[PATCH v2 0/2] drm/vc4: hdmi: Fix pointer dereference before check

[PATCH v2 0/2] drm/vc4: hdmi: Fix pointer dereference before check

[José Expósito]

v1 -> v2:

As suggested by Maxime, I simplified a bit vc4_hdmi_supports_scrambling()
making it receive a struct vc4_hdmi as argument instead of a struct
drm_encoder.

Also, variables are initialized close to where they are used in the
second patch.

José Expósito (2):
  drm/vc4: hdmi: Pass vc4_hdmi to vc4_hdmi_supports_scrambling()
  drm/vc4: hdmi: Fix pointer dereference before check

 drivers/gpu/drm/vc4/vc4_hdmi.c | 14 +++++++-------
 1 file changed, 7 insertions(+), 7 deletions(-)

-- 
2.25.1

[PATCH v2 1/2] drm/vc4: hdmi: Pass vc4_hdmi to vc4_hdmi_supports_scrambling()

[José Expósito]

Simplify vc4_hdmi_supports_scrambling() by changing its first parameter
from struct drm_encoder to struct vc4_hdmi.

Signed-off-by: José Expósito <jose.exposito89@gmail.com>
---
 drivers/gpu/drm/vc4/vc4_hdmi.c | 8 +++-----
 1 file changed, 3 insertions(+), 5 deletions(-)

diff --git a/drivers/gpu/drm/vc4/vc4_hdmi.c b/drivers/gpu/drm/vc4/vc4_hdmi.c
index 0d78c800ed51..a49f88e5d2b9 100644
--- a/drivers/gpu/drm/vc4/vc4_hdmi.c
+++ b/drivers/gpu/drm/vc4/vc4_hdmi.c
@@ -124,9 +124,8 @@ static unsigned long long
 vc4_hdmi_encoder_compute_mode_clock(const struct drm_display_mode *mode,
 				    unsigned int bpc, enum vc4_hdmi_output_format fmt);
 
-static bool vc4_hdmi_supports_scrambling(struct drm_encoder *encoder)
+static bool vc4_hdmi_supports_scrambling(struct vc4_hdmi *vc4_hdmi)
 {
-	struct vc4_hdmi *vc4_hdmi = encoder_to_vc4_hdmi(encoder);
 	struct drm_display_info *display = &vc4_hdmi->connector.display_info;
 
 	lockdep_assert_held(&vc4_hdmi->mutex);
@@ -321,7 +320,6 @@ static int vc4_hdmi_reset_link(struct drm_connector *connector,
 {
 	struct drm_device *drm = connector->dev;
 	struct vc4_hdmi *vc4_hdmi = connector_to_vc4_hdmi(connector);
-	struct drm_encoder *encoder = &vc4_hdmi->encoder.base;
 	struct drm_connector_state *conn_state;
 	struct drm_crtc_state *crtc_state;
 	struct drm_crtc *crtc;
@@ -349,7 +347,7 @@ static int vc4_hdmi_reset_link(struct drm_connector *connector,
 	if (!crtc_state->active)
 		return 0;
 
-	if (!vc4_hdmi_supports_scrambling(encoder))
+	if (!vc4_hdmi_supports_scrambling(vc4_hdmi))
 		return 0;
 
 	scrambling_needed = vc4_hdmi_mode_needs_scrambling(&vc4_hdmi->saved_adjusted_mode,
@@ -867,7 +865,7 @@ static void vc4_hdmi_enable_scrambling(struct drm_encoder *encoder)
 
 	lockdep_assert_held(&vc4_hdmi->mutex);
 
-	if (!vc4_hdmi_supports_scrambling(encoder))
+	if (!vc4_hdmi_supports_scrambling(vc4_hdmi))
 		return;
 
 	if (!vc4_hdmi_mode_needs_scrambling(mode,
-- 
2.25.1

[PATCH v2 2/2] drm/vc4: hdmi: Fix pointer dereference before check

[José Expósito]

Commit 6bed2ea3cb38 ("drm/vc4: hdmi: Reset link on hotplug") introduced
the vc4_hdmi_reset_link() function. This function dereferences the
"connector" pointer before checking whether it is NULL or not.

Rework variable assignment to avoid this issue.

