[PATCH] drm/kmb: fix dereference before NULL check in kmb_plane_atomic_update()

[PATCH] drm/kmb: fix dereference before NULL check in kmb_plane_atomic_update()

[Zeng Jingxiang]

From: Zeng Jingxiang <linuszeng@tencent.com>

The "plane" pointer was access before checking if it was NULL.

The drm_atomic_get_old_plane_state() function will dereference
the pointer "plane".
345	struct drm_plane_state *old_plane_state =
		drm_atomic_get_old_plane_state(state, plane);
346	struct drm_plane_state *new_plane_state =
		drm_atomic_get_new_plane_state(state, plane);

A NULL check for "plane" indicates that it may be NULL
363	if (!plane || !new_plane_state || !old_plane_state)

Fixes: 977697e20b3d ("drm/atomic: Pass the full state to planes atomic disable and update")
Fixes: 37418bf14c13 ("drm: Use state helper instead of the plane state pointer")
Signed-off-by: Zeng Jingxiang <linuszeng@tencent.com>
---
 drivers/gpu/drm/kmb/kmb_plane.c | 13 ++++++++-----
 1 file changed, 8 insertions(+), 5 deletions(-)

diff --git a/drivers/gpu/drm/kmb/kmb_plane.c b/drivers/gpu/drm/kmb/kmb_plane.c
index 2735b8eb3537..d2bc998b65ce 100644
--- a/drivers/gpu/drm/kmb/kmb_plane.c
+++ b/drivers/gpu/drm/kmb/kmb_plane.c
@@ -342,10 +342,7 @@ static void kmb_plane_set_alpha(struct kmb_drm_private *kmb,
 static void kmb_plane_atomic_update(struct drm_plane *plane,
 				    struct drm_atomic_state *state)
 {
-	struct drm_plane_state *old_plane_state = drm_atomic_get_old_plane_state(state,
-										 plane);
-	struct drm_plane_state *new_plane_state = drm_atomic_get_new_plane_state(state,
-										 plane);
+	struct drm_plane_state *old_plane_state, *new_plane_state;
 	struct drm_framebuffer *fb;
 	struct kmb_drm_private *kmb;
 	unsigned int width;
@@ -360,7 +357,13 @@ static void kmb_plane_atomic_update(struct drm_plane *plane,
 	static dma_addr_t addr[MAX_SUB_PLANES];
 	struct disp_cfg *init_disp_cfg;
 
-	if (!plane || !new_plane_state || !old_plane_state)
+	if (!plane)
+		return;
+
+	old_plane_state = drm_atomic_get_old_plane_state(state, plane);
+	new_plane_state = drm_atomic_get_new_plane_state(state, plane);
+
+	if (!new_plane_state || !old_plane_state)
 		return;
 
 	fb = new_plane_state->fb;
-- 
2.27.0

Re: [PATCH] drm/kmb: fix dereference before NULL check in kmb_plane_atomic_update()

[Thomas Zimmermann]

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Hi

Am 29.07.22 um 05:07 schrieb Zeng Jingxiang:
> From: Zeng Jingxiang <linuszeng@tencent.com>
> 
> The "plane" pointer was access before checking if it was NULL.
> 
> The drm_atomic_get_old_plane_state() function will dereference
> the pointer "plane".
> 345	struct drm_plane_state *old_plane_state =
> 		drm_atomic_get_old_plane_state(state, plane);
> 346	struct drm_plane_state *new_plane_state =
> 		drm_atomic_get_new_plane_state(state, plane);
> 
> A NULL check for "plane" indicates that it may be NULL
> 363	if (!plane || !new_plane_state || !old_plane_state)

Is this an actual bug that happens?

All planes should always have a state. Therefore the tests for 
!new_plane_state and !old_plane_state can be removed, I'd say.

