Nouveau - Jun 2024 - [PATCH] drm/nouveau/dispnv04: fix null pointer dereference in nv17_tv_get_hd_modes

In nv17_tv_get_hd_modes(), the return value of drm_mode_duplicate() is
assigned to mode, which will lead to a possible NULL pointer dereference
on failure of drm_mode_duplicate(). The same applies to drm_cvt_mode().
Add a check to avoid null pointer dereference.

Cc: stable at vger.kernel.org
Signed-off-by: Ma Ke <make24 at iscas.ac.cn>
---
 drivers/gpu/drm/nouveau/dispnv04/tvnv17.c | 4 ++++
 1 file changed, 4 insertions(+)

diff --git a/drivers/gpu/drm/nouveau/dispnv04/tvnv17.c
b/drivers/gpu/drm/nouveau/dispnv04/tvnv17.c
index 670c9739e5e1..9c3dc9a5bb46 100644
--- a/drivers/gpu/drm/nouveau/dispnv04/tvnv17.c
+++ b/drivers/gpu/drm/nouveau/dispnv04/tvnv17.c
@@ -258,6 +258,8 @@ static int nv17_tv_get_hd_modes(struct drm_encoder *encoder,
 		if (modes[i].hdisplay == output_mode->hdisplay &&
 		    modes[i].vdisplay == output_mode->vdisplay) {
 			mode = drm_mode_duplicate(encoder->dev, output_mode);
+			if (!mode)
+				continue;
 			mode->type |= DRM_MODE_TYPE_PREFERRED;
 
 		} else {
@@ -265,6 +267,8 @@ static int nv17_tv_get_hd_modes(struct drm_encoder *encoder,
 					    modes[i].vdisplay, 60, false,
 					    (output_mode->flags &
 					     DRM_MODE_FLAG_INTERLACE), false);
+			if (!mode)
+				continue;
 		}
 
 		/* CVT modes are sometimes unsuitable... */
-- 
2.25.1

> In nv17_tv_get_hd_modes(), the return value of drm_mode_duplicate() is
> assigned to mode, which will lead to a possible NULL pointer dereference
> on failure of drm_mode_duplicate(). The same applies to drm_cvt_mode().
> Add a check to avoid null pointer dereference.
Can a wording approach (like the following) be a better change description?

  A null pointer is stored in the local variable ?mode? after a call
  of the function ?drm_cvt_mode? or ?drm_mode_duplicate? failed.
  This pointer was used in subsequent statements where an undesirable
  dereference will be performed then.
  Thus add corresponding return value checks.

> Cc: stable at vger.kernel.org
Would you like to add the tag ?Fixes? accordingly?


How do you think about to use a summary phrase like
?Prevent null pointer dereferences in nv17_tv_get_hd_modes()??

Regards,
Markus

Reviewed-by: Lyude Paul <lyude at redhat.com>

I will push this and the other patch that you sent upstream in just a
moment, thanks!

On Tue, 2024-06-25 at 16:10 +0800, Ma Ke wrote:
> In nv17_tv_get_hd_modes(), the return value of drm_mode_duplicate()
> is
> assigned to mode, which will lead to a possible NULL pointer
> dereference
> on failure of drm_mode_duplicate(). The same applies to
> drm_cvt_mode().
> Add a check to avoid null pointer dereference.
> 
> Cc: stable at vger.kernel.org
> Signed-off-by: Ma Ke <make24 at iscas.ac.cn>
> ---
> ?drivers/gpu/drm/nouveau/dispnv04/tvnv17.c | 4 ++++
> ?1 file changed, 4 insertions(+)
> 
> diff --git a/drivers/gpu/drm/nouveau/dispnv04/tvnv17.c
> b/drivers/gpu/drm/nouveau/dispnv04/tvnv17.c
> index 670c9739e5e1..9c3dc9a5bb46 100644
> --- a/drivers/gpu/drm/nouveau/dispnv04/tvnv17.c
> +++ b/drivers/gpu/drm/nouveau/dispnv04/tvnv17.c
> @@ -258,6 +258,8 @@ static int nv17_tv_get_hd_modes(struct
> drm_encoder *encoder,
> ?		if (modes[i].hdisplay == output_mode->hdisplay &&
> ?		??? modes[i].vdisplay == output_mode->vdisplay) {
> ?			mode = drm_mode_duplicate(encoder->dev,
> output_mode);
> +			if (!mode)
> +				continue;
> ?			mode->type |= DRM_MODE_TYPE_PREFERRED;
> ?
> ?		} else {
> @@ -265,6 +267,8 @@ static int nv17_tv_get_hd_modes(struct
> drm_encoder *encoder,
> ?					??? modes[i].vdisplay, 60,
> false,
> ?					??? (output_mode->flags &
> ?					????
> DRM_MODE_FLAG_INTERLACE), false);
> +			if (!mode)
> +				continue;
> ?		}
> ?
> ?		/* CVT modes are sometimes unsuitable... */
-- 
Cheers,
 Lyude Paul (she/her)
 Software Engineer at Red Hat