Prevent writing to thread/fiber-local variables from another thread

lib/drb/extservm.rb

@@ -87,7 +87,7 @@ def invoke_service_command(name, command)
         pid = spawn("#{command} #{uri} #{name}")
       end
       th = Process.detach(pid)
-      th[:drb_service] = name
+      # th[:drb_service] = name
       th
     end
   end

process.c

@@ -1093,11 +1093,13 @@ detach_process_watcher(void *arg)
     return rb_last_status_get();
 }
 
+VALUE rb_thread_local_aset_no_check(VALUE thread, ID id, VALUE val);
+
 VALUE
 rb_detach_process(rb_pid_t pid)
 {
     VALUE watcher = rb_thread_create(detach_process_watcher, (void*)(VALUE)pid);
-    rb_thread_local_aset(watcher, id_pid, PIDT2NUM(pid));
+    rb_thread_local_aset_no_check(watcher, id_pid, PIDT2NUM(pid));
     RBASIC_SET_CLASS(watcher, rb_cWaiter);
     return watcher;
 }

test/ruby/test_fiber.rb

@@ -169,6 +169,13 @@ def tvar(var, val)
     assert_equal(nil, Thread.current[:v]);
   end
 
+  def test_inter_thread_tls
+    t = Thread.new { }
+    assert_raise(ThreadError) do
+      t[:foo] = "bar"
+    end
+  end
+
   def test_alive
     fib = Fiber.new{Fiber.yield}
     assert_equal(true, fib.alive?)

test/ruby/test_thread.rb

@@ -108,6 +108,13 @@ def test_thread_variable_frozen
     end
   end
 
+  def test_inter_thread_variable
+    t = Thread.new { }
+    assert_raise(ThreadError) do
+      t.thread_variable_set(:foo, "bar")
+    end
+  end
+
   def test_mutex_synchronize
     m = Thread::Mutex.new
     r = 0

thread.c

@@ -3149,6 +3149,20 @@ rb_thread_local_aset(VALUE thread, ID id, VALUE val)
 	rb_error_frozen("thread locals");
     }
 
+    if (thread != GET_THREAD()->self) {
+        rb_raise(rb_eThreadError, "inter-thread access of TLS prohibited");
+    }
+
+    return threadptr_local_aset(rb_thread_ptr(thread), id, val);
+}
+
+VALUE
+rb_thread_local_aset_no_check(VALUE thread, ID id, VALUE val)
+{
+    if (OBJ_FROZEN(thread)) {
+	rb_error_frozen("thread locals");
+    }
+
     return threadptr_local_aset(rb_thread_ptr(thread), id, val);
 }
 
@@ -3226,6 +3240,10 @@ rb_thread_variable_set(VALUE thread, VALUE id, VALUE val)
 	rb_error_frozen("thread locals");
     }
 
+    if (thread != GET_THREAD()->self) {
+        rb_raise(rb_eThreadError, "inter-thread access of TLS prohibited");
+    }
+
     locals = rb_ivar_get(thread, id_locals);
     return rb_hash_aset(locals, rb_to_symbol(id), val);
 }