Issue #9611, #9015: FileIO.read(), FileIO.readinto(), FileIO.write() and

os.write() clamp the length to INT_MAX on Windows.

Misc/NEWS

@@ -9,6 +9,9 @@ What's New in Python 2.7.3?
 Core and Builtins
 -----------------
 
+- Issue #9611, #9015: FileIO.read(), FileIO.readinto(), FileIO.write() and
+  os.write() clamp the length to INT_MAX on Windows.
+
 - Issue #1195: my_fgets() now always clears errors before calling fgets(). Fix
   the following case: sys.stdin.read() stopped with CTRL+d (end of file),
   raw_input() interrupted by CTRL+c.

Modules/_io/fileio.c

@@ -474,7 +474,7 @@ static PyObject *
 fileio_readinto(fileio *self, PyObject *args)
 {
     Py_buffer pbuf;
-    Py_ssize_t n;
+    Py_ssize_t n, len;
 
     if (self->fd < 0)
         return err_closed();
@@ -485,9 +485,16 @@ fileio_readinto(fileio *self, PyObject *args)
         return NULL;
 
     if (_PyVerify_fd(self->fd)) {
+        len = pbuf.len;
         Py_BEGIN_ALLOW_THREADS
         errno = 0;
-        n = read(self->fd, pbuf.buf, pbuf.len);
+#if defined(MS_WIN64) || defined(MS_WINDOWS)
+        if