[PATCH] drm/atomic-helper: Validate pointer before dereference

[PATCH] drm/atomic-helper: Validate pointer before dereference

[Rodrigo Siqueira]

The function disable_outputs() and
drm_atomic_helper_commit_modeset_enables() tries to retrieve
helper_private from the target CRTC, for dereferencing some operations.
However, the current implementation does not check whether
helper_private is null and, if not, if it has a valid pointer to a dpms
and commit functions. This commit adds pointer validations before
trying to dereference the dpms and commit function.

Signed-off-by: Rodrigo Siqueira <rodrigosiqueiramelo@gmail.com>
---
 drivers/gpu/drm/drm_atomic_helper.c | 30 ++++++++++++++++-------------
 1 file changed, 17 insertions(+), 13 deletions(-)

diff --git a/drivers/gpu/drm/drm_atomic_helper.c b/drivers/gpu/drm/drm_atomic_helper.c
index 540a77a2ade9..fbeef7c461fc 100644
--- a/drivers/gpu/drm/drm_atomic_helper.c
+++ b/drivers/gpu/drm/drm_atomic_helper.c
@@ -1028,14 +1028,16 @@ disable_outputs(struct drm_device *dev, struct drm_atomic_state *old_state)
 
 
 		/* Right function depends upon target state. */
-		if (new_crtc_state->enable && funcs->prepare)
-			funcs->prepare(crtc);
-		else if (funcs->atomic_disable)
-			funcs->atomic_disable(crtc, old_crtc_state);
-		else if (funcs->disable)
-			funcs->disable(crtc);
-		else
-			funcs->dpms(crtc, DRM_MODE_DPMS_OFF);
+		if (funcs) {
+			if (new_crtc_state->enable && funcs->prepare)
+				funcs->prepare(crtc);
+			else if (funcs->atomic_disable)
+				funcs->atomic_disable(crtc, old_crtc_state);
+			else if (funcs->disable)
+				funcs->disable(crtc);
+			else if (funcs->dpms)
+				funcs->dpms(crtc, DRM_MODE_DPMS_OFF);
+		}
 
 		if (!(dev->irq_enabled && dev->num_crtcs))
 			continue;
@@ -1277,11 +1279,13 @@ void drm_atomic_helper_commit_modeset_enables(struct drm_device *dev,
 		if (new_crtc_state->enable) {
 			DRM_DEBUG_ATOMIC("enabling [CRTC:%d:%s]\n",
 					 crtc->base.id, crtc->name);
-
-			if (funcs->atomic_enable)
-				funcs->atomic_enable(crtc, old_crtc_state);
-			else
-				funcs->commit(crtc);
+			if (funcs) {
+				if (funcs->atomic_enable)
+					funcs->atomic_enable(crtc,
+							     old_crtc_state);
+				else if (funcs->atomic_enable)
+					funcs->commit(crtc);
+			}
 		}
 	}
 
-- 
2.21.0

Re: [PATCH] drm/atomic-helper: Validate pointer before dereference

[Sam Ravnborg]

Hi Rodrigo


On Mon, Mar 11, 2019 at 06:01:20PM -0300, Rodrigo Siqueira wrote:
> The function disable_outputs() and
> drm_atomic_helper_commit_modeset_enables() tries to retrieve
> helper_private from the target CRTC, for dereferencing some operations.
> However, the current implementation does not check whether
> helper_private is null and, if not, if it has a valid pointer to a dpms
> and commit functions. This commit adds pointer validations before
> trying to dereference the dpms and commit function.
> 
> Signed-off-by: Rodrigo Siqueira <rodrigosiqueiramelo@gmail.com>
> ---
>  drivers/gpu/drm/drm_atomic_helper.c | 30 ++++++++++++++++-------------
>  1 file changed, 17 insertions(+), 13 deletions(-)
> 
> @@ -1277,11 +1279,13 @@ void drm_atomic_helper_commit_modeset_enables(struct drm_device *dev,
>  		if (new_crtc_state->enable) {
>  			DRM_DEBUG_ATOMIC("enabling [CRTC:%d:%s]\n",
>  					 crtc->base.id, crtc->name);
This DEBUG_ print is only relevant if the code actually
do something in the following.
So it seems more correct to fix the upper if () to:

>               if (new_crtc_state->enable && funcs != NULL) {
>  			DRM_DEBUG_ATOMIC("enabling [CRTC:%d:%s]\n",
			...

The you also loose one indent and the calls are nicer.

(If used "funcs != NULL", but this is a matter of taste).

