From ee0e40331005cb5001bbf28bdfdce3be04666ffd Mon Sep 17 00:00:00 2001
From: Boris Zbarsky <bzbarsky@apple.com>
Date: Wed, 9 Jun 2021 15:54:26 -0400
Subject: [PATCH] Fix data race on mTestIndex. (#7494)

We could end up sending a message and getting a response to it before
we ever incremented mTestIndex (if our call into NextTest() was on a
thread other than the message thread).  If that happened, we would end
up running some subtest twice, and then later whenever we
incrememented mTestIndex would end up skipping some subtest.

Fixes https://github.com/project-chip/connectedhomeip/issues/7493
---
 examples/chip-tool/commands/tests/Commands.h  | 26 ++++++++++++-------
 .../templates/partials/test_cluster.zapt      | 13 ++++++----
 2 files changed, 24 insertions(+), 15 deletions(-)

diff --git a/examples/chip-tool/commands/tests/Commands.h b/examples/chip-tool/commands/tests/Commands.h
index 807a9bbe4e4f37..c8e5b1cd4aef23 100644
--- a/examples/chip-tool/commands/tests/Commands.h
+++ b/examples/chip-tool/commands/tests/Commands.h
@@ -24,7 +24,7 @@
 class TestCluster : public TestCommand
 {
 public:
-    TestCluster() : TestCommand("TestCluster") {}
+    TestCluster() : TestCommand("TestCluster"), mTestIndex(0) {}
 
     /////////// TestCommand Interface /////////
     CHIP_ERROR NextTest() override
@@ -37,7 +37,11 @@ class TestCluster : public TestCommand
             SetCommandExitStatus(true);
         }
 
-        switch (mTestIndex)
+        // Ensure we increment mTestIndex before we start running the relevant
+        // command.  That way if we lose the timeslice after we send the message
+        // but before our function call returns, we won't end up with an
+        // incorrect mTestIndex value observed when we get the response.
+        switch (mTestIndex++)
         {
         case 0:
             err = TestSendClusterTestClusterCommandTest_0();
@@ -55,7 +59,6 @@ class TestCluster : public TestCommand
             err = TestSendClusterTestClusterCommandReadAttribute_4();
             break;
         }
-        mTestIndex++;
 
         if (CHIP_NO_ERROR != err)
         {
@@ -67,8 +70,8 @@ class TestCluster : public TestCommand
     }
 
 private:
-    uint16_t mTestIndex = 0;
-    uint16_t mTestCount = 5;
+    std::atomic_uint16_t mTestIndex;
+    const uint16_t mTestCount = 5;
 
     //
     // Tests methods
@@ -437,7 +440,7 @@ class TestCluster : public TestCommand
 class OnOffCluster : public TestCommand
 {
 public:
-    OnOffCluster() : TestCommand("OnOffCluster") {}
+    OnOffCluster() : TestCommand("OnOffCluster"), mTestIndex(0) {}
 
     /////////// TestCommand Interface /////////
     CHIP_ERROR NextTest() override
@@ -450,7 +453,11 @@ class OnOffCluster : public TestCommand
             SetCommandExitStatus(true);
         }
 
-        switch (mTestIndex)
+        // Ensure we increment mTestIndex before we start running the relevant
+        // command.  That way if we lose the timeslice after we send the message
+        // but before our function call returns, we won't end up with an
+        // incorrect mTestIndex value observed when we get the response.
+        switch (mTestIndex++)
         {
         case 0:
             err = TestSendClusterOnOffCommandReadAttribute_0();
@@ -468,7 +475,6 @@ class OnOffCluster : public TestCommand
             err = TestSendClusterOnOffCommandReadAttribute_4();
             break;
         }
-        mTestIndex++;
 
         if (CHIP_NO_ERROR != err)
         {
@@ -480,8 +486,8 @@ class OnOffCluster : public TestCommand
     }
 
 private:
-    uint16_t mTestIndex = 0;
-    uint16_t mTestCount = 5;
+    std::atomic_uint16_t mTestIndex;
+    const uint16_t mTestCount = 5;
 
     //
     // Tests methods
diff --git a/examples/chip-tool/templates/partials/test_cluster.zapt b/examples/chip-tool/templates/partials/test_cluster.zapt
index 2a201787bb4525..5d461c438c043a 100644
--- a/examples/chip-tool/templates/partials/test_cluster.zapt
+++ b/examples/chip-tool/templates/partials/test_cluster.zapt
@@ -2,7 +2,7 @@
 class {{asCamelCased filename false}}: public TestCommand
 {
   public:
-    {{asCamelCased filename false}}(): TestCommand("{{filename}}") {}
+    {{asCamelCased filename false}}(): TestCommand("{{filename}}"), mTestIndex(0) {}
 
     /////////// TestCommand Interface /////////
     CHIP_ERROR NextTest() override
@@ -15,7 +15,11 @@ class {{asCamelCased filename false}}: public TestCommand
           SetCommandExitStatus(true);
       }
 
-      switch (mTestIndex)
+      // Ensure we increment mTestIndex before we start running the relevant
+      // command.  That way if we lose the timeslice after we send the message
+      // but before our function call returns, we won't end up with an
+      // incorrect mTestIndex value observed when we get the response.
+      switch (mTestIndex++)
       {
         {{#chip_tests_items}}
         case {{index}}:
@@ -23,7 +27,6 @@ class {{asCamelCased filename false}}: public TestCommand
           break;
         {{/chip_tests_items}}
       }
-      mTestIndex++;
 
       if (CHIP_NO_ERROR != err)
       {
@@ -36,8 +39,8 @@ class {{asCamelCased filename false}}: public TestCommand
 
 
   private:
-    uint16_t mTestIndex = 0;
-    uint16_t mTestCount = {{totalTests}};
+    std::atomic_uint16_t mTestIndex;
+    const uint16_t mTestCount = {{totalTests}};
 
     //
     // Tests methods