Fix T100286: Crash accessing freed depsgraph object instances

Invalidate depsgraph.object_instances when freed, this resolves a crash
when accessing the object instances after iteration has finished.

Unlike most other collections, object_instances is only valid while the
iterator is in-memory.

The Python/RNA API needs to inline int/string collection lookups so the
Python instance can be created before the iterator ends.

Reviewed By: mont29, sergey

Ref D15755

4 files changed, 176 insertions, 43 deletions

diff --git a/source/blender/makesrna/RNA_access.h b/source/blender/makesrna/RNA_access.h
index de9fa60aa5d..ddc010f27a1 100644
--- a/source/blender/makesrna/RNA_access.h
+++ b/source/blender/makesrna/RNA_access.h
@@ -430,6 +430,10 @@ int RNA_property_collection_lookup_string(PointerRNA *ptr,
                                           PointerRNA *r_ptr);
 int RNA_property_collection_lookup_string_index(
     PointerRNA *ptr, PropertyRNA *prop, const char *key, PointerRNA *r_ptr, int *r_index);
+
+bool RNA_property_collection_lookup_int_has_fn(PropertyRNA *prop);
+bool RNA_property_collection_lookup_string_has_fn(PropertyRNA *prop);
+
 /**
  * Zero return is an assignment error.
  */
diff --git a/source/blender/makesrna/intern/rna_access.c b/source/blender/makesrna/intern/rna_access.c
index 04707c01d6b..56cbcb2a7f2 100644
--- a/source/blender/makesrna/intern/rna_access.c
+++ b/source/blender/makesrna/intern/rna_access.c
@@ -4080,6 +4080,20 @@ int RNA_property_collection_lookup_index(PointerRNA *ptr,
   return -1;
 }
 
+bool RNA_property_collection_lookup_int_has_fn(PropertyRNA *prop)
+{
+  BLI_assert(RNA_property_type(prop) == PROP_COLLECTION);
+  CollectionPropertyRNA *cprop = (CollectionPropertyRNA *)rna_ensure_property(prop);
+  return cprop->lookupint != NULL;
+}
+
+bool RNA_property_collection_lookup_string_has_fn(PropertyRNA *prop)
+{
+  BLI_assert(RNA_property_type(prop) == PROP_COLLECTION);
+  CollectionPropertyRNA *cprop = (CollectionPropertyRNA *)rna_ensure_property(prop);
+  return cprop->lookupstring != NULL;
+}
+
 int RNA_property_collection_lookup_int(PointerRNA *ptr,
                                        PropertyRNA *prop,
                                        int key,
diff --git a/source/blender/makesrna/intern/rna_depsgraph.c b/source/blender/makesrna/intern/rna_depsgraph.c
index 6196f8d1ca0..f0d26362cad 100644
--- a/source/blender/makesrna/intern/rna_depsgraph.c
+++ b/source/blender/makesrna/intern/rna_depsgraph.c
@@ -43,23 +43,41 @@
 
 /* **************** Object Instance **************** */
 
+typedef struct RNA_DepsgraphIterator {
+  BLI_Iterator iter;
+#  ifdef WITH_PYTHON
+  /**
+   * Store the Python instance so the #BPy_StructRNA can be set as invalid iteration is completed.
+   * Otherwise accessing from Python (console auto-complete for e.g.) crashes, see: T100286. */
+  void *py_instance;
+#  endif
+} RNA_DepsgraphIterator;
+
+#  ifdef WITH_PYTHON
+void **rna_DepsgraphIterator_instance(PointerRNA *ptr)
+{
+  RNA_DepsgraphIterator *di = ptr->data;
+  return &di->py_instance;
+}
+#  endif
+
 static PointerRNA rna_DepsgraphObjectInstance_object_get(PointerRNA *ptr)
 {
-  BLI_Iterator *iterator = ptr->data;
-  return rna_pointer_inherit_refine(ptr, &RNA_Object, iterator->current);
+  RNA_DepsgraphIterator *di = ptr->data;
+  return rna_pointer_inherit_refine(ptr, &RNA_Object, di->iter.current);
 }
 
 static int rna_DepsgraphObjectInstance_is_instance_get(PointerRNA *ptr)
 {
-  BLI_Iterator *iterator = ptr->data;
-  DEGObjectIterData *deg_iter = (DEGObjectIterData *)iterator->data;
+  RNA_DepsgraphIterator *di = ptr->data;
+  DEGObjectIterData *deg_iter = (DEGObjectIterData *)di->iter.data;
   return (deg_iter->dupli_object_current != NULL);
 }
 