	Sam

Re: [PATCH] drm/atomic-helper: Validate pointer before dereference

[Gerd Hoffmann]

  Hi,

> -			if (funcs->atomic_enable)
> -				funcs->atomic_enable(crtc, old_crtc_state);
> -			else
> -				funcs->commit(crtc);
> +			if (funcs) {
> +				if (funcs->atomic_enable)
> +					funcs->atomic_enable(crtc,
> +							     old_crtc_state);
> +				else if (funcs->atomic_enable)

"if (funcs->commit)" I guess?

> +					funcs->commit(crtc);
> +			}

cheers,
  Gerd

Re: [PATCH] drm/atomic-helper: Validate pointer before dereference

[Daniel Vetter]

On Mon, Mar 11, 2019 at 06:01:20PM -0300, Rodrigo Siqueira wrote:
> The function disable_outputs() and
> drm_atomic_helper_commit_modeset_enables() tries to retrieve
> helper_private from the target CRTC, for dereferencing some operations.
> However, the current implementation does not check whether
> helper_private is null and, if not, if it has a valid pointer to a dpms
> and commit functions. This commit adds pointer validations before
> trying to dereference the dpms and commit function.
> 
> Signed-off-by: Rodrigo Siqueira <rodrigosiqueiramelo@gmail.com>

Please also adjust the kerneldoc for these functions. And I think the
patch subject can be improved, e.g. "Make ->atomic_enable/disable crtc
callbacks optional". Describe what you're trying to achieve in the
summary, not how you achieve it.
> ---
>  drivers/gpu/drm/drm_atomic_helper.c | 30 ++++++++++++++++-------------
>  1 file changed, 17 insertions(+), 13 deletions(-)
> 
> diff --git a/drivers/gpu/drm/drm_atomic_helper.c b/drivers/gpu/drm/drm_atomic_helper.c
> index 540a77a2ade9..fbeef7c461fc 100644
> --- a/drivers/gpu/drm/drm_atomic_helper.c
> +++ b/drivers/gpu/drm/drm_atomic_helper.c
> @@ -1028,14 +1028,16 @@ disable_outputs(struct drm_device *dev, struct drm_atomic_state *old_state)
>  
>  
>  		/* Right function depends upon target state. */
> -		if (new_crtc_state->enable && funcs->prepare)
> -			funcs->prepare(crtc);
> -		else if (funcs->atomic_disable)
> -			funcs->atomic_disable(crtc, old_crtc_state);
> -		else if (funcs->disable)
> -			funcs->disable(crtc);
> -		else
> -			funcs->dpms(crtc, DRM_MODE_DPMS_OFF);
> +		if (funcs) {

I don't think making funcs optional is a good idea. If you have a crtc
with no functions implemented, it's not terribly useful.

Also making functions optional just here is not going to help if we still
require it everywhere else.
-Daniel

> +			if (new_crtc_state->enable && funcs->prepare)
> +				funcs->prepare(crtc);
> +			else if (funcs->atomic_disable)
> +				funcs->atomic_disable(crtc, old_crtc_state);
> +			else if (funcs->disable)
> +				funcs->disable(crtc);
> +			else if (funcs->dpms)
> +				funcs->dpms(crtc, DRM_MODE_DPMS_OFF);
> +		}
>  
>  		if (!(dev->irq_enabled && dev->num_crtcs))
>  			continue;
> @@ -1277,11 +1279,13 @@ void drm_atomic_helper_commit_modeset_enables(struct drm_device *dev,
>  		if (new_crtc_state->enable) {
>  			DRM_DEBUG_ATOMIC("enabling [CRTC:%d:%s]\n",
>  					 crtc->base.id, crtc->name);
> -
> -			if (funcs->atomic_enable)
> -				funcs->atomic_enable(crtc, old_crtc_state);
> -			else
> -				funcs->commit(crtc);
> +			if (funcs) {
> +				if (funcs->atomic_enable)
> +					funcs->atomic_enable(crtc,
> +							     old_crtc_state);
> +				else if (funcs->atomic_enable)
> +					funcs->commit(crtc);
> +			}
>  		}
>  	}
>  
> -- 
> 2.21.0

-- 
Daniel Vetter
Software Engineer, Intel Corporation
http://blog.ffwll.ch

Re: [PATCH] drm/atomic-helper: Validate pointer before dereference

[Rodrigo Siqueira]

Hi,

First of all, thanks for the feedback.

I will fix all the problems pointed out in the review.

I just have two inline questions.

