From 796509b66d8245b2051f3c5dde642ff177f7b155 Mon Sep 17 00:00:00 2001
From: "Mark D. Roth" <roth@google.com>
Date: Mon, 10 Sep 2018 13:11:34 -0700
Subject: [PATCH] Fix ubsan error in subchannel_list code.

---
 .../lb_policy/pick_first/pick_first.cc        | 11 +++++----
 .../lb_policy/round_robin/round_robin.cc      | 11 +++++----
 .../lb_policy/subchannel_list.h               | 24 ++++++++++++-------
 3 files changed, 27 insertions(+), 19 deletions(-)

diff --git a/src/core/ext/filters/client_channel/lb_policy/pick_first/pick_first.cc b/src/core/ext/filters/client_channel/lb_policy/pick_first/pick_first.cc
index 602d6e92f98..ed8cc60ea1c 100644
--- a/src/core/ext/filters/client_channel/lb_policy/pick_first/pick_first.cc
+++ b/src/core/ext/filters/client_channel/lb_policy/pick_first/pick_first.cc
@@ -71,11 +71,12 @@ class PickFirst : public LoadBalancingPolicy {
       : public SubchannelData<PickFirstSubchannelList,
                               PickFirstSubchannelData> {
    public:
-    PickFirstSubchannelData(PickFirstSubchannelList* subchannel_list,
-                            const grpc_lb_user_data_vtable* user_data_vtable,
-                            const grpc_lb_address& address,
-                            grpc_subchannel* subchannel,
-                            grpc_combiner* combiner)
+    PickFirstSubchannelData(
+        SubchannelList<PickFirstSubchannelList, PickFirstSubchannelData>*
+            subchannel_list,
+        const grpc_lb_user_data_vtable* user_data_vtable,
+        const grpc_lb_address& address, grpc_subchannel* subchannel,
+        grpc_combiner* combiner)
         : SubchannelData(subchannel_list, user_data_vtable, address, subchannel,
                          combiner) {}
 
diff --git a/src/core/ext/filters/client_channel/lb_policy/round_robin/round_robin.cc b/src/core/ext/filters/client_channel/lb_policy/round_robin/round_robin.cc
index 4195c1e9d1a..8dd5820bae8 100644
--- a/src/core/ext/filters/client_channel/lb_policy/round_robin/round_robin.cc
+++ b/src/core/ext/filters/client_channel/lb_policy/round_robin/round_robin.cc
@@ -89,11 +89,12 @@ class RoundRobin : public LoadBalancingPolicy {
       : public SubchannelData<RoundRobinSubchannelList,
                               RoundRobinSubchannelData> {
    public:
-    RoundRobinSubchannelData(RoundRobinSubchannelList* subchannel_list,
-                             const grpc_lb_user_data_vtable* user_data_vtable,
-                             const grpc_lb_address& address,
-                             grpc_subchannel* subchannel,
-                             grpc_combiner* combiner)
+    RoundRobinSubchannelData(
+        SubchannelList<RoundRobinSubchannelList, RoundRobinSubchannelData>*
+            subchannel_list,
+        const grpc_lb_user_data_vtable* user_data_vtable,
+        const grpc_lb_address& address, grpc_subchannel* subchannel,
+        grpc_combiner* combiner)
         : SubchannelData(subchannel_list, user_data_vtable, address, subchannel,
                          combiner),
           user_data_vtable_(user_data_vtable),
diff --git a/src/core/ext/filters/client_channel/lb_policy/subchannel_list.h b/src/core/ext/filters/client_channel/lb_policy/subchannel_list.h
index d87de510829..5e8682e056a 100644
--- a/src/core/ext/filters/client_channel/lb_policy/subchannel_list.h
+++ b/src/core/ext/filters/client_channel/lb_policy/subchannel_list.h
@@ -65,6 +65,10 @@ class MySubchannelList
 
 namespace grpc_core {
 
+// Forward declaration.
+template <typename SubchannelListType, typename SubchannelDataType>
+class SubchannelList;
+
 // Stores data for a particular subchannel in a subchannel list.
 // Callers must create a subclass that implements the
 // ProcessConnectivityChangeLocked() method.
@@ -72,7 +76,9 @@ template <typename SubchannelListType, typename SubchannelDataType>
 class SubchannelData {
  public:
   // Returns a pointer to the subchannel list containing this object.
-  SubchannelListType* subchannel_list() const { return subchannel_list_; }
+  SubchannelListType* subchannel_list() const {
+    return static_cast<SubchannelListType*>(subchannel_list_);
+  }
 
   // Returns the index into the subchannel list of this object.
   size_t Index() const {
@@ -133,10 +139,11 @@ class SubchannelData {
   GRPC_ABSTRACT_BASE_CLASS
 
  protected:
-  SubchannelData(SubchannelListType* subchannel_list,
-                 const grpc_lb_user_data_vtable* user_data_vtable,
-                 const grpc_lb_address& address, grpc_subchannel* subchannel,
-                 grpc_combiner* combiner);
+  SubchannelData(
+      SubchannelList<SubchannelListType, SubchannelDataType>* subchannel_list,
+      const grpc_lb_user_data_vtable* user_data_vtable,
+      const grpc_lb_address& address, grpc_subchannel* subchannel,
+      grpc_combiner* combiner);
 
   virtual ~SubchannelData();
 
@@ -161,7 +168,7 @@ class SubchannelData {
   static void OnConnectivityChangedLocked(void* arg, grpc_error* error);
 
   // Backpointer to owning subchannel list.  Not owned.
-  SubchannelListType* subchannel_list_;
+  SubchannelList<SubchannelListType, SubchannelDataType>* subchannel_list_;
 
   // The subchannel and connected subchannel.
   grpc_subchannel* subchannel_;
@@ -268,7 +275,7 @@ class SubchannelList
 
 template <typename SubchannelListType, typename SubchannelDataType>
 SubchannelData<SubchannelListType, SubchannelDataType>::SubchannelData(
-    SubchannelListType* subchannel_list,
+    SubchannelList<SubchannelListType, SubchannelDataType>* subchannel_list,
     const grpc_lb_user_data_vtable* user_data_vtable,
     const grpc_lb_address& address, grpc_subchannel* subchannel,
     grpc_combiner* combiner)
@@ -532,8 +539,7 @@ SubchannelList<SubchannelListType, SubchannelDataType>::SubchannelList(
               address_uri);
       gpr_free(address_uri);
     }
-    subchannels_.emplace_back(static_cast<SubchannelListType*>(this),
-                              addresses->user_data_vtable,
+    subchannels_.emplace_back(this, addresses->user_data_vtable,
                               addresses->addresses[i], subchannel, combiner);
   }
 }