Best regards
Thomas

> 
> Fixes: 977697e20b3d ("drm/atomic: Pass the full state to planes atomic disable and update")
> Fixes: 37418bf14c13 ("drm: Use state helper instead of the plane state pointer")
> Signed-off-by: Zeng Jingxiang <linuszeng@tencent.com>
> ---
>   drivers/gpu/drm/kmb/kmb_plane.c | 13 ++++++++-----
>   1 file changed, 8 insertions(+), 5 deletions(-)
> 
> diff --git a/drivers/gpu/drm/kmb/kmb_plane.c b/drivers/gpu/drm/kmb/kmb_plane.c
> index 2735b8eb3537..d2bc998b65ce 100644
> --- a/drivers/gpu/drm/kmb/kmb_plane.c
> +++ b/drivers/gpu/drm/kmb/kmb_plane.c
> @@ -342,10 +342,7 @@ static void kmb_plane_set_alpha(struct kmb_drm_private *kmb,
>   static void kmb_plane_atomic_update(struct drm_plane *plane,
>   				    struct drm_atomic_state *state)
>   {
> -	struct drm_plane_state *old_plane_state = drm_atomic_get_old_plane_state(state,
> -										 plane);
> -	struct drm_plane_state *new_plane_state = drm_atomic_get_new_plane_state(state,
> -										 plane);
> +	struct drm_plane_state *old_plane_state, *new_plane_state;
>   	struct drm_framebuffer *fb;
>   	struct kmb_drm_private *kmb;
>   	unsigned int width;
> @@ -360,7 +357,13 @@ static void kmb_plane_atomic_update(struct drm_plane *plane,
>   	static dma_addr_t addr[MAX_SUB_PLANES];
>   	struct disp_cfg *init_disp_cfg;
>   
> -	if (!plane || !new_plane_state || !old_plane_state)
> +	if (!plane)
> +		return;
> +
> +	old_plane_state = drm_atomic_get_old_plane_state(state, plane);
> +	new_plane_state = drm_atomic_get_new_plane_state(state, plane);
> +
> +	if (!new_plane_state || !old_plane_state)
>   		return;
>   
>   	fb = new_plane_state->fb;

-- 
Thomas Zimmermann
Graphics Driver Developer
SUSE Software Solutions Germany GmbH
Maxfeldstr. 5, 90409 Nürnberg, Germany
(HRB 36809, AG Nürnberg)
Geschäftsführer: Ivo Totev

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Re: [PATCH] drm/kmb: fix dereference before NULL check in kmb_plane_atomic_update()

[Thomas Zimmermann]

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Hi

Am 29.07.22 um 16:23 schrieb Thomas Zimmermann:
> Hi
> 
> Am 29.07.22 um 05:07 schrieb Zeng Jingxiang:
>> From: Zeng Jingxiang <linuszeng@tencent.com>
>>
>> The "plane" pointer was access before checking if it was NULL.
>>
>> The drm_atomic_get_old_plane_state() function will dereference
>> the pointer "plane".
>> 345    struct drm_plane_state *old_plane_state =
>>         drm_atomic_get_old_plane_state(state, plane);
>> 346    struct drm_plane_state *new_plane_state =
>>         drm_atomic_get_new_plane_state(state, plane);
>>
>> A NULL check for "plane" indicates that it may be NULL
>> 363    if (!plane || !new_plane_state || !old_plane_state)
> 
> Is this an actual bug that happens?
> 
> All planes should always have a state. Therefore the tests for 
> !new_plane_state and !old_plane_state can be removed, I'd say.

Just to clarify: moving the test for !plane before using one of the 
get_plane_state functions is a correct bugfix.