Fixes: 6bed2ea3cb38 ("drm/vc4: hdmi: Reset link on hotplug")
Signed-off-by: José Expósito <jose.exposito89@gmail.com>
---
 drivers/gpu/drm/vc4/vc4_hdmi.c | 6 ++++--
 1 file changed, 4 insertions(+), 2 deletions(-)

diff --git a/drivers/gpu/drm/vc4/vc4_hdmi.c b/drivers/gpu/drm/vc4/vc4_hdmi.c
index a49f88e5d2b9..6b223a5fcf6f 100644
--- a/drivers/gpu/drm/vc4/vc4_hdmi.c
+++ b/drivers/gpu/drm/vc4/vc4_hdmi.c
@@ -318,8 +318,8 @@ static int reset_pipe(struct drm_crtc *crtc,
 static int vc4_hdmi_reset_link(struct drm_connector *connector,
 			       struct drm_modeset_acquire_ctx *ctx)
 {
-	struct drm_device *drm = connector->dev;
-	struct vc4_hdmi *vc4_hdmi = connector_to_vc4_hdmi(connector);
+	struct drm_device *drm;
+	struct vc4_hdmi *vc4_hdmi;
 	struct drm_connector_state *conn_state;
 	struct drm_crtc_state *crtc_state;
 	struct drm_crtc *crtc;
@@ -330,6 +330,7 @@ static int vc4_hdmi_reset_link(struct drm_connector *connector,
 	if (!connector)
 		return 0;
 
+	drm = connector->dev;
 	ret = drm_modeset_lock(&drm->mode_config.connection_mutex, ctx);
 	if (ret)
 		return ret;
@@ -347,6 +348,7 @@ static int vc4_hdmi_reset_link(struct drm_connector *connector,
 	if (!crtc_state->active)
 		return 0;
 
+	vc4_hdmi = connector_to_vc4_hdmi(connector);
 	if (!vc4_hdmi_supports_scrambling(vc4_hdmi))
 		return 0;
 
-- 
2.25.1

Re: [PATCH v2 2/2] drm/vc4: hdmi: Fix pointer dereference before check

[Nick Desaulniers]

On Thu, Nov 10, 2022 at 02:47:52PM +0100, José Expósito wrote:
> Commit 6bed2ea3cb38 ("drm/vc4: hdmi: Reset link on hotplug") introduced
> the vc4_hdmi_reset_link() function. This function dereferences the
> "connector" pointer before checking whether it is NULL or not.
> 
> Rework variable assignment to avoid this issue.
> 
> Fixes: 6bed2ea3cb38 ("drm/vc4: hdmi: Reset link on hotplug")
> Signed-off-by: José Expósito <jose.exposito89@gmail.com>
> ---
>  drivers/gpu/drm/vc4/vc4_hdmi.c | 6 ++++--
>  1 file changed, 4 insertions(+), 2 deletions(-)
> 
> diff --git a/drivers/gpu/drm/vc4/vc4_hdmi.c b/drivers/gpu/drm/vc4/vc4_hdmi.c
> index a49f88e5d2b9..6b223a5fcf6f 100644
> --- a/drivers/gpu/drm/vc4/vc4_hdmi.c
> +++ b/drivers/gpu/drm/vc4/vc4_hdmi.c
> @@ -318,8 +318,8 @@ static int reset_pipe(struct drm_crtc *crtc,
>  static int vc4_hdmi_reset_link(struct drm_connector *connector,
>  			       struct drm_modeset_acquire_ctx *ctx)
>  {
> -	struct drm_device *drm = connector->dev;
> -	struct vc4_hdmi *vc4_hdmi = connector_to_vc4_hdmi(connector);
> +	struct drm_device *drm;
> +	struct vc4_hdmi *vc4_hdmi;

Hi, I think this change, or another in this area recently, is causing
the following warning. PTAL

drivers/gpu/drm/vc4/vc4_hdmi.c:351:14: warning: variable 'vc4_hdmi' is uninitialized when used here [-Wuninitialized]
        mutex_lock(&vc4_hdmi->mutex);
                    ^~~~~~~~
drivers/gpu/drm/vc4/vc4_hdmi.c:322:27: note: initialize the variable 'vc4_hdmi' to silence this warning
        struct vc4_hdmi *vc4_hdmi;
                                 ^
                                  = NULL

