From 74a3b2b7284ae6502dad6128cb1c3584af864cad Mon Sep 17 00:00:00 2001
From: "Enrico Weigelt, metux IT consult" <info@metux.net>
Date: Tue, 13 May 2025 16:16:18 +0200
Subject: [PATCH] randr: skip payload assembly in rrGetScreenResources() no
 data to send

If there's no data to send, the whole reply payload can be skipped entirely.
This can also ease the whole code flow, and we don't need to rely on the
individual copy loops never trying to dereference a NULL pointer.
(what the analyzer can't proof). Also scoping several some variables that
are only used when there actually is data to send.

Signed-off-by: Enrico Weigelt, metux IT consult <info@metux.net>
---
 randr/rrscreen.c | 32 ++++++++++++++------------------
 1 file changed, 14 insertions(+), 18 deletions(-)

diff --git a/randr/rrscreen.c b/randr/rrscreen.c
index b81edcc22..7ca21d410 100644
--- a/randr/rrscreen.c
+++ b/randr/rrscreen.c
@@ -489,10 +489,6 @@ rrGetScreenResources(ClientPtr client, Bool query)
     CARD8 *extra = NULL;
     unsigned long extraLen = 0;
     int i, rc, has_primary = 0;
-    RRCrtc *crtcs;
-    RROutput *outputs;
-    xRRModeInfo *modeinfos;
-    CARD8 *names;
 
     REQUEST_SIZE_MATCH(xRRGetScreenResourcesReq);
     rc = dixLookupWindow(&pWin, stuff->window, client, DixGetAttrAccess);
@@ -544,20 +540,19 @@ rrGetScreenResources(ClientPtr client, Bool query)
                       bytes_to_int32(rep.nbytesNames));
 
         extraLen = rep.length << 2;
-        if (extraLen) {
-            extra = calloc(1, extraLen);
-            if (!extra) {
-                free(modes);
-                return BadAlloc;
-            }
-        }
-        else
-            extra = NULL;
+        if (!extraLen)
+            goto finish;
 
-        crtcs = (RRCrtc *) extra;
-        outputs = (RROutput *) (crtcs + pScrPriv->numCrtcs);
-        modeinfos = (xRRModeInfo *) (outputs + pScrPriv->numOutputs);
-        names = (CARD8 *) (modeinfos + num_modes);
+        extra = calloc(1, extraLen);
+        if (!extra) {
+            free(modes);
+            return BadAlloc;
+        }
+
+        RRCrtc *crtcs = (RRCrtc *) extra;
+        RROutput *outputs = (RROutput *) (crtcs + pScrPriv->numCrtcs);
+        xRRModeInfo *modeinfos = (xRRModeInfo *) (outputs + pScrPriv->numOutputs);
+        CARD8* names = (CARD8 *) (modeinfos + num_modes);
 
         if (pScrPriv->primaryOutput && pScrPriv->primaryOutput->crtc) {
             has_primary = 1;
@@ -605,8 +600,9 @@ rrGetScreenResources(ClientPtr client, Bool query)
             memcpy(names, mode->name, mode->mode.nameLength);
             names += mode->mode.nameLength;
         }
-        free(modes);
         assert(bytes_to_int32((char *) names - (char *) extra) == rep.length);
+finish:
+        free(modes);
     }
 
     if (client->swapped) {