Best regards
Thomas

> 
> Best regards
> Thomas
> 
>>
>> Fixes: 977697e20b3d ("drm/atomic: Pass the full state to planes atomic 
>> disable and update")
>> Fixes: 37418bf14c13 ("drm: Use state helper instead of the plane state 
>> pointer")
>> Signed-off-by: Zeng Jingxiang <linuszeng@tencent.com>
>> ---
>>   drivers/gpu/drm/kmb/kmb_plane.c | 13 ++++++++-----
>>   1 file changed, 8 insertions(+), 5 deletions(-)
>>
>> diff --git a/drivers/gpu/drm/kmb/kmb_plane.c 
>> b/drivers/gpu/drm/kmb/kmb_plane.c
>> index 2735b8eb3537..d2bc998b65ce 100644
>> --- a/drivers/gpu/drm/kmb/kmb_plane.c
>> +++ b/drivers/gpu/drm/kmb/kmb_plane.c
>> @@ -342,10 +342,7 @@ static void kmb_plane_set_alpha(struct 
>> kmb_drm_private *kmb,
>>   static void kmb_plane_atomic_update(struct drm_plane *plane,
>>                       struct drm_atomic_state *state)
>>   {
>> -    struct drm_plane_state *old_plane_state = 
>> drm_atomic_get_old_plane_state(state,
>> -                                         plane);
>> -    struct drm_plane_state *new_plane_state = 
>> drm_atomic_get_new_plane_state(state,
>> -                                         plane);
>> +    struct drm_plane_state *old_plane_state, *new_plane_state;
>>       struct drm_framebuffer *fb;
>>       struct kmb_drm_private *kmb;
>>       unsigned int width;
>> @@ -360,7 +357,13 @@ static void kmb_plane_atomic_update(struct 
>> drm_plane *plane,
>>       static dma_addr_t addr[MAX_SUB_PLANES];
>>       struct disp_cfg *init_disp_cfg;
>> -    if (!plane || !new_plane_state || !old_plane_state)
>> +    if (!plane)
>> +        return;
>> +
>> +    old_plane_state = drm_atomic_get_old_plane_state(state, plane);
>> +    new_plane_state = drm_atomic_get_new_plane_state(state, plane);
>> +
>> +    if (!new_plane_state || !old_plane_state)
>>           return;
>>       fb = new_plane_state->fb;
> 

-- 
Thomas Zimmermann
Graphics Driver Developer
SUSE Software Solutions Germany GmbH
Maxfeldstr. 5, 90409 Nürnberg, Germany
(HRB 36809, AG Nürnberg)
Geschäftsführer: Ivo Totev

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RE: [PATCH] drm/kmb: fix dereference before NULL check in kmb_plane_atomic_update()

[Chrisanthus, Anitha]

Agree with Thomas, drm_atomic_commit() will not call kmb_atomic_update() with a NULL plane. This is not an actual bug.

