[PATCH AUTOSEL 5.10 08/34] drm/amd/display: Add NULL pointer checks in dm_force_atomic_commit()

[Sasha Levin <sashal@kernel.org>]

From: Srinivasan Shanmugam <srinivasan.shanmugam@amd.com>

[ Upstream commit 3f397cd203f247879c2f1a061e90d4c8d23655de ]

This commit updates the dm_force_atomic_commit function to replace the
usage of PTR_ERR_OR_ZERO with IS_ERR for checking error states after
retrieving the Connector (drm_atomic_get_connector_state), CRTC
(drm_atomic_get_crtc_state), and Plane (drm_atomic_get_plane_state)
states.

The function utilized PTR_ERR_OR_ZERO for error checking. However, this
approach is inappropriate in this context because the respective
functions do not return NULL; they return pointers that encode errors.

This change ensures that error pointers are properly checked using
IS_ERR before attempting to dereference.

Cc: Harry Wentland <harry.wentland@amd.com>
Cc: Nicholas Kazlauskas <nicholas.kazlauskas@amd.com>
Cc: Tom Chung <chiahsuan.chung@amd.com>
Cc: Roman Li <roman.li@amd.com>
Cc: Alex Hung <alex.hung@amd.com>
Cc: Aurabindo Pillai <aurabindo.pillai@amd.com>
Signed-off-by: Srinivasan Shanmugam <srinivasan.shanmugam@amd.com>
Reviewed-by: Aurabindo Pillai <aurabindo.pillai@amd.com>
Signed-off-by: Alex Deucher <alexander.deucher@amd.com>
Signed-off-by: Sasha Levin <sashal@kernel.org>
---

Based on my analysis, here's my assessment: **YES** This commit should
be backported to stable kernel trees. Here's my detailed analysis: ##
Commit Analysis **1. Bug Fix Nature:** This commit fixes a clear
programming error where `PTR_ERR_OR_ZERO()` was incorrectly used to
check error pointers returned by `drm_atomic_get_connector_state()`,
`drm_atomic_get_crtc_state()`, and `drm_atomic_get_plane_state()`. The
commit message clearly states these functions "do not return NULL; they
return pointers that encode errors." **2. Specific Code Issues Fixed:**
- **Before:** Used `PTR_ERR_OR_ZERO(conn_state)` which is inappropriate
since these functions never return NULL - **After:** Uses
`IS_ERR(conn_state)` followed by `PTR_ERR(conn_state)` which is the
correct pattern for error pointer checking **3. Comparison with Similar
Commits:** Looking at the provided examples, this commit closely matches
**Similar Commit #4 (Status: YES)** which also: - Adds null pointer
checks for proper error handling - Fixes potential crashes from
dereferencing error pointers - Is a small, contained bug fix - Addresses
static analysis findings (Coverity-style issues) **4. Risk Assessment:**
- **Low Risk:** The change is minimal and only affects error handling
paths - **No Architectural Changes:** This is purely a bug fix with no
feature additions - **Contained Impact:** Only affects the
`dm_force_atomic_commit()` function in AMD display driver - **Improves
Stability:** Prevents potential kernel crashes from dereferencing error
pointers **5. Stable Tree Criteria Met:** - ✅ Fixes an important bug
(potential crash) - ✅ Small and contained change - ✅ No new features
introduced - ✅ Minimal regression risk - ✅ Clear fix for incorrect API
usage **6. Critical System Impact:** The DRM subsystem is critical for
display functionality, and improper error handling in atomic commits
could lead to: - Kernel oops/crashes during display mode changes -
System instability during hotplug events - Potential security
implications from dereferencing invalid pointers The fix ensures proper
error propagation in the display driver's atomic commit path, which is
essential for system stability.

 .../gpu/drm/amd/display/amdgpu_dm/amdgpu_dm.c  | 18 ++++++++++++------
 1 file changed, 12 insertions(+), 6 deletions(-)

diff --git a/drivers/gpu/drm/amd/display/amdgpu_dm/amdgpu_dm.c b/drivers/gpu/drm/amd/display/amdgpu_dm/amdgpu_dm.c
index 260133562db53..45420968e5f12 100644
--- a/drivers/gpu/drm/amd/display/amdgpu_dm/amdgpu_dm.c
+++ b/drivers/gpu/drm/amd/display/amdgpu_dm/amdgpu_dm.c
@@ -8098,16 +8098,20 @@ static int dm_force_atomic_commit(struct drm_connector *connector)
 	 */
 	conn_state = drm_atomic_get_connector_state(state, connector);
 
-	ret = PTR_ERR_OR_ZERO(conn_state);
-	if (ret)
+	/* Check for error in getting connector state */
+	if (IS_ERR(conn_state)) {
+		ret = PTR_ERR(conn_state);
 		goto out;
+	}
 
 	/* Attach crtc to drm_atomic_state*/
 	crtc_state = drm_atomic_get_crtc_state(state, &disconnected_acrtc->base);
 
-	ret = PTR_ERR_OR_ZERO(crtc_state);
-	if (ret)
+	/* Check for error in getting crtc state */
+	if (IS_ERR(crtc_state)) {
+		ret = PTR_ERR(crtc_state);
 		goto out;
+	}
 
 	/* force a restore */
 	crtc_state->mode_changed = true;
@@ -8115,9 +8119,11 @@ static int dm_force_atomic_commit(struct drm_connector *connector)
 	/* Attach plane to drm_atomic_state */
 	plane_state = drm_atomic_get_plane_state(state, plane);
 
-	ret = PTR_ERR_OR_ZERO(plane_state);
-	if (ret)
+	/* Check for error in getting plane state */
+	if (IS_ERR(plane_state)) {
+		ret = PTR_ERR(plane_state);
 		goto out;
+	}
 
 	/* Call commit internally with the state we just constructed */
 	ret = drm_atomic_commit(state);
-- 
2.39.5