 static PointerRNA rna_DepsgraphObjectInstance_instance_object_get(PointerRNA *ptr)
 {
-  BLI_Iterator *iterator = ptr->data;
-  DEGObjectIterData *deg_iter = (DEGObjectIterData *)iterator->data;
+  RNA_DepsgraphIterator *di = ptr->data;
+  DEGObjectIterData *deg_iter = (DEGObjectIterData *)di->iter.data;
   Object *instance_object = NULL;
   if (deg_iter->dupli_object_current != NULL) {
     instance_object = deg_iter->dupli_object_current->ob;
@@ -69,24 +87,24 @@ static PointerRNA rna_DepsgraphObjectInstance_instance_object_get(PointerRNA *pt
 
 static bool rna_DepsgraphObjectInstance_show_self_get(PointerRNA *ptr)
 {
-  BLI_Iterator *iterator = ptr->data;
-  DEGObjectIterData *deg_iter = (DEGObjectIterData *)iterator->data;
-  int ob_visibility = BKE_object_visibility(iterator->current, deg_iter->eval_mode);
+  RNA_DepsgraphIterator *di = ptr->data;
+  DEGObjectIterData *deg_iter = (DEGObjectIterData *)di->iter.data;
+  int ob_visibility = BKE_object_visibility(di->iter.current, deg_iter->eval_mode);
   return (ob_visibility & OB_VISIBLE_SELF) != 0;
 }
 
 static bool rna_DepsgraphObjectInstance_show_particles_get(PointerRNA *ptr)
 {
-  BLI_Iterator *iterator = ptr->data;
-  DEGObjectIterData *deg_iter = (DEGObjectIterData *)iterator->data;
-  int ob_visibility = BKE_object_visibility(iterator->current, deg_iter->eval_mode);
+  RNA_DepsgraphIterator *di = ptr->data;
+  DEGObjectIterData *deg_iter = (DEGObjectIterData *)di->iter.data;
+  int ob_visibility = BKE_object_visibility(di->iter.current, deg_iter->eval_mode);
   return (ob_visibility & OB_VISIBLE_PARTICLES) != 0;
 }
 
 static PointerRNA rna_DepsgraphObjectInstance_parent_get(PointerRNA *ptr)
 {
-  BLI_Iterator *iterator = ptr->data;
-  DEGObjectIterData *deg_iter = (DEGObjectIterData *)iterator->data;
+  RNA_DepsgraphIterator *di = ptr->data;
+  DEGObjectIterData *deg_iter = (DEGObjectIterData *)di->iter.data;
   Object *dupli_parent = NULL;
   if (deg_iter->dupli_object_current != NULL) {
     dupli_parent = deg_iter->dupli_parent;
@@ -96,8 +114,8 @@ static PointerRNA rna_DepsgraphObjectInstance_parent_get(PointerRNA *ptr)
 
 static PointerRNA rna_DepsgraphObjectInstance_particle_system_get(PointerRNA *ptr)
 {
-  BLI_Iterator *iterator = ptr->data;
-  DEGObjectIterData *deg_iter = (DEGObjectIterData *)iterator->data;
+  RNA_DepsgraphIterator *di = ptr->data;
+  DEGObjectIterData *deg_iter = (DEGObjectIterData *)di->iter.data;
   struct ParticleSystem *particle_system = NULL;
   if (deg_iter->dupli_object_current != NULL) {
     particle_system = deg_iter->dupli_object_current->particle_system;
@@ -107,8 +125,8 @@ static PointerRNA rna_DepsgraphObjectInstance_particle_system_get(PointerRNA *pt
 
 static void rna_DepsgraphObjectInstance_persistent_id_get(PointerRNA *ptr, int *persistent_id)
 {
-  BLI_Iterator *iterator = ptr->data;
-  DEGObjectIterData *deg_iter = (DEGObjectIterData *)iterator->data;
+  RNA_DepsgraphIterator *di = ptr->data;
+  DEGObjectIterData *deg_iter = (DEGObjectIterData *)di->iter.data;
   if (deg_iter->dupli_object_current != NULL) {
     memcpy(persistent_id,
            deg_iter->dupli_object_current->persistent_id,
@@ -121,8 +139,8 @@ static void rna_DepsgraphObjectInstance_persistent_id_get(PointerRNA *ptr, int *
 
