http://bugs.python.org/issue5544

Guard _fileio.c against other malicious os.close(f.fileno()) attempts.
Add tests to test_fileio.py to verify behaviour.

Lib/test/test_fileio.py

@@ -6,6 +6,7 @@ import errno
 import unittest
 from array import array
 from weakref import proxy
+from functools import wraps
 
 from test.support import (TESTFN, findfile, check_warnings, run_unittest,
                           make_bad_fd)
@@ -114,20 +115,106 @@ class AutoFileTests(unittest.TestCase):
         else:
             self.fail("Should have raised IOError")
 
-    def testErrnoOnClose(self):
-        # Test that the IOError's `errno` attribute is correctly set when
-        # close() fails. Here we first close the file descriptor ourselves so
-        # that close() fails with EBADF ('Bad file descriptor').
+    #A set of functions testing that we get expected behaviour if someone has
+    #manually closed the internal file descriptor.  First, a decorator:
+    def ClosedFD(func):
+        @wraps(func)
+        def wrapper(self):
+            #forcibly close the fd before invoking the problem function
             f = self.f
             os.close(f.fileno())
-        self.f = None
             try:
-            f.close()
+                func(self, f)
+            finally:
+                try:
+                    self.f.close()
+                except IOError:
+                    pass
+        return wrapper
+
+    def ClosedFDRaises(func):
+        @wraps(func)
+        def wrapper(self):
+            #forcibly close the fd before invoking the problem function
+            f = self.f
+            os.close(f.fileno())
+            try:
+                func(self, f)
             except IOError as e:
                 self.assertEqual(e.errno, errno.EBADF)
             else:
                 self.fail("Should have raised IOError")
+            finally:
+                try:
+                    self.f.close()
+                except IOError:
+                    pass
+        return wrapper
 
+    @ClosedFDRaises
+    def testErrnoOnClose(self, f):
+        f.close()
+
+    @ClosedFDRaises
+    def testErrnoOnClosedWrite(self, f):
+        f.write('a')
+
+    @ClosedFDRaises
+    def testErrnoOnClosedSeek(self, f):
+        f.seek(0)
+
+    @ClosedFDRaises
+    def testErrnoOnClosedTell(self, f):
+        f.tell()
+
+    @ClosedFDRaises
+    def testErrnoOnClosedTruncate(self, f):
+        f.truncate(0)
+
+    @ClosedFD
+    def testErrnoOnClosedSeekable(self, f):
+        f.seekable()
+
+    @ClosedFD
+    def testErrnoOnClosedReadable(self, f):
+        f.readable()
+
+    @ClosedFD
+    def testErrnoOnClosedWritable(self, f):
+        f.writable()
+
+    @ClosedFD
+    def testErrnoOnClosedFileno(self, f):
+        f.fileno()
+
+    @ClosedFD
+    def testErrnoOnClosedIsatty(self, f):
+        self.assertEqual(f.isatty(), False)
+
+    def ReopenForRead(self):
+        try:
+            self.f.close()
+        except IOError:
+            pass
+        self.f = _FileIO(TESTFN, 'r')
+        os.close(self.f.fileno())
+        return self.f
+
+    @ClosedFDRaises
+    def testErrnoOnClosedRead(self, f):
+        f = self.ReopenForRead()
+        f.read(1)
+
+    @ClosedFDRaises
+    def testErrnoOnClosedReadall(self, f):
+        f = self.ReopenForRead()
+        f.readall()
+
+    @ClosedFDRaises
+    def testErrnoOnClosedReadinto(self, f):
+        f = self.ReopenForRead()
+        a = array('b', b'x'*10)
+        f.readinto(a)
 
 class OtherFileTests(unittest.TestCase):
 

Modules/_fileio.c

@@ -475,10 +475,13 @@ fileio_readinto(PyFileIOObject *self, PyObject *args)
 	if (!PyArg_ParseTuple(args, "w*", &pbuf))
 		return NULL;
 
+	if (_PyVerify_fd(self->fd)) {
 		Py_BEGIN_ALLOW_THREADS
 		errno = 0;
 		n = read(self->fd, pbuf.buf, pbuf.len);
 		Py_END_ALLOW_THREADS
+	} else
+		n = -1;
 	PyBuffer_Release(&pbuf);
 	if (n < 0) {
 		if (errno == EAGAIN)
@@ -522,6 +525,9 @@ fileio_readall(PyFileIOObject *self)
 	Py_ssize_t total = 0;
 	int n;
 
+	if (!_PyVerify_fd(self->fd))
+		return PyErr_SetFromErrno(PyExc_IOError);
+
 	result = PyBytes_FromStringAndSize(NULL, SMALLCHUNK);
 	if (result == NULL)
 		return NULL;
@@ -596,10 +602,13 @@ fileio_read(PyFileIOObject *self, PyObject *args)
 		return NULL;
 	ptr = PyBytes_AS_STRING(bytes);
 
+	if (_PyVerify_fd(self->fd)) {
 		Py_BEGIN_ALLOW_THREADS
 		errno = 0;
 		n = read(self->fd, ptr, size);
 		Py_END_ALLOW_THREADS
+	} else
+		n = -1;
 
 	if (n < 0) {
 		if (errno == EAGAIN)
@@ -632,10 +641,13 @@ fileio_write(PyFileIOObject *self, PyObject *args)
 	if (!PyArg_ParseTuple(args, "s*", &pbuf))
 		return NULL;
 
+	if (_PyVerify_fd(self->fd)) {
 		Py_BEGIN_ALLOW_THREADS
 		errno = 0;
 		n = write(self->fd, pbuf.buf, pbuf.len);
 		Py_END_ALLOW_THREADS
+	} else
+		n = -1;
 
 	PyBuffer_Release(&pbuf);
 
@@ -688,6 +700,7 @@ portable_lseek(int fd, PyObject *posobj, int whence)
 			return NULL;
 	}
 
+	if (_PyVerify_fd(fd)) {
 		Py_BEGIN_ALLOW_THREADS
 #if defined(MS_WIN64) || defined(MS_WINDOWS)
 		res = _lseeki64(fd, pos, whence);
@@ -695,6 +708,8 @@ portable_lseek(int fd, PyObject *posobj, int whence)
 		res = lseek(fd, pos, whence);
 #endif
 		Py_END_ALLOW_THREADS
+	} else
+		res = -1;
 	if (res < 0)
 		return PyErr_SetFromErrno(PyExc_IOError);
 
@@ -757,13 +772,15 @@ fileio_truncate(PyFileIOObject *self, PyObject *args)
 		/* Move to the position to be truncated. */
                 posobj = portable_lseek(fd, posobj, 0);
         }
+	if (posobj == NULL)
+		return NULL;
 
 #if defined(HAVE_LARGEFILE_SUPPORT)
 	pos = PyLong_AsLongLong(posobj);
 #else
 	pos = PyLong_AsLong(posobj);
 #endif
-	if (PyErr_Occurred())
+	if (pos == -1 && PyErr_Occurred())
 		return NULL;
 
 #ifdef MS_WINDOWS