Fixed memory bug: properly root repeated/map field when assigning. (#8639)

* Fixed memory bug: properly root repeated/map field when assigning.

Previously the protobuf extension would not properly root
memory from a repeated field or map when assigning to a
message field (see the attached test case).  This could cause
crashes if the repeated field is subsequently accessed.

* Add accidentally-deleted Ruby test.

ruby/ext/google/protobuf_c/map.c

@@ -167,7 +167,8 @@ VALUE Map_deep_copy(VALUE obj) {
                             new_arena_rb);
 }
 
-const upb_map* Map_GetUpbMap(VALUE val, const upb_fielddef *field) {
+const upb_map* Map_GetUpbMap(VALUE val, const upb_fielddef* field,
+                             upb_arena* arena) {
   const upb_fielddef* key_field = map_field_key(field);
   const upb_fielddef* value_field = map_field_value(field);
   TypeInfo value_type_info = TypeInfo_get(value_field);
@@ -189,6 +190,7 @@ const upb_map* Map_GetUpbMap(VALUE val, const upb_fielddef *field) {
     rb_raise(cTypeError, "Map value type has wrong message/enum class");
   }
 
+  Arena_fuse(self->arena, arena);
   return self->map;
 }
 
@@ -236,7 +238,7 @@ static VALUE Map_merge_into_self(VALUE _self, VALUE hashmap) {
     upb_msg *self_msg = Map_GetMutable(_self);
     size_t iter = UPB_MAP_BEGIN;
 
-    upb_arena_fuse(arena, Arena_get(other->arena));
+    Arena_fuse(other->arena, arena);
 
     if (self->key_type != other->key_type ||
         self->value_type_info.type != other->value_type_info.type ||
@@ -511,7 +513,7 @@ static VALUE Map_dup(VALUE _self) {
   upb_arena *arena = Arena_get(new_self->arena);
   upb_map *new_map = Map_GetMutable(new_map_rb);
 
-  upb_arena_fuse(arena, Arena_get(self->arena));
+  Arena_fuse(self->arena, arena);
 
   while (upb_mapiter_next(self->map, &iter)) {
     upb_msgval key = upb_mapiter_key(self->map, iter);

ruby/ext/google/protobuf_c/map.h

@@ -44,7 +44,8 @@ VALUE Map_GetRubyWrapper(upb_map *map, upb_fieldtype_t key_type,
 // Gets the underlying upb_map for this Ruby map object, which must have
 // key/value type that match |field|. If this is not a map or the type doesn't
 // match, raises an exception.
-const upb_map *Map_GetUpbMap(VALUE val, const upb_fielddef *field);
+const upb_map *Map_GetUpbMap(VALUE val, const upb_fielddef *field,
+                             upb_arena *arena);
 
 // Implements #inspect for this map by appending its contents to |b|.
 void Map_Inspect(StringBuilder *b, const upb_map *map, upb_fieldtype_t key_type,

ruby/ext/google/protobuf_c/message.c

@@ -277,9 +277,9 @@ static void Message_setfield(upb_msg* msg, const upb_fielddef* f, VALUE val,
                              upb_arena* arena) {
   upb_msgval msgval;
   if (upb_fielddef_ismap(f)) {
-    msgval.map_val = Map_GetUpbMap(val, f);
+    msgval.map_val = Map_GetUpbMap(val, f, arena);
   } else if (upb_fielddef_isseq(f)) {
-    msgval.array_val = RepeatedField_GetUpbArray(val, f);
+    msgval.array_val = RepeatedField_GetUpbArray(val, f, arena);
   } else {
     if (val == Qnil &&
         (upb_fielddef_issubmsg(f) || upb_fielddef_realcontainingoneof(f))) {
@@ -660,7 +660,7 @@ static VALUE Message_dup(VALUE _self) {
   // TODO(copy unknown fields?)
   // TODO(use official upb msg copy function)
   memcpy((upb_msg*)new_msg_self->msg, self->msg, size);
-  upb_arena_fuse(Arena_get(new_msg_self->arena), Arena_get(self->arena));
+  Arena_fuse(self->arena, Arena_get(new_msg_self->arena));
   return new_msg;
 }
 
