CVE-2025-40148: drm/amd/display: Add NULL pointer checks in dc_stream cursor attribute functions

In the Linux kernel, the following vulnerability has been resolved:

drm/amd/display: Add NULL pointer checks in dcstream cursor attribute functions

The function dcstreamsetcursorattributes() currently dereferences the stream pointer and nested members stream->ctx->dc->currentstate without checking for NULL.

All callers of these functions, such as in dcn30applyidlepoweroptimizations() and amdgpudmplanehandlecursorupdate(), already perform NULL checks before calling these functions.

Fixes below: drivers/gpu/drm/amd/amdgpu/../display/dc/core/dcstream.c:336 dcstreamprogramcursorattributes() error: we previously assumed 'stream' could be null (see line 334)

drivers/gpu/drm/amd/amdgpu/../display/dc/core/dcstream.c 327 bool dcstreamprogramcursorattributes( 328 struct dcstreamstate stream, 329 const struct dccursorattributes attributes) 330 { 331 struct dc dc; 332 bool resetidleoptimizations = false; 333 334 dc = stream ? stream->ctx->dc : NULL; ^^^^^^ The old code assumed stream could be NULL.

335 --> 336 if (dcstreamsetcursorattributes(stream, attributes)) { ^^^^^^ The refactor added an unchecked dereference.

drivers/gpu/drm/amd/amdgpu/../display/dc/core/dcstream.c 313 bool dcstreamsetcursorattributes( 314 struct dcstreamstate stream, 315 const struct dccursorattributes attributes) 316 { 317 bool result = false; 318 319 if (dcstreamcheckcursorattributes(stream, stream->ctx->dc->currentstate, attributes)) { ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^ Here. This function used to check for if stream as NULL and return false at the start. Probably we should add that back.