 static unsigned int rna_DepsgraphObjectInstance_random_id_get(PointerRNA *ptr)
 {
-  BLI_Iterator *iterator = ptr->data;
-  DEGObjectIterData *deg_iter = (DEGObjectIterData *)iterator->data;
+  RNA_DepsgraphIterator *di = ptr->data;
+  DEGObjectIterData *deg_iter = (DEGObjectIterData *)di->iter.data;
   if (deg_iter->dupli_object_current != NULL) {
     return deg_iter->dupli_object_current->random_id;
   }
@@ -133,23 +151,23 @@ static unsigned int rna_DepsgraphObjectInstance_random_id_get(PointerRNA *ptr)
 
 static void rna_DepsgraphObjectInstance_matrix_world_get(PointerRNA *ptr, float *mat)
 {
-  BLI_Iterator *iterator = ptr->data;
-  DEGObjectIterData *deg_iter = (DEGObjectIterData *)iterator->data;
+  RNA_DepsgraphIterator *di = ptr->data;
+  DEGObjectIterData *deg_iter = (DEGObjectIterData *)di->iter.data;
   if (deg_iter->dupli_object_current != NULL) {
     copy_m4_m4((float(*)[4])mat, deg_iter->dupli_object_current->mat);
   }
   else {
     /* We can return actual object's matrix here, no reason to return identity matrix
      * when this is not actually an instance... */
-    Object *ob = (Object *)iterator->current;
+    Object *ob = (Object *)di->iter.current;
     copy_m4_m4((float(*)[4])mat, ob->obmat);
   }
 }
 
 static void rna_DepsgraphObjectInstance_orco_get(PointerRNA *ptr, float *orco)
 {
-  BLI_Iterator *iterator = ptr->data;
-  DEGObjectIterData *deg_iter = (DEGObjectIterData *)iterator->data;
+  RNA_DepsgraphIterator *di = ptr->data;
+  DEGObjectIterData *deg_iter = (DEGObjectIterData *)di->iter.data;
   if (deg_iter->dupli_object_current != NULL) {
     copy_v3_v3(orco, deg_iter->dupli_object_current->orco);
   }
@@ -160,8 +178,8 @@ static void rna_DepsgraphObjectInstance_orco_get(PointerRNA *ptr, float *orco)
 
 static void rna_DepsgraphObjectInstance_uv_get(PointerRNA *ptr, float *uv)
 {
-  BLI_Iterator *iterator = ptr->data;
-  DEGObjectIterData *deg_iter = (DEGObjectIterData *)iterator->data;
+  RNA_DepsgraphIterator *di = ptr->data;
+  DEGObjectIterData *deg_iter = (DEGObjectIterData *)di->iter.data;
   if (deg_iter->dupli_object_current != NULL) {
     copy_v2_v2(uv, deg_iter->dupli_object_current->uv);
   }
@@ -321,7 +339,7 @@ static PointerRNA rna_Depsgraph_objects_get(CollectionPropertyIterator *iter)
  * so that previous one remains valid memory for python to access to. Yuck.
  */
 typedef struct RNA_Depsgraph_Instances_Iterator {
-  BLI_Iterator iterators[2];
+  RNA_DepsgraphIterator iterators[2];
   DEGObjectIterData deg_data[2];
   DupliObject dupli_object_current[2];
   int counter;
@@ -337,9 +355,9 @@ static void rna_Depsgraph_object_instances_begin(CollectionPropertyIterator *ite
   data->flag = DEG_ITER_OBJECT_FLAG_LINKED_DIRECTLY | DEG_ITER_OBJECT_FLAG_LINKED_VIA_SET |
                DEG_ITER_OBJECT_FLAG_VISIBLE | DEG_ITER_OBJECT_FLAG_DUPLI;
 
-  di_it->iterators[0].valid = true;
-  DEG_iterator_objects_begin(&di_it->iterators[0], data);
-  iter->valid = di_it->iterators[0].valid;
+  di_it->iterators[0].iter.valid = true;
+  DEG_iterator_objects_begin(&di_it->iterators[0].iter, data);
+  iter->valid = di_it->iterators[0].iter.valid;
 }
 
 static void rna_Depsgraph_object_instances_next(CollectionPropertyIterator *iter)
@@ -348,12 +366,12 @@ static void rna_Depsgraph_object_instances_next(CollectionPropertyIterator *iter
                                                 iter->internal.custom;
 
