drm/amd/display: Guard against NULL pointer deref when get_i2c_info f…

…ails

[ Upstream commit 44a09e3 ]

[Why]
If the BIOS table is invalid or corrupt then get_i2c_info can fail
and we dereference a NULL pointer.

[How]
Check that ddc_pin is not NULL before using it and log an error if it
is because this is unexpected.

Tested-by: Daniel Wheeler <daniel.wheeler@amd.com>
Signed-off-by: Nicholas Kazlauskas <nicholas.kazlauskas@amd.com>
Reviewed-by: Eric Yang <eric.yang2@amd.com>
Acked-by: Anson Jacob <anson.jacob@amd.com>
Signed-off-by: Alex Deucher <alexander.deucher@amd.com>
Signed-off-by: Sasha Levin <sashal@kernel.org>

drivers/gpu/drm/amd/display/dc/core/dc_link.c

@@ -1454,6 +1454,11 @@ static bool dc_link_construct(struct dc_link *link,
 		goto ddc_create_fail;
 	}
 
+	if (!link->ddc->ddc_pin) {
+		DC_ERROR("Failed to get I2C info for connector!\n");
+		goto ddc_create_fail;
+	}
+
 	link->ddc_hw_inst =
 		dal_ddc_get_line(dal_ddc_service_get_ddc_pin(link->ddc));