-jeffy.chen@rock-chips.com>
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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.