   /* We need to copy current iterator status to next one being worked on. */
-  di_it->iterators[(di_it->counter + 1) % 2] = di_it->iterators[di_it->counter % 2];
+  di_it->iterators[(di_it->counter + 1) % 2].iter = di_it->iterators[di_it->counter % 2].iter;
   di_it->deg_data[(di_it->counter + 1) % 2] = di_it->deg_data[di_it->counter % 2];
   di_it->counter++;
 
-  di_it->iterators[di_it->counter % 2].data = &di_it->deg_data[di_it->counter % 2];
-  DEG_iterator_objects_next(&di_it->iterators[di_it->counter % 2]);
+  di_it->iterators[di_it->counter % 2].iter.data = &di_it->deg_data[di_it->counter % 2];
+  DEG_iterator_objects_next(&di_it->iterators[di_it->counter % 2].iter);
   /* Dupli_object_current is also temp memory generated during the iterations,
    * it may be freed when last item has been iterated,
    * so we have same issue as with the iterator itself:
@@ -365,15 +383,24 @@ static void rna_Depsgraph_object_instances_next(CollectionPropertyIterator *iter
     di_it->deg_data[di_it->counter % 2].dupli_object_current =
         &di_it->dupli_object_current[di_it->counter % 2];
   }
-  iter->valid = di_it->iterators[di_it->counter % 2].valid;
+  iter->valid = di_it->iterators[di_it->counter % 2].iter.valid;
 }
 
 static void rna_Depsgraph_object_instances_end(CollectionPropertyIterator *iter)
 {
   RNA_Depsgraph_Instances_Iterator *di_it = (RNA_Depsgraph_Instances_Iterator *)
                                                 iter->internal.custom;
-  DEG_iterator_objects_end(&di_it->iterators[0]);
-  DEG_iterator_objects_end(&di_it->iterators[1]);
+  for (int i = 0; i < ARRAY_SIZE(di_it->iterators); i++) {
+    RNA_DepsgraphIterator *di = &di_it->iterators[i];
+    DEG_iterator_objects_end(&di->iter);
+
+#  ifdef WITH_PYTHON
+    if (di->py_instance) {
+      BPY_DECREF_RNA_INVALIDATE(di->py_instance);
+    }
+#  endif
+  }
+
   MEM_freeN(di_it);
 }
 
@@ -381,8 +408,8 @@ static PointerRNA rna_Depsgraph_object_instances_get(CollectionPropertyIterator
 {
   RNA_Depsgraph_Instances_Iterator *di_it = (RNA_Depsgraph_Instances_Iterator *)
                                                 iter->internal.custom;
-  BLI_Iterator *iterator = &di_it->iterators[di_it->counter % 2];
-  return rna_pointer_inherit_refine(&iter->parent, &RNA_DepsgraphObjectInstance, iterator);
+  RNA_DepsgraphIterator *di = &di_it->iterators[di_it->counter % 2];
+  return rna_pointer_inherit_refine(&iter->parent, &RNA_DepsgraphObjectInstance, di);
 }
 
 /* Iteration over evaluated IDs */
@@ -498,6 +525,10 @@ static void rna_def_depsgraph_instance(BlenderRNA *brna)
                          "Extended information about dependency graph object iterator "
                          "(Warning: All data here is 'evaluated' one, not original .blend IDs)");
 
+#  ifdef WITH_PYTHON
+  RNA_def_struct_register_funcs(srna, NULL, NULL, "rna_DepsgraphIterator_instance");
+#  endif
+
   prop = RNA_def_property(srna, "object", PROP_POINTER, PROP_NONE);
   RNA_def_property_struct_type(prop, "Object");
   RNA_def_property_ui_text(prop, "Object", "Evaluated object the iterator points to");
diff --git a/source/blender/python/intern/bpy_rna.c b/source/blender/python/intern/bpy_rna.c
index d9c004fb6fa..b22c5e60eb3 100644
--- a/source/blender/python/intern/bpy_rna.c
+++ b/source/blender/python/intern/bpy_rna.c
@@ -2213,6 +2213,26 @@ static int pyrna_prop_collection_bool(BPy_PropertyRNA *self)
   } \
   (void)0
 