Thanks,
Anitha 

> -----Original Message-----
> From: Thomas Zimmermann <tzimmermann@suse.de>
> Sent: Friday, July 29, 2022 7:26 AM
> To: Zeng Jingxiang <zengjx95@gmail.com>; Chrisanthus, Anitha
> <anitha.chrisanthus@intel.com>; edmund.j.dea@intel.com; airlied@linux.ie;
> daniel@ffwll.ch; laurent.pinchart@ideasonboard.com; maxime@cerno.tech;
> ville.syrjala@linux.intel.com
> Cc: Zeng Jingxiang <linuszeng@tencent.com>; linux-kernel@vger.kernel.org;
> dri-devel@lists.freedesktop.org
> Subject: Re: [PATCH] drm/kmb: fix dereference before NULL check in
> kmb_plane_atomic_update()
> 
> Hi
> 
> Am 29.07.22 um 16:23 schrieb Thomas Zimmermann:
> > Hi
> >
> > Am 29.07.22 um 05:07 schrieb Zeng Jingxiang:
> >> From: Zeng Jingxiang <linuszeng@tencent.com>
> >>
> >> The "plane" pointer was access before checking if it was NULL.
> >>
> >> The drm_atomic_get_old_plane_state() function will dereference
> >> the pointer "plane".
> >> 345    struct drm_plane_state *old_plane_state =
> >>         drm_atomic_get_old_plane_state(state, plane);
> >> 346    struct drm_plane_state *new_plane_state =
> >>         drm_atomic_get_new_plane_state(state, plane);
> >>
> >> A NULL check for "plane" indicates that it may be NULL
> >> 363    if (!plane || !new_plane_state || !old_plane_state)
> >
> > Is this an actual bug that happens?
> >
> > All planes should always have a state. Therefore the tests for
> > !new_plane_state and !old_plane_state can be removed, I'd say.
> 
> Just to clarify: moving the test for !plane before using one of the
> get_plane_state functions is a correct bugfix.
> 
> Best regards
> Thomas
> 
> >
> > Best regards
> > Thomas
> >
> >>
> >> Fixes: 977697e20b3d ("drm/atomic: Pass the full state to planes atomic
> >> disable and update")
> >> Fixes: 37418bf14c13 ("drm: Use state helper instead of the plane state
> >> pointer")
> >> Signed-off-by: Zeng Jingxiang <linuszeng@tencent.com>
> >> ---
> >>   drivers/gpu/drm/kmb/kmb_plane.c | 13 ++++++++-----
> >>   1 file changed, 8 insertions(+), 5 deletions(-)
> >>
> >> diff --git a/drivers/gpu/drm/kmb/kmb_plane.c
> >> b/drivers/gpu/drm/kmb/kmb_plane.c
> >> index 2735b8eb3537..d2bc998b65ce 100644
> >> --- a/drivers/gpu/drm/kmb/kmb_plane.c
> >> +++ b/drivers/gpu/drm/kmb/kmb_plane.c
> >> @@ -342,10 +342,7 @@ static void kmb_plane_set_alpha(struct
> >> kmb_drm_private *kmb,
> >>   static void kmb_plane_atomic_update(struct drm_plane *plane,
> >>                       struct drm_atomic_state *state)
> >>   {
> >> -    struct drm_plane_state *old_plane_state =
> >> drm_atomic_get_old_plane_state(state,
> >> -                                         plane);
> >> -    struct drm_plane_state *new_plane_state =
> >> drm_atomic_get_new_plane_state(state,
> >> -                                         plane);
> >> +    struct drm_plane_state *old_plane_state, *new_plane_state;
> >>       struct drm_framebuffer *fb;
> >>       struct kmb_drm_private *kmb;
> >>       unsigned int width;
> >> @@ -360,7 +357,13 @@ static void kmb_plane_atomic_update(struct
> >> drm_plane *plane,
> >>       static dma_addr_t addr[MAX_SUB_PLANES];
> >>       struct disp_cfg *init_disp_cfg;
> >> -    if (!plane || !new_plane_state || !old_plane_state)
> >> +    if (!plane)
> >> +        return;
> >> +
> >> +    old_plane_state = drm_atomic_get_old_plane_state(state, plane);
> >> +    new_plane_state = drm_atomic_get_new_plane_state(state, plane);
> >> +
> >> +    if (!new_plane_state || !old_plane_state)
> >>           return;
> >>       fb = new_plane_state->fb;
> >
> 
> --
> Thomas Zimmermann
> Graphics Driver Developer
> SUSE Software Solutions Germany GmbH
> Maxfeldstr. 5, 90409 Nürnberg, Germany
> (HRB 36809, AG Nürnberg)
> Geschäftsführer: Ivo Totev

Re: [PATCH] drm/kmb: fix dereference before NULL check in kmb_plane_atomic_update()

[Thomas Zimmermann]

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Hi

Am 29.07.22 um 18:40 schrieb Chrisanthus, Anitha:
> Agree with Thomas, drm_atomic_commit() will not call kmb_atomic_update() with a NULL plane. This is not an actual bug.

Indeed, it's the atomic_update function. I didn't notice at first.

