On Wed, Mar 18, 2026 at 4:12 AM Jani Nikula <[email protected]> wrote: > > On Wed, 18 Mar 2026, Gui-Dong Han <[email protected]> wrote: > > Passing NULL to debugfs_create_str() causes a NULL pointer dereference > > upon reading, and is no longer permitted. Change the default values of > > dmc_firmware_path and vbt_firmware to empty strings (""). > > > > Existing code that consumes these parameters already verifies both > > pointer validity and string length, so empty strings are handled > > correctly. Furthermore, heap allocation is not required here: these > > debugfs parameters are created with strictly read-only permissions > > (0400). As a result, the debugfs write operation is never invoked, > > meaning the static empty string will not be erroneously freed by > > kfree(). > > > > Fixes: e9913f0bd2e1 ("drm/i915/display: move dmc_firmware_path to display > > params") > > Fixes: 29292bc6cc37 ("drm/i915/display: Move vbt_firmware module parameter > > under display") > > Signed-off-by: Gui-Dong Han <[email protected]> > > --- > > drivers/gpu/drm/i915/display/intel_display_params.h | 4 ++-- > > 1 file changed, 2 insertions(+), 2 deletions(-) > > > > diff --git a/drivers/gpu/drm/i915/display/intel_display_params.h > > b/drivers/gpu/drm/i915/display/intel_display_params.h > > index b95ecf728daa..0a8cad98d480 100644 > > --- a/drivers/gpu/drm/i915/display/intel_display_params.h > > +++ b/drivers/gpu/drm/i915/display/intel_display_params.h > > @@ -23,8 +23,8 @@ struct drm_printer; > > * debugfs file > > */ > > #define INTEL_DISPLAY_PARAMS_FOR_EACH(param) \ > > - param(char *, dmc_firmware_path, NULL, 0400) \ > > - param(char *, vbt_firmware, NULL, 0400) \ > > + param(char *, dmc_firmware_path, "", 0400) \ > > + param(char *, vbt_firmware, "", 0400) \ > > Admittedly this is all very convoluted, but these NULL pointers (or > pointers to them) are never passed to debugfs_create_str().
Hi Jani, Thanks for your review. Could you elaborate on why they are never passed? Looking at intel_display_debugfs_params.c, the intel_display_debugfs_params() function iterates over INTEL_DISPLAY_PARAMS_FOR_EACH using the REGISTER macro. This eventually calls _intel_display_param_create_file(), which uses _Generic to dispatch char ** types to debugfs_create_str(). Thanks.
