On Wed, Dec 1, 2021 at 4:29 PM Zhou Qingyang zhou1615@umn.edu wrote:

In cdv_intel_dp_get_modes(), the third return value of drm_mode_duplicate() is assigned to mode and used in drm_mode_probed_add(). drm_mode_probed_add() passes mode->head to list_add_tail(). list_add_tail() will further call __list_add() and there is a dereference of mode->head in __list_add(), which could lead to a wild pointer dereference on failure of drm_mode_duplicate().

Fix this bug by adding a check of mode.

This bug was found by a static analyzer. The analysis employs differential checking to identify inconsistent security operations (e.g., checks or kfrees) between two code paths and confirms that the inconsistent operations are not recovered in the current function or the callers, so they constitute bugs.

Note that, as a bug found by static analysis, it can be a false positive or hard to trigger. Multiple researchers have cross-reviewed the bug.

Is it really necessary to explain what the static analyzer does and that it can be faulty in every single patch? "This bug was found by a static analyzer" is enough for me.

Builds with CONFIG_DRM_GMA500=m show no new warnings, and our static analyzer no longer warns about this code.

I assume all patches to be at least compile tested before submitted, so if you didn't actually run this code on hardware it's better to replace the above with: "Only compile tested".

-Patrik

Fixes: d112a8163f83 ("gma500/cdv: Add eDP support") Signed-off-by: Zhou Qingyang zhou1615@umn.edu

---

Changes in V2:

• Instead of returning -ENOMEM, this patch returns 0
• Use DRM_DEBUG_KMS to report the failure of drm_mode_duplicate()

drivers/gpu/drm/gma500/cdv_intel_dp.c | 5 +++++ 1 file changed, 5 insertions(+)

diff --git a/drivers/gpu/drm/gma500/cdv_intel_dp.c b/drivers/gpu/drm/gma500/cdv_intel_dp.c index ba6ad1466374..bf47db488b7b 100644 --- a/drivers/gpu/drm/gma500/cdv_intel_dp.c +++ b/drivers/gpu/drm/gma500/cdv_intel_dp.c @@ -1773,6 +1773,11 @@ static int cdv_intel_dp_get_modes(struct drm_connector *connector) if (intel_dp->panel_fixed_mode != NULL) { struct drm_display_mode *mode; mode = drm_mode_duplicate(dev, intel_dp->panel_fixed_mode);

•                   if (!mode) {
  

•                           DRM_DEBUG_KMS("Failure in drm_mode_duplicate()\n");
  

•                           return 0;
  

•                   }
  

•                   drm_mode_probed_add(connector, mode);
                    return 1;
            }
  

-- 2.25.1