+/**
+ * \param result: The result of calling a subscription operation on a collection (never NULL).
+ */
+static int pyrna_prop_collection_subscript_is_valid_or_error(const PyObject *value)
+{
+  if (value != Py_None) {
+    BLI_assert(BPy_StructRNA_Check(value));
+    const BPy_StructRNA *value_pyrna = (const BPy_StructRNA *)value;
+    if (UNLIKELY(value_pyrna->ptr.type == NULL)) {
+      /* It's important to use a `TypeError` as that is what's returned when `__getitem__` is
+       * called on an object that doesn't support item access. */
+      PyErr_Format(PyExc_TypeError,
+                   "'%.200s' object is not subscriptable (only iteration is supported)",
+                   Py_TYPE(value)->tp_name);
+      return -1;
+    }
+  }
+  return 0;
+}
+
 /* Internal use only. */
 static PyObject *pyrna_prop_collection_subscript_int(BPy_PropertyRNA *self, Py_ssize_t keynum)
 {
@@ -2223,8 +2243,35 @@ static PyObject *pyrna_prop_collection_subscript_int(BPy_PropertyRNA *self, Py_s
 
   PYRNA_PROP_COLLECTION_ABS_INDEX(NULL);
 
-  if (RNA_property_collection_lookup_int(&self->ptr, self->prop, keynum_abs, &newptr)) {
-    return pyrna_struct_CreatePyObject(&newptr);
+  if (RNA_property_collection_lookup_int_has_fn(self->prop)) {
+    if (RNA_property_collection_lookup_int(&self->ptr, self->prop, keynum_abs, &newptr)) {
+      return pyrna_struct_CreatePyObject(&newptr);
+    }
+  }
+  else {
+    /* No callback defined, just iterate and find the nth item. */
+    const int key = (int)keynum;
+    PyObject *result = NULL;
+    bool found = false;
+    CollectionPropertyIterator iter;
+    RNA_property_collection_begin(&self->ptr, self->prop, &iter);
+    for (int i = 0; iter.valid; RNA_property_collection_next(&iter), i++) {
+      if (i == key) {
+        result = pyrna_struct_CreatePyObject(&iter.ptr);
+        found = true;
+        break;
+      }
+    }
+    /* It's important to end the iterator after `result` has been created
+     * so iterators may optionally invalidate items that were iterated over, see: T100286. */
+    RNA_property_collection_end(&iter);
+    if (found) {
+      if (result && (pyrna_prop_collection_subscript_is_valid_or_error(result) == -1)) {
+        Py_DECREF(result);
+        result = NULL; /* The exception has been set. */
+      }
+      return result;
+    }
   }
 
   const int len = RNA_property_collection_length(&self->ptr, self->prop);
@@ -2306,8 +2353,45 @@ static PyObject *pyrna_prop_collection_subscript_str(BPy_PropertyRNA *self, cons
 
   PYRNA_PROP_CHECK_OBJ(self);
 
-  if (RNA_property_collection_lookup_string(&self->ptr, self->prop, keyname, &newptr)) {
-    return pyrna_struct_CreatePyObject(&newptr);
+  if (RNA_property_collection_lookup_string_has_fn(self->prop)) {
+    if (RNA_property_collection_lookup_string(&self->ptr, self->prop, keyname, &newptr)) {
+      return pyrna_struct_CreatePyObject(&newptr);
+    }
+  }
+  else {
+    /* No callback defined, just iterate and find the nth item. */
+    const int keylen = strlen(keyname);
+    char name[256];
+    int namelen;
+    PyObject *result = NULL;
+    bool found = false;
+    CollectionPropertyIterator iter;
+    RNA_property_collection_begin(&self->ptr, self->prop, &iter);
+    for (int i = 0; iter.valid; RNA_property_collection_next(&iter), i++) {
+      PropertyRNA *nameprop = RNA_struct_name_property(iter.ptr.type);
+      char *nameptr = RNA_property_string_get_alloc(
+          &iter.ptr, nameprop, name, sizeof(name), &namelen);
+      if ((keylen == namelen) && STREQ(nameptr, keyname)) {
+        found = true;
+      }
+      if ((char *)&name != nameptr) {
+        MEM_freeN(nameptr);
+      }
+      if (found) {
+        result = pyrna_struct_CreatePyObject(&iter.ptr);
+        break;
+      }
+    }
+    /* It's important to end the iterator after `result` has been created
+     * so iterators may optionally invalidate items that were iterated over, see: T100286. */
+    RNA_property_collection_end(&iter);
+    if (found) {
+      if (result && (pyrna_prop_collection_subscript_is_valid_or_error(result) == -1)) {
+        Py_DECREF(result);
+        result = NULL; /* The exception has been set. */
+      }
+      return result;
+    }
   }
 
   PyErr_Format(PyExc_KeyError, "bpy_prop_collection[key]: key \"%.200s\" not found", keyname);