[3.6] bpo-30730: Prevent environment variables injection in subprocess on Windows. (GH-2325) (#2360)

Prevent passing other invalid environment variables and command arguments..
(cherry picked from commit d174d24a5d)

Lib/test/test_subprocess.py

@@ -644,6 +644,46 @@ class ProcessTestCase(BaseTestCase):
                  # environment
                  b"['__CF_USER_TEXT_ENCODING']"))
 
+    def test_invalid_cmd(self):
+        # null character in the command name
+        cmd = sys.executable + '\0'
+        with self.assertRaises(ValueError):
+            subprocess.Popen([cmd, "-c", "pass"])
+
+        # null character in the command argument
+        with self.assertRaises(ValueError):
+            subprocess.Popen([sys.executable, "-c", "pass#\0"])
+
+    def test_invalid_env(self):
+        # null character in the enviroment variable name
+        newenv = os.environ.copy()
+        newenv["FRUIT\0VEGETABLE"] = "cabbage"
+        with self.assertRaises(ValueError):
+            subprocess.Popen([sys.executable, "-c", "pass"], env=newenv)
+
+        # null character in the enviroment variable value
+        newenv = os.environ.copy()
+        newenv["FRUIT"] = "orange\0VEGETABLE=cabbage"
+        with self.assertRaises(ValueError):
+            subprocess.Popen([sys.executable, "-c", "pass"], env=newenv)
+
+        # equal character in the enviroment variable name
+        newenv = os.environ.copy()
+        newenv["FRUIT=ORANGE"] = "lemon"
+        with self.assertRaises(ValueError):
+            subprocess.Popen([sys.executable, "-c", "pass"], env=newenv)
+
+        # equal character in the enviroment variable value
+        newenv = os.environ.copy()
+        newenv["FRUIT"] = "orange=lemon"
+        with subprocess.Popen([sys.executable, "-c",
+                               'import sys, os;'
+                               'sys.stdout.write(os.getenv("FRUIT"))'],
+                              stdout=subprocess.PIPE,
+                              env=newenv) as p:
+            stdout, stderr = p.communicate()
+            self.assertEqual(stdout, b"orange=lemon")
+
     def test_communicate_stdin(self):
         p = subprocess.Popen([sys.executable, "-c",
                               'import sys;'