linux-kernel - Re: [PATCH v3 8/9] drm/rockchip: gem: Don't alloc/free gem buf when dev_private is invalid

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Message-ID: <58E621D7.3030205@rock-chips.com>
Date:   Thu, 06 Apr 2017 19:09:11 +0800
From:   jeffy <jeffy.chen@...k-chips.com>
To:     Sean Paul <seanpaul@...omium.org>, dianders@...omium.org,
        briannorris@...omium.org, linux-kernel@...r.kernel.org,
        dri-devel@...ts.freedesktop.org, tfiga@...omium.org,
        linux-rockchip@...ts.infradead.org, zyw@...k-chips.com,
        linux-arm-kernel@...ts.infradead.org
Subject: Re: [PATCH v3 8/9] drm/rockchip: gem: Don't alloc/free gem buf when
 dev_private is invalid

Hi Daniel,

On 04/06/2017 04:26 PM, Daniel Vetter wrote:
> On Wed, Apr 05, 2017 at 12:28:40PM -0400, Sean Paul wrote:
>> On Wed, Apr 05, 2017 at 04:29:26PM +0800, Jeffy Chen wrote:
>>> After unbinding drm, the userspace may still has a chance to access
>>> gem buf.
>>>
>>> Add a sanity check for a NULL dev_private to prevent that from
>>> happening.
>>
>> I still don't understand how this is happening. You're saying that these hooks
>> can be called after rockchip_drm_unbind() has finished?
>
> Yeah this is supposed to be impossible. If it isn't, we need to debug and
> fix this properly. This smells like pretty bad duct-tape ...

it looks like after unbind, the user space may still own drm dev fd, and 
could be able to call ioctl:
lrwx------. 1 chronos chronos 64 Mar 15 12:53 28 -> /dev/dri/card1 (deleted)

and the drm_unplug_dev may help it, maybe we should call it in unbind? 
or just break drm_ioctl when drm_dev not registered?

> -Daniel
>
>>
>> Sean
>>
>>>
>>> Signed-off-by: Jeffy Chen <jeffy.chen@...k-chips.com>
>>> ---
>>>
>>> Changes in v3:
>>> Address Daniel Vetter <daniel@...ll.ch>'s comments.
>>> Update commit message.
>>>
>>> Changes in v2: None
>>>
>>>   drivers/gpu/drm/rockchip/rockchip_drm_gem.c | 8 ++++++++
>>>   1 file changed, 8 insertions(+)
>>>
>>> diff --git a/drivers/gpu/drm/rockchip/rockchip_drm_gem.c b/drivers/gpu/drm/rockchip/rockchip_drm_gem.c
>>> index df9e570..205a3dc 100644
>>> --- a/drivers/gpu/drm/rockchip/rockchip_drm_gem.c
>>> +++ b/drivers/gpu/drm/rockchip/rockchip_drm_gem.c
>>> @@ -184,6 +184,9 @@ static int rockchip_gem_alloc_buf(struct rockchip_gem_object *rk_obj,
>>>   	struct drm_device *drm = obj->dev;
>>>   	struct rockchip_drm_private *private = drm->dev_private;
>>>
>>> +	if (!private)
>>> +		return -ENODEV;
>>> +
>>>   	if (private->domain)
>>>   		return rockchip_gem_alloc_iommu(rk_obj, alloc_kmap);
>>>   	else
>>> @@ -208,6 +211,11 @@ static void rockchip_gem_free_dma(struct rockchip_gem_object *rk_obj)
>>>
>>>   static void rockchip_gem_free_buf(struct rockchip_gem_object *rk_obj)
>>>   {
>>> +	struct drm_device *drm = rk_obj->base.dev;
>>> +
>>> +	if (!drm->dev_private)
>>> +		return;
>>> +
>>>   	if (rk_obj->pages)
>>>   		rockchip_gem_free_iommu(rk_obj);
>>>   	else
>>> --
>>> 2.1.4
>>>
>>
>> --
>> Sean Paul, Software Engineer, Google / Chromium OS
>> _______________________________________________
>> dri-devel mailing list
>> dri-devel@...ts.freedesktop.org
>> https://lists.freedesktop.org/mailman/listinfo/dri-devel
>

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