> 
> Thanks,
> Anitha
> 
>> -----Original Message-----
>> From: Thomas Zimmermann <tzimmermann@suse.de>
>> Sent: Friday, July 29, 2022 7:26 AM
>> To: Zeng Jingxiang <zengjx95@gmail.com>; Chrisanthus, Anitha
>> <anitha.chrisanthus@intel.com>; edmund.j.dea@intel.com; airlied@linux.ie;
>> daniel@ffwll.ch; laurent.pinchart@ideasonboard.com; maxime@cerno.tech;
>> ville.syrjala@linux.intel.com
>> Cc: Zeng Jingxiang <linuszeng@tencent.com>; linux-kernel@vger.kernel.org;
>> dri-devel@lists.freedesktop.org
>> Subject: Re: [PATCH] drm/kmb: fix dereference before NULL check in
>> kmb_plane_atomic_update()
>>
>> Hi
>>
>> Am 29.07.22 um 16:23 schrieb Thomas Zimmermann:
>>> Hi
>>>
>>> Am 29.07.22 um 05:07 schrieb Zeng Jingxiang:
>>>> From: Zeng Jingxiang <linuszeng@tencent.com>
>>>>
>>>> The "plane" pointer was access before checking if it was NULL.
>>>>
>>>> The drm_atomic_get_old_plane_state() function will dereference
>>>> the pointer "plane".
>>>> 345    struct drm_plane_state *old_plane_state =
>>>>          drm_atomic_get_old_plane_state(state, plane);
>>>> 346    struct drm_plane_state *new_plane_state =
>>>>          drm_atomic_get_new_plane_state(state, plane);
>>>>
>>>> A NULL check for "plane" indicates that it may be NULL
>>>> 363    if (!plane || !new_plane_state || !old_plane_state)
>>>
>>> Is this an actual bug that happens?
>>>
>>> All planes should always have a state. Therefore the tests for
>>> !new_plane_state and !old_plane_state can be removed, I'd say.
>>
>> Just to clarify: moving the test for !plane before using one of the
>> get_plane_state functions is a correct bugfix.
>>
>> Best regards
>> Thomas
>>
>>>
>>> Best regards
>>> Thomas
>>>
>>>>
>>>> Fixes: 977697e20b3d ("drm/atomic: Pass the full state to planes atomic
>>>> disable and update")
>>>> Fixes: 37418bf14c13 ("drm: Use state helper instead of the plane state
>>>> pointer")
>>>> Signed-off-by: Zeng Jingxiang <linuszeng@tencent.com>
>>>> ---
>>>>    drivers/gpu/drm/kmb/kmb_plane.c | 13 ++++++++-----
>>>>    1 file changed, 8 insertions(+), 5 deletions(-)
>>>>
>>>> diff --git a/drivers/gpu/drm/kmb/kmb_plane.c
>>>> b/drivers/gpu/drm/kmb/kmb_plane.c
>>>> index 2735b8eb3537..d2bc998b65ce 100644
>>>> --- a/drivers/gpu/drm/kmb/kmb_plane.c
>>>> +++ b/drivers/gpu/drm/kmb/kmb_plane.c
>>>> @@ -342,10 +342,7 @@ static void kmb_plane_set_alpha(struct
>>>> kmb_drm_private *kmb,
>>>>    static void kmb_plane_atomic_update(struct drm_plane *plane,
>>>>                        struct drm_atomic_state *state)
>>>>    {
>>>> -    struct drm_plane_state *old_plane_state =
>>>> drm_atomic_get_old_plane_state(state,
>>>> -                                         plane);
>>>> -    struct drm_plane_state *new_plane_state =
>>>> drm_atomic_get_new_plane_state(state,
>>>> -                                         plane);
>>>> +    struct drm_plane_state *old_plane_state, *new_plane_state;
>>>>        struct drm_framebuffer *fb;
>>>>        struct kmb_drm_private *kmb;
>>>>        unsigned int width;
>>>> @@ -360,7 +357,13 @@ static void kmb_plane_atomic_update(struct
>>>> drm_plane *plane,
>>>>        static dma_addr_t addr[MAX_SUB_PLANES];
>>>>        struct disp_cfg *init_disp_cfg;
>>>> -    if (!plane || !new_plane_state || !old_plane_state)
>>>> +    if (!plane)
>>>> +        return;
>>>> +
>>>> +    old_plane_state = drm_atomic_get_old_plane_state(state, plane);
>>>> +    new_plane_state = drm_atomic_get_new_plane_state(state, plane);
>>>> +
>>>> +    if (!new_plane_state || !old_plane_state)

To add to my previous reply, none of these variables can legally be NULL 
here. If plane if NULL, DRM helpers would run atomic_disable instead.

If you want to fix anything, just remove the tests entirely and save a 
few CPU cycles.

Best regards
Thomas

>>>>            return;
>>>>        fb = new_plane_state->fb;
>>>
>>
>> --
>> Thomas Zimmermann
>> Graphics Driver Developer
>> SUSE Software Solutions Germany GmbH
>> Maxfeldstr. 5, 90409 Nürnberg, Germany
>> (HRB 36809, AG Nürnberg)
>> Geschäftsführer: Ivo Totev

-- 
Thomas Zimmermann
Graphics Driver Developer
SUSE Software Solutions Germany GmbH
Maxfeldstr. 5, 90409 Nürnberg, Germany
(HRB 36809, AG Nürnberg)
Geschäftsführer: Ivo Totev

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