drm/i915/bios: double check array-boundary in parse_sdvo_lvds_data

During static analysis, a concern was raised that we may access the
dtd->dtd[] array out of bounds, because we are not checking whether
the index we use is larger than the array.

This should not be a problem as is, because the enumeration that is
used for this index comes from "panel_type", which uses an enumeration
with 4 items.  But if this enumeration is ever changed, it can lead to
hard-to-detect bugs, so better double-check it before using it as an
index to the array.
Signed-off-by: Luca Coelho <luciano.coelho@intel.com>
Reviewed-by: Rodrigo Vivi <rodrigo.vivi@intel.com>
Signed-off-by: Suraj Kandpal <suraj.kandpal@intel.com>
Link: https://patchwork.freedesktop.org/patch/msgid/20240528112901.476068-2-luciano.coelho@intel.com

drivers/gpu/drm/i915/display/intel_bios.c

@@ -1120,6 +1120,18 @@ parse_sdvo_lvds_data(struct drm_i915_private *i915,
 	if (!dtd)
 		return;
 
+	/*
+	 * This should not happen, as long as the panel_type
+	 * enumeration doesn't grow over 4 items.  But if it does, it
+	 * could lead to hard-to-detect bugs, so better double-check
+	 * it here to be sure.
+	 */
+	if (index >= ARRAY_SIZE(dtd->dtd)) {
+		drm_err(&i915->drm, "index %d is larger than dtd->dtd[4] array\n",
+			index);
+		return;
+	}
+
 	panel_fixed_mode = kzalloc(sizeof(*panel_fixed_mode), GFP_KERNEL);
 	if (!panel_fixed_mode)
 		return;