From 0563d172b687c60513e144d3458b9eb8982eb39b Mon Sep 17 00:00:00 2001 From: Srinivasan Shanmugam Date: Fri, 21 Nov 2025 20:23:29 +0530 Subject: [PATCH] drm/amd/display: Fix dereference-before-check for dc_link MIME-Version: 1.0 Content-Type: text/plain; charset=utf8 Content-Transfer-Encoding: 8bit The function dereferences amdgpu_dm_connector->dc_link early to initialize verified_link_cap and dc, but later still checks amdgpu_dm_connector->dc_link for NULL in the analog path. This late NULL check is redundant, introduce a local dc_link pointer, use it consistently, and drop the superfluous NULL check while using dc_link->link_id.id instead. The function uses dc_link at the very beginning without checking if it is NULL. But later in the code, it suddenly checks if dc_link is NULL. This check is too late to be useful, because the code has already used dc_link earlier. So this NULL check does nothing. We simplify the code by storing amdgpu_dm_connector->dc_link in a local dc_link variable and using it throughout the function. Since dc_link is already dereferenced early, the later NULL check is unnecessary and is removed. Fixes the below: amdgpu_dm_connector_get_modes(): variable dereferenced before check 'amdgpu_dm_connector->dc_link' drivers/gpu/drm/amd/amdgpu/../display/amdgpu_dm/amdgpu_dm.c 8845 &amdgpu_dm_connector->dc_link->verified_link_cap; 8846 const struct dc *dc = amdgpu_dm_connector->dc_link->dc; ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^ Dereference ... 8856 8857 if (amdgpu_dm_connector->dc_sink && 8858 amdgpu_dm_connector->dc_link && ^^^^^^^^^^^^^^^^^^^^^^^^^^^^ Checked too late. Presumably this NULL check could be removed? ... Fixes: d46e422f65ae ("drm/amd/display: Cleanup uses of the analog flag") Reported by: Dan Carpenter Cc: Timur Kristóf Cc: Aurabindo Pillai Cc: Roman Li Cc: Harry Wentland Cc: Tom Chung Cc: Alex Hung Cc: Ivan Lipski Signed-off-by: Srinivasan Shanmugam Reviewed-by: Timur Kristóf Signed-off-by: Alex Deucher --- drivers/gpu/drm/amd/display/amdgpu_dm/amdgpu_dm.c | 9 ++++----- 1 file changed, 4 insertions(+), 5 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 020f5a4f6463..6287cc1bd4cc 100644 --- a/drivers/gpu/drm/amd/display/amdgpu_dm/amdgpu_dm.c +++ b/drivers/gpu/drm/amd/display/amdgpu_dm/amdgpu_dm.c @@ -8854,11 +8854,11 @@ static int amdgpu_dm_connector_get_modes(struct drm_connector *connector) { struct amdgpu_dm_connector *amdgpu_dm_connector = to_amdgpu_dm_connector(connector); + struct dc_link *dc_link = amdgpu_dm_connector->dc_link; struct drm_encoder *encoder; const struct drm_edid *drm_edid = amdgpu_dm_connector->drm_edid; - struct dc_link_settings *verified_link_cap = - &amdgpu_dm_connector->dc_link->verified_link_cap; - const struct dc *dc = amdgpu_dm_connector->dc_link->dc; + struct dc_link_settings *verified_link_cap = &dc_link->verified_link_cap; + const struct dc *dc = dc_link->dc; encoder = amdgpu_dm_connector_to_encoder(connector); @@ -8870,9 +8870,8 @@ static int amdgpu_dm_connector_get_modes(struct drm_connector *connector) drm_add_modes_noedid(connector, 1920, 1080); if (amdgpu_dm_connector->dc_sink && - amdgpu_dm_connector->dc_link && amdgpu_dm_connector->dc_sink->edid_caps.analog && - dc_connector_supports_analog(amdgpu_dm_connector->dc_link->link_id.id)) { + dc_connector_supports_analog(dc_link->link_id.id)) { /* Analog monitor connected by DAC load detection. * Add common modes. It will be up to the user to select one that works. */ -- 2.47.3