2024-03-01 09:25:34

by Aleksandr Burakov

Subject: [PATCH] drm/qxl: fix NULL dereference in qxl_add_mode

Return value of a function 'drm_cvt_mode' is dereferenced without
checking for NULL but drm_mode_create() in drm_cvt_mode() may
return NULL value in case of memory allocation error.

Found by Linux Verification Center (linuxtesting.org) with SVACE.

Fixes: 1b043677d4be ("drm/qxl: add qxl_add_mode helper function")
Signed-off-by: Aleksandr Burakov <[email protected]>
---
drivers/gpu/drm/qxl/qxl_display.c | 4 +++-
1 file changed, 3 insertions(+), 1 deletion(-)

diff --git a/drivers/gpu/drm/qxl/qxl_display.c b/drivers/gpu/drm/qxl/qxl_display.c
index a152a7c6db21..447532c29e02 100644
--- a/drivers/gpu/drm/qxl/qxl_display.c
+++ b/drivers/gpu/drm/qxl/qxl_display.c
@@ -236,8 +236,10 @@ static int qxl_add_mode(struct drm_connector *connector,
return 0;

mode = drm_cvt_mode(dev, width, height, 60, false, false, false);
- if (preferred)
+ if (preferred && mode)
mode->type |= DRM_MODE_TYPE_PREFERRED;
+ else
+ return 0;
mode->hdisplay = width;
mode->vdisplay = height;
drm_mode_set_name(mode);
--
2.25.1

2024-03-01 10:54:35

by Gerd Hoffmann

Subject: Re: [PATCH] drm/qxl: fix NULL dereference in qxl_add_mode

On Fri, Mar 01, 2024 at 11:55:11AM +0300, Aleksandr Burakov wrote:
> Return value of a function 'drm_cvt_mode' is dereferenced without
> checking for NULL but drm_mode_create() in drm_cvt_mode() may
> return NULL value in case of memory allocation error.
>
> Found by Linux Verification Center (linuxtesting.org) with SVACE.
>
> Fixes: 1b043677d4be ("drm/qxl: add qxl_add_mode helper function")
> Signed-off-by: Aleksandr Burakov <[email protected]>
> ---
> drivers/gpu/drm/qxl/qxl_display.c | 4 +++-
> 1 file changed, 3 insertions(+), 1 deletion(-)
>
> diff --git a/drivers/gpu/drm/qxl/qxl_display.c b/drivers/gpu/drm/qxl/qxl_display.c
> index a152a7c6db21..447532c29e02 100644
> --- a/drivers/gpu/drm/qxl/qxl_display.c
> +++ b/drivers/gpu/drm/qxl/qxl_display.c
> @@ -236,8 +236,10 @@ static int qxl_add_mode(struct drm_connector *connector,
> return 0;
>
> mode = drm_cvt_mode(dev, width, height, 60, false, false, false);
> - if (preferred)
> + if (preferred && mode)
> mode->type |= DRM_MODE_TYPE_PREFERRED;
> + else
> + return 0;
> mode->hdisplay = width;

That doesn't fix the NULL pointer dereference in case "preferred" is
false.

I'd suggest "if (!mode) return 0" instead.

2024-03-01 12:27:06

by Aleksandr Burakov

Subject: [PATCH v2] drm/qxl: fix NULL dereference in qxl_add_mode

Return value of a function 'drm_cvt_mode' is dereferenced without
checking for NULL but drm_mode_create() in drm_cvt_mode() may
return NULL value in case of memory allocation error.

Found by Linux Verification Center (linuxtesting.org) with SVACE.

Fixes: 1b043677d4be ("drm/qxl: add qxl_add_mode helper function")
Signed-off-by: Aleksandr Burakov <[email protected]>
---
v2: case with false value of 'preferred' is now taken into account
drivers/gpu/drm/qxl/qxl_display.c | 3 +++
1 file changed, 3 insertions(+)

diff --git a/drivers/gpu/drm/qxl/qxl_display.c b/drivers/gpu/drm/qxl/qxl_display.c
index a152a7c6db21..d6dece7a0ed2 100644
--- a/drivers/gpu/drm/qxl/qxl_display.c
+++ b/drivers/gpu/drm/qxl/qxl_display.c
@@ -236,6 +236,9 @@ static int qxl_add_mode(struct drm_connector *connector,
return 0;

mode = drm_cvt_mode(dev, width, height, 60, false, false, false);
+ if (!mode)
+ return 0;
+
if (preferred)
mode->type |= DRM_MODE_TYPE_PREFERRED;
mode->hdisplay = width;
--
2.25.1