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

[jeffy]

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.

> Sean
>
> > Signed-off-by: Jeffy Chen <jeffy.chen@xxxxxxxxxxxxxx>
> > ---
> >
> >   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