[PATCH 2/2] drm/amd/display: validate plane degamma LUT size for private color prop

Unlike the CRTC degamma path, which is guarded by
amdgpu_dm_verify_lut_sizes(), the per-plane degamma LUT size was never
validated before use. __set_dm_plane_degamma() passed the user-supplied
size straight into __is_lut_linear() and, for a non-linear LUT, into
__set_input_tf() -> __drm_lut_to_dc_gamma(), the latter always iterating
MAX_COLOR_LUT_ENTRIES entries regardless of the actual LUT size.

A malformed AMD_PLANE_DEGAMMA_LUT blob (e.g. a single entry) could thus
trigger a divide-by-zero in __is_lut_linear() or an out-of-bounds read in
__drm_lut_to_dc_gamma(). Reject any plane degamma LUT whose size does not
match MAX_COLOR_LUT_ENTRIES, mirroring the invariant the code already
asserts a few lines below (and which the CRTC path enforces).

The AMD_PLANE_DEGAMMA_LUT property is only exposed on builds with
AMD_PRIVATE_COLOR defined.

Fixes: 980f8710075a ("drm/amd/display: add plane degamma TF and LUT support")
Cc: [email protected]
Signed-off-by: Harry Wentland <[email protected]>
---
 drivers/gpu/drm/amd/display/amdgpu_dm/amdgpu_dm_color.c | 7 +++++++
 1 file changed, 7 insertions(+)

diff --git a/drivers/gpu/drm/amd/display/amdgpu_dm/amdgpu_dm_color.c b/drivers/gpu/drm/amd/display/amdgpu_dm/amdgpu_dm_color.c
index 26e5c89375a5..d55dc06167a8 100644
--- a/drivers/gpu/drm/amd/display/amdgpu_dm/amdgpu_dm_color.c
+++ b/drivers/gpu/drm/amd/display/amdgpu_dm/amdgpu_dm_color.c
@@ -1495,6 +1495,13 @@ __set_dm_plane_degamma(struct drm_plane_state *plane_state,
 	degamma_lut = __extract_blob_lut(dm_plane_state->degamma_lut,
 					 &degamma_size);
 
+	if (degamma_lut && degamma_size != MAX_COLOR_LUT_ENTRIES) {
+		drm_dbg(plane_state->state->dev,
+			"Invalid Plane Degamma LUT size. Should be %u but got %u.\n",
+			MAX_COLOR_LUT_ENTRIES, degamma_size);
+		return -EINVAL;
+	}
+
 	has_degamma_lut = degamma_lut &&
 			  !__is_lut_linear(degamma_lut, degamma_size);
 
-- 
2.55.0