Fix spurious appsec munmaps in ZTS mode (#3590)

Once any ZTS thread shuts down, _shared_state is munmap'ped().
It will be unmapped and any other later mapping may happen at that same place through bad luck. If another thread shuts down, it will munmap this again and accesses to the later mapping are now crashing.

Signed-off-by: Bob Weinand <[email protected]>

Author: bwoebi

CHANGELOG.md

@@ -52,6 +52,7 @@ Changelog for older versions can be found in our [release page](https://github.c
 
 ### Fixed
 - Use abstract namespace on linux #3525
+- Fix spurious munmaps in ZTS mode #3590
 
 ### Internal
 - Improvements for appsec libxml2 usage #3564

appsec/src/extension/helper_process.c

@@ -88,15 +88,17 @@ void dd_helper_startup(void)
 #endif
 }
 
-void dd_helper_shutdown(void) {}
+void dd_helper_shutdown(void)
+{
+    if (_shared_state) {
+        munmap(_shared_state, sizeof(dd_helper_shared_state));
+    }
+}
 
 void dd_helper_gshutdown(void)
 {
     pefree(_mgr.socket_path, 1);
     pefree(_mgr.lock_path, 1);
-    if (_shared_state) {
-        munmap(_shared_state, sizeof(dd_helper_shared_state));
-    }
 }
 
 void dd_helper_rshutdown(void)