From f7280e51db4e599e043801b00ae6603e498e80bc Mon Sep 17 00:00:00 2001
From: "Enrico Weigelt, metux IT consult" <info@metux.net>
Date: Thu, 4 Jul 2024 14:48:43 +0200
Subject: [PATCH] Xext: vidmode: tidy up multi-version request control flow,
 part 1

Some requests using different structs dependending on which protocol version
(v1 vs. v2) had been selected. That's is handled by coverting v1 structs into v2,
before proceeding with the actual handling.

The code flow of this is very complex and hard to understand. Cleaning this up
in several smaller steps, that are easier to digest.

This moving the request size check into the if-version-X branches, to make it
some bit easier to undertand.

Signed-off-by: Enrico Weigelt, metux IT consult <info@metux.net>
---
 Xext/vidmode.c | 50 ++++++++++++++++++++++++++++++++------------------
 1 file changed, 32 insertions(+), 18 deletions(-)

diff --git a/Xext/vidmode.c b/Xext/vidmode.c
index 06ac3c49c..00cdc4239 100644
--- a/Xext/vidmode.c
+++ b/Xext/vidmode.c
@@ -460,12 +460,16 @@ ProcVidModeAddModeLine(ClientPtr client)
         len =
             client->req_len -
             bytes_to_int32(sizeof(xXF86OldVidModeAddModeLineReq));
+        if (len != oldstuff->privsize)
+            return BadLength;
     }
     else {
         REQUEST_AT_LEAST_SIZE(xXF86VidModeAddModeLineReq);
         len =
             client->req_len -
             bytes_to_int32(sizeof(xXF86VidModeAddModeLineReq));
+        if (len != stuff->privsize)
+            return BadLength;
     }
 
     if (ver < 2) {
@@ -515,9 +519,6 @@ ProcVidModeAddModeLine(ClientPtr client)
            stuff->after_vsyncend, stuff->after_vtotal,
            (unsigned long) stuff->after_flags);
 
-    if (len != stuff->privsize)
-        return BadLength;
-
     if (stuff->screen >= screenInfo.numScreens)
         return BadValue;
     pScreen = screenInfo.screens[stuff->screen];
@@ -634,12 +635,28 @@ ProcVidModeDeleteModeLine(ClientPtr client)
         len =
             client->req_len -
             bytes_to_int32(sizeof(xXF86OldVidModeDeleteModeLineReq));
+        if (len != oldstuff->privsize) {
+            DebugF("req_len = %ld, sizeof(Req) = %d, privsize = %ld, "
+                   "len = %d, length = %d\n",
+                   (unsigned long) client->req_len,
+                   (int) sizeof(xXF86VidModeDeleteModeLineReq) >> 2,
+                   (unsigned long) stuff->privsize, len, client->req_len);
+            return BadLength;
+        }
     }
     else {
         REQUEST_AT_LEAST_SIZE(xXF86VidModeDeleteModeLineReq);
         len =
             client->req_len -
             bytes_to_int32(sizeof(xXF86VidModeDeleteModeLineReq));
+        if (len != stuff->privsize) {
+            DebugF("req_len = %ld, sizeof(Req) = %d, privsize = %ld, "
+                   "len = %d, length = %d\n",
+                   (unsigned long) client->req_len,
+                   (int) sizeof(xXF86VidModeDeleteModeLineReq) >> 2,
+                   (unsigned long) stuff->privsize, len, client->req_len);
+            return BadLength;
+        }
     }
 
     if (ver < 2) {
@@ -669,15 +686,6 @@ ProcVidModeDeleteModeLine(ClientPtr client)
            stuff->vdisplay, stuff->vsyncstart, stuff->vsyncend, stuff->vtotal,
            (unsigned long) stuff->flags);
 
-    if (len != stuff->privsize) {
-        DebugF("req_len = %ld, sizeof(Req) = %d, privsize = %ld, "
-               "len = %d, length = %d\n",
-               (unsigned long) client->req_len,
-               (int) sizeof(xXF86VidModeDeleteModeLineReq) >> 2,
-               (unsigned long) stuff->privsize, len, client->req_len);
-        return BadLength;
-    }
-
     if (stuff->screen >= screenInfo.numScreens)
         return BadValue;
     pScreen = screenInfo.screens[stuff->screen];
@@ -762,12 +770,16 @@ ProcVidModeModModeLine(ClientPtr client)
         len =
             client->req_len -
             bytes_to_int32(sizeof(xXF86OldVidModeModModeLineReq));
+        if (len != oldstuff->privsize)
+            return BadLength;
     }
     else {
         REQUEST_AT_LEAST_SIZE(xXF86VidModeModModeLineReq);
         len =
             client->req_len -
             bytes_to_int32(sizeof(xXF86VidModeModModeLineReq));
+        if (len != stuff->privsize)
+            return BadLength;
     }
 
     if (ver < 2) {
@@ -794,9 +806,6 @@ ProcVidModeModModeLine(ClientPtr client)
            stuff->vdisplay, stuff->vsyncstart, stuff->vsyncend,
            stuff->vtotal, (unsigned long) stuff->flags);
 
-    if (len != stuff->privsize)
-        return BadLength;
-
     if (stuff->hsyncstart < stuff->hdisplay ||
         stuff->hsyncend < stuff->hsyncstart ||
         stuff->htotal < stuff->hsyncend ||
@@ -899,12 +908,16 @@ ProcVidModeValidateModeLine(ClientPtr client)
         REQUEST_AT_LEAST_SIZE(xXF86OldVidModeValidateModeLineReq);
         len = client->req_len -
             bytes_to_int32(sizeof(xXF86OldVidModeValidateModeLineReq));
+        if (len != oldstuff->privsize)
+            return BadLength;
     }
     else {
         REQUEST_AT_LEAST_SIZE(xXF86VidModeValidateModeLineReq);
         len =
             client->req_len -
             bytes_to_int32(sizeof(xXF86VidModeValidateModeLineReq));
+        if (len != stuff->privsize)
+            return BadLength;
     }
 
     if (ver < 2) {
@@ -1063,12 +1076,16 @@ ProcVidModeSwitchToMode(ClientPtr client)
         len =
             client->req_len -
             bytes_to_int32(sizeof(xXF86OldVidModeSwitchToModeReq));
+        if (len != stuff->privsize)
+            return BadLength;
     }
     else {
         REQUEST_AT_LEAST_SIZE(xXF86VidModeSwitchToModeReq);
         len =
             client->req_len -
             bytes_to_int32(sizeof(xXF86VidModeSwitchToModeReq));
+        if (len != stuff->privsize)
+            return BadLength;
     }
 
     if (ver < 2) {
@@ -1099,9 +1116,6 @@ ProcVidModeSwitchToMode(ClientPtr client)
            stuff->vdisplay, stuff->vsyncstart, stuff->vsyncend, stuff->vtotal,
            (unsigned long) stuff->flags);
 
-    if (len != stuff->privsize)
-        return BadLength;
-
     if (stuff->screen >= screenInfo.numScreens)
         return BadValue;
     pScreen = screenInfo.screens[stuff->screen];