On 03/12, Daniel Vetter wrote:
> On Mon, Mar 11, 2019 at 06:01:20PM -0300, Rodrigo Siqueira wrote:
> > The function disable_outputs() and
> > drm_atomic_helper_commit_modeset_enables() tries to retrieve
> > helper_private from the target CRTC, for dereferencing some operations.
> > However, the current implementation does not check whether
> > helper_private is null and, if not, if it has a valid pointer to a dpms
> > and commit functions. This commit adds pointer validations before
> > trying to dereference the dpms and commit function.
> > 
> > Signed-off-by: Rodrigo Siqueira <rodrigosiqueiramelo@gmail.com>
> 
> Please also adjust the kerneldoc for these functions. And I think the
> patch subject can be improved, e.g. "Make ->atomic_enable/disable crtc
> callbacks optional". Describe what you're trying to achieve in the
> summary, not how you achieve it.

Do I need to add information which says that both functions are
optional? I'm asking because the description related to the affected
functions and struct looks good for me [1,2,3].

1. Documentation for drm_crtc_helper_funcs:
https://dri.freedesktop.org/docs/drm/gpu/drm-kms-helpers.html?highlight=drm_crtc_helper_funcs#c.drm_crtc_helper_funcs

2. Documentation for drm_atomic_helper_commit_modeset_enables():
https://dri.freedesktop.org/docs/drm/gpu/drm-kms-helpers.html?highlight=drm_atomic_helper_commit_modeset_enables#c.drm_atomic_helper_commit_modeset_enables

3. Documentation for drm_atomic_helper_commit_modeset_disables():
https://dri.freedesktop.org/docs/drm/gpu/drm-kms-helpers.html?highlight=drm_atomic_helper_commit_modeset_disables#c.drm_atomic_helper_commit_modeset_disables

> > ---
> >  drivers/gpu/drm/drm_atomic_helper.c | 30 ++++++++++++++++-------------
> >  1 file changed, 17 insertions(+), 13 deletions(-)
> > 
> > diff --git a/drivers/gpu/drm/drm_atomic_helper.c b/drivers/gpu/drm/drm_atomic_helper.c
> > index 540a77a2ade9..fbeef7c461fc 100644
> > --- a/drivers/gpu/drm/drm_atomic_helper.c
> > +++ b/drivers/gpu/drm/drm_atomic_helper.c
> > @@ -1028,14 +1028,16 @@ disable_outputs(struct drm_device *dev, struct drm_atomic_state *old_state)
> >  
> >  
> >  		/* Right function depends upon target state. */
> > -		if (new_crtc_state->enable && funcs->prepare)
> > -			funcs->prepare(crtc);
> > -		else if (funcs->atomic_disable)
> > -			funcs->atomic_disable(crtc, old_crtc_state);
> > -		else if (funcs->disable)
> > -			funcs->disable(crtc);
> > -		else
> > -			funcs->dpms(crtc, DRM_MODE_DPMS_OFF);
> > +		if (funcs) {
> 
> I don't think making funcs optional is a good idea. If you have a crtc
> with no functions implemented, it's not terribly useful.
> 
> Also making functions optional just here is not going to help if we still
> require it everywhere else.

Should I remove the other occurrence of "if (funcs)" inside
disable_outputs() and drm_atomic_helper_commit_modeset_enables()? Both
functions, already had this before.

Best Regards

> -Daniel
> 
> > +			if (new_crtc_state->enable && funcs->prepare)
> > +				funcs->prepare(crtc);
> > +			else if (funcs->atomic_disable)
> > +				funcs->atomic_disable(crtc, old_crtc_state);
> > +			else if (funcs->disable)
> > +				funcs->disable(crtc);
> > +			else if (funcs->dpms)
> > +				funcs->dpms(crtc, DRM_MODE_DPMS_OFF);
> > +		}
> >  
> >  		if (!(dev->irq_enabled && dev->num_crtcs))
> >  			continue;
> > @@ -1277,11 +1279,13 @@ void drm_atomic_helper_commit_modeset_enables(struct drm_device *dev,
> >  		if (new_crtc_state->enable) {
> >  			DRM_DEBUG_ATOMIC("enabling [CRTC:%d:%s]\n",
> >  					 crtc->base.id, crtc->name);
> > -
> > -			if (funcs->atomic_enable)
> > -				funcs->atomic_enable(crtc, old_crtc_state);
> > -			else
> > -				funcs->commit(crtc);
> > +			if (funcs) {
> > +				if (funcs->atomic_enable)
> > +					funcs->atomic_enable(crtc,
> > +							     old_crtc_state);
> > +				else if (funcs->atomic_enable)
> > +					funcs->commit(crtc);
> > +			}
> >  		}
> >  	}
> >  
> > -- 
> > 2.21.0
> 
> -- 
> Daniel Vetter
> Software Engineer, Intel Corporation
> http://blog.ffwll.ch

-- 
Rodrigo Siqueira
https://siqueira.tech
Graduate Student
Department of Computer Science
University of São Paulo