Issue #22290: Fix error handling in the _posixsubprocess module.

* Don't call the garbage collector with an exception set: it causes an
  assertion to fail in debug mode.
* Enhance also error handling if allocating an array for the executable list
  failed.
* Add an unit test for 4 different errors in the _posixsubprocess module.

Lib/test/test_subprocess.py

@@ -2216,6 +2216,39 @@ class POSIXProcessTestCase(BaseTestCase):
 
         self.assertNotIn(fd, remaining_fds)
 
+    @support.cpython_only
+    def test_fork_exec(self):
+        # Issue #22290: fork_exec() must not crash on memory allocation failure
+        # or other errors
+        import _posixsubprocess
+        gc_enabled = gc.isenabled()
+        try:
+            # Use a preexec function and enable the garbage collector
+            # to force fork_exec() to re-enable the garbage collector
+            # on error.
+            func = lambda: None
+            gc.enable()
+
+            executable_list = "exec"   # error: must be a sequence
+
+            for args, exe_list, cwd, env_list in (
+                (123,      [b"exe"], None, [b"env"]),
+                ([b"arg"], 123,      None, [b"env"]),
+                ([b"arg"], [b"exe"], 123,  [b"env"]),
+                ([b"arg"], [b"exe"], None, 123),
+            ):
+                with self.assertRaises(TypeError):
+                    _posixsubprocess.fork_exec(
+                        args, exe_list,
+                        True, [], cwd, env_list,
+                        -1, -1, -1, -1,
+                        1, 2, 3, 4,
+                        True, True, func)
+        finally:
+            if not gc_enabled:
+                gc.disable()
+
+
 
 @unittest.skipUnless(mswindows, "Windows specific tests")
 class Win32ProcessTestCase(BaseTestCase):