>  	struct drm_connector_state *conn_state;
>  	struct drm_crtc_state *crtc_state;
>  	struct drm_crtc *crtc;
> @@ -330,6 +330,7 @@ static int vc4_hdmi_reset_link(struct drm_connector *connector,
>  	if (!connector)
>  		return 0;
>  
> +	drm = connector->dev;
>  	ret = drm_modeset_lock(&drm->mode_config.connection_mutex, ctx);
>  	if (ret)
>  		return ret;
> @@ -347,6 +348,7 @@ static int vc4_hdmi_reset_link(struct drm_connector *connector,
>  	if (!crtc_state->active)
>  		return 0;
>  
> +	vc4_hdmi = connector_to_vc4_hdmi(connector);
>  	if (!vc4_hdmi_supports_scrambling(vc4_hdmi))
>  		return 0;
>  
> -- 
> 2.25.1
> 
> 

Re: [PATCH v2 2/2] drm/vc4: hdmi: Fix pointer dereference before check

[Nathan Chancellor]

On Thu, Nov 17, 2022 at 09:28:49AM -0800, Nick Desaulniers wrote:
> On Thu, Nov 10, 2022 at 02:47:52PM +0100, José Expósito wrote:
> > Commit 6bed2ea3cb38 ("drm/vc4: hdmi: Reset link on hotplug") introduced
> > the vc4_hdmi_reset_link() function. This function dereferences the
> > "connector" pointer before checking whether it is NULL or not.
> > 
> > Rework variable assignment to avoid this issue.
> > 
> > Fixes: 6bed2ea3cb38 ("drm/vc4: hdmi: Reset link on hotplug")
> > Signed-off-by: José Expósito <jose.exposito89@gmail.com>
> > ---
> >  drivers/gpu/drm/vc4/vc4_hdmi.c | 6 ++++--
> >  1 file changed, 4 insertions(+), 2 deletions(-)
> > 
> > diff --git a/drivers/gpu/drm/vc4/vc4_hdmi.c b/drivers/gpu/drm/vc4/vc4_hdmi.c
> > index a49f88e5d2b9..6b223a5fcf6f 100644
> > --- a/drivers/gpu/drm/vc4/vc4_hdmi.c
> > +++ b/drivers/gpu/drm/vc4/vc4_hdmi.c
> > @@ -318,8 +318,8 @@ static int reset_pipe(struct drm_crtc *crtc,
> >  static int vc4_hdmi_reset_link(struct drm_connector *connector,
> >  			       struct drm_modeset_acquire_ctx *ctx)
> >  {
> > -	struct drm_device *drm = connector->dev;
> > -	struct vc4_hdmi *vc4_hdmi = connector_to_vc4_hdmi(connector);
> > +	struct drm_device *drm;
> > +	struct vc4_hdmi *vc4_hdmi;
> 
> Hi, I think this change, or another in this area recently, is causing
> the following warning. PTAL
> 
> drivers/gpu/drm/vc4/vc4_hdmi.c:351:14: warning: variable 'vc4_hdmi' is uninitialized when used here [-Wuninitialized]
>         mutex_lock(&vc4_hdmi->mutex);
>                     ^~~~~~~~
> drivers/gpu/drm/vc4/vc4_hdmi.c:322:27: note: initialize the variable 'vc4_hdmi' to silence this warning
>         struct vc4_hdmi *vc4_hdmi;
>                                  ^
>                                   = NULL

Guess we just crossed paths but this is just a problem with -next due to
a bad conflict resolution on Stephen's part:

https://lore.kernel.org/Y3ZvffZiR+SgtY6h@dev-arch.thelio-3990X/

> >  	struct drm_connector_state *conn_state;
> >  	struct drm_crtc_state *crtc_state;
> >  	struct drm_crtc *crtc;
> > @@ -330,6 +330,7 @@ static int vc4_hdmi_reset_link(struct drm_connector *connector,
> >  	if (!connector)
> >  		return 0;
> >  
> > +	drm = connector->dev;
> >  	ret = drm_modeset_lock(&drm->mode_config.connection_mutex, ctx);
> >  	if (ret)
> >  		return ret;
> > @@ -347,6 +348,7 @@ static int vc4_hdmi_reset_link(struct drm_connector *connector,
> >  	if (!crtc_state->active)
> >  		return 0;
> >  
> > +	vc4_hdmi = connector_to_vc4_hdmi(connector);

This version of the patch is fine, as there is no mutex_lock() call
here.

> >  	if (!vc4_hdmi_supports_scrambling(vc4_hdmi))
> >  		return 0;
> >  
> > -- 
> > 2.25.1
> > 
> > 
> 

Cheers,
Nathan