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

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Message-ID: <20170526134949.z4dp4zsgipmbgdl3@art_vandelay>
Date:   Fri, 26 May 2017 09:49:49 -0400
From:   Sean Paul <seanpaul@...omium.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.

Ah, ok. In that case, fix the custom ioctl such that it ensures we never call
this function with size == 0, and upload it downstream with a CHROMIUM prefix.

Sean


> 
> will resent this patch, and rewrite the commit message, thanx.
> 
> > 
> > Sean
> > 
> > > 
> > > Signed-off-by: Jeffy Chen <jeffy.chen@...k-chips.com>
> > > ---
> > > 
> > >   drivers/gpu/drm/rockchip/rockchip_drm_gem.c | 5 +++++
> > >   1 file changed, 5 insertions(+)
> > > 
> > > diff --git a/drivers/gpu/drm/rockchip/rockchip_drm_gem.c b/drivers/gpu/drm/rockchip/rockchip_drm_gem.c
> > > index df9e570..8917922 100644
> > > --- a/drivers/gpu/drm/rockchip/rockchip_drm_gem.c
> > > +++ b/drivers/gpu/drm/rockchip/rockchip_drm_gem.c
> > > @@ -315,6 +315,11 @@ struct rockchip_gem_object *
> > >   	struct drm_gem_object *obj;
> > >   	int ret;
> > > 
> > > +	if (!size) {
> > > +		DRM_ERROR("gem buffer size is zero\n");
> > > +		return ERR_PTR(-EINVAL);
> > > +	}
> > > +
> > >   	size = round_up(size, PAGE_SIZE);
> > > 
> > >   	rk_obj = kzalloc(sizeof(*rk_obj), GFP_KERNEL);
> > > --
> > > 2.1.4
> > > 
> > 
> 

-- 
Sean Paul, Software Engineer, Google / Chromium OS