@@ -1314,7 +1314,7 @@ const upb_msg* Message_GetUpbMessage(VALUE value, const upb_msgdef* m,
   }
 
   Message* self = ruby_to_Message(value);
-  upb_arena_fuse(arena, Arena_get(self->arena));
+  Arena_fuse(self->arena, arena);
 
   return self->msg;
 }

ruby/ext/google/protobuf_c/protobuf.c

@@ -204,6 +204,16 @@ upb_arena *Arena_get(VALUE _arena) {
   return arena->arena;
 }
 
+void Arena_fuse(VALUE _arena, upb_arena *other) {
+  Arena *arena;
+  TypedData_Get_Struct(_arena, Arena, &Arena_type, arena);
+  if (!upb_arena_fuse(arena->arena, other)) {
+    rb_raise(rb_eRuntimeError,
+             "Unable to fuse arenas. This should never happen since Ruby does "
+             "not use initial blocks");
+  }
+}
+
 VALUE Arena_new() {
   return Arena_alloc(cArena);
 }

ruby/ext/google/protobuf_c/protobuf.h

@@ -55,6 +55,10 @@ const upb_fielddef* map_field_value(const upb_fielddef* field);
 VALUE Arena_new();
 upb_arena *Arena_get(VALUE arena);
 
+// Fuses this arena to another, throwing a Ruby exception if this is not
+// possible.
+void Arena_fuse(VALUE arena, upb_arena *other);
+
 // Pins this Ruby object to the lifetime of this arena, so that as long as the
 // arena is alive this object will not be collected.
 //

ruby/ext/google/protobuf_c/repeated_field.c

@@ -149,7 +149,8 @@ VALUE RepeatedField_deep_copy(VALUE _self) {
   return new_rptfield;
 }
 
-const upb_array* RepeatedField_GetUpbArray(VALUE val, const upb_fielddef *field) {
+const upb_array* RepeatedField_GetUpbArray(VALUE val, const upb_fielddef* field,
+                                           upb_arena* arena) {
   RepeatedField* self;
   TypeInfo type_info = TypeInfo_get(field);
 
@@ -167,6 +168,7 @@ const upb_array* RepeatedField_GetUpbArray(VALUE val, const upb_fielddef *field)
     rb_raise(cTypeError, "Repeated field array has wrong message/enum class");
   }
 
+  Arena_fuse(self->arena, arena);
   return self->array;
 }
 
@@ -412,7 +414,7 @@ static VALUE RepeatedField_dup(VALUE _self) {
   int size = upb_array_size(self->array);
   int i;
 
-  upb_arena_fuse(arena, Arena_get(self->arena));
+  Arena_fuse(self->arena, arena);
 
   for (i = 0; i < size; i++) {
     upb_msgval msgval = upb_array_get(self->array, i);

ruby/ext/google/protobuf_c/repeated_field.h

@@ -44,7 +44,8 @@ VALUE RepeatedField_GetRubyWrapper(upb_array* msg, TypeInfo type_info,
 // Gets the underlying upb_array for this Ruby RepeatedField object, which must
 // have a type that matches |f|. If this is not a repeated field or the type
 // doesn't match, raises an exception.
-const upb_array* RepeatedField_GetUpbArray(VALUE value, const upb_fielddef* f);
+const upb_array* RepeatedField_GetUpbArray(VALUE value, const upb_fielddef* f,
+                                           upb_arena* arena);
 
 // Implements #inspect for this repeated field by appending its contents to |b|.
 void RepeatedField_Inspect(StringBuilder* b, const upb_array* array,

ruby/tests/basic.rb

@@ -63,6 +63,13 @@ module BasicTest
       end
     end
 
+    def test_issue_8559_crash
+      msg = TestMessage.new
+      msg.repeated_int32 = ::Google::Protobuf::RepeatedField.new(:int32, [1, 2, 3])
+      GC.start(full_mark: true, immediate_sweep: true)
+      TestMessage.encode(msg)
+    end
+
     def test_has_field
       m = TestSingularFields.new
       assert !m.has_singular_msg?