From 48ca8adc6dd020ba503294ca245d32fc6ecdb6e7 Mon Sep 17 00:00:00 2001
From: "Enrico Weigelt, metux IT consult" <info@metux.net>
Date: Wed, 23 Apr 2025 19:59:06 +0200
Subject: [PATCH] dix: make DeleteCallbackList() non-static and document it

Allow using it by other places outside this file, so we can also support
callback lists in dynamically allocated structures:

Those cases need to explicitly call DeleteCallbackList() before free()ing
the structures - otherwise we're getting heap corruptions, because the
actual deletion can happen asynchronously.

Signed-off-by: Enrico Weigelt, metux IT consult <info@metux.net>
---
 dix/callback_priv.h | 11 +++++++++++
 dix/dixutils.c      | 20 ++++++--------------
 2 files changed, 17 insertions(+), 14 deletions(-)

diff --git a/dix/callback_priv.h b/dix/callback_priv.h
index 828b74cf2..9f1022ef6 100644
--- a/dix/callback_priv.h
+++ b/dix/callback_priv.h
@@ -10,4 +10,15 @@
 void InitCallbackManager(void);
 void DeleteCallbackManager(void);
 
+/*
+ * @brief delete a callback list
+ *
+ * Calling this is necessary if a CallbackListPtr is used inside a dynamically
+ * allocated structure, before it is freed. If it's not done, memory corruption
+ * or segfault can happen at a much later point (eg. next server incarnation)
+ *
+ * @param pcbl pointer to the list head (CallbackListPtr)
+ */
+void DeleteCallbackList(CallbackListPtr *pcbl);
+
 #endif /* _XSERVER_CALLBACK_PRIV_H */
diff --git a/dix/dixutils.c b/dix/dixutils.c
index 359244883..b3708cec9 100644
--- a/dix/dixutils.c
+++ b/dix/dixutils.c
@@ -693,8 +693,6 @@ _DeleteCallback(CallbackListPtr *pcbl, CallbackProcPtr callback, void *data)
     return FALSE;
 }
 
-static void DeleteCallbackList(CallbackListPtr *pcbl);
-
 void
 _CallCallbacks(CallbackListPtr *pcbl, void *call_data)
 {
@@ -745,25 +743,26 @@ _CallCallbacks(CallbackListPtr *pcbl, void *call_data)
     }
 }
 
-static void
-_DeleteCallbackList(CallbackListPtr *pcbl)
+void DeleteCallbackList(CallbackListPtr *pcbl)
 {
+    if (!pcbl || !*pcbl)
+        return;
+
     CallbackListPtr cbl = *pcbl;
-    CallbackPtr cbr, nextcbr;
-    int i;
 
     if (cbl->inCallback) {
         cbl->deleted = TRUE;
         return;
     }
 
-    for (i = 0; i < numCallbackListsToCleanup; i++) {
+    for (int i = 0; i < numCallbackListsToCleanup; i++) {
         if (listsToCleanup[i] == pcbl) {
             listsToCleanup[i] = NULL;
             break;
         }
     }
 
+    CallbackPtr cbr, nextcbr;
     for (cbr = cbl->list; cbr != NULL; cbr = nextcbr) {
         nextcbr = cbr->next;
         free(cbr);
@@ -827,13 +826,6 @@ DeleteCallback(CallbackListPtr *pcbl, CallbackProcPtr callback, void *data)
     return _DeleteCallback(pcbl, callback, data);
 }
 
-static void DeleteCallbackList(CallbackListPtr *pcbl)
-{
-    if (!pcbl || !*pcbl)
-        return;
-    _DeleteCallbackList(pcbl);
-}
-
 void
 DeleteCallbackManager(void)
 {