Fixed a silly use-after-free error in PendingResults

Testing self_heap_ptr for null, and setting it to null after deleting
it, won't work if self_heap_ptr is actually the last valid shared_ptr to
the PendingResults - then delete self_heap_ptr will delete the very
PendingResults that stores self_heap_ptr, and it will be illegal to set
self_heap_ptr to null! The call to delete self_heap_ptr must be the last
statement in the method, since the object it's in might get deleted at
that point. We can still prevent an accidental double-free by just using
a boolean that gets changed before deleting the pointer.

include/derecho/core/detail/rpc_utils.hpp

@@ -709,6 +709,13 @@ class PendingResults : public AbstractPendingResults, public std::enable_shared_
      */
     std::promise<void> signature_verified_promise;
 
+    /**
+     * A flag set to true the first time delete_self_ptr() is called, to
+     * prevent it from attempting to delete the pointer again if it is
+     * mistakenly called twice on the same object.
+     */
+    bool heap_pointer_deleted;
+
     /**
      * A raw pointer to a heap-allocated shared_ptr to this PendingResults object,
      * which is used by RemoteInvoker to locate this object when a reply arrives.
@@ -721,6 +728,7 @@ class PendingResults : public AbstractPendingResults, public std::enable_shared_
 public:
     PendingResults()
             : reply_promises_are_ready(promise_for_reply_promises.get_future()),
+              heap_pointer_deleted(false),
               self_heap_ptr(nullptr) {}
     virtual ~PendingResults() {}
 
@@ -773,10 +781,11 @@ class PendingResults : public AbstractPendingResults, public std::enable_shared_
      * method more than once, and it will have no effect after the first call.
      */
     void delete_self_ptr() {
-        if(self_heap_ptr) {
+        if(!heap_pointer_deleted) {
             dbg_default_trace("delete_self_ptr() deleting the shared_ptr at {}", fmt::ptr(self_heap_ptr));
+            heap_pointer_deleted = true;
+            //This must be the last statement in the method, since it might result in this object getting deleted
             delete self_heap_ptr;
-            self_heap_ptr = nullptr;
         }
     }
 

src/core/git_version.cpp

@@ -13,8 +13,8 @@ namespace derecho {
 const int MAJOR_VERSION = 2;
 const int MINOR_VERSION = 2;
 const int PATCH_VERSION = 0;
-const int COMMITS_AHEAD_OF_VERSION = 22;
+const int COMMITS_AHEAD_OF_VERSION = 23;
 const char* VERSION_STRING = "2.2.0";
-const char* VERSION_STRING_PLUS_COMMITS = "2.2.0+22";
+const char* VERSION_STRING_PLUS_COMMITS = "2.2.0+23";
 
 }