Index: chgfctl.c
===================================================================
RCS file: /cvsroot/xsrc/external/mit/xorg-server/dist/Xi/chgfctl.c,v
retrieving revision 1.3
diff -p -u -r1.3 chgfctl.c
--- chgfctl.c	11 Aug 2016 00:04:26 -0000	1.3
+++ chgfctl.c	27 Apr 2021 18:58:14 -0000
@@ -464,8 +464,11 @@ ProcXChangeFeedbackControl(ClientPtr cli
         break;
     case StringFeedbackClass:
     {
-        xStringFeedbackCtl *f = ((xStringFeedbackCtl *) &stuff[1]);
+        xStringFeedbackCtl *f;
 
+        REQUEST_AT_LEAST_EXTRA_SIZE(xChangeFeedbackControlReq,
+                                    sizeof(xStringFeedbackCtl));
+        f = ((xStringFeedbackCtl *) &stuff[1]);
         if (client->swapped) {
             if (len < bytes_to_int32(sizeof(xStringFeedbackCtl)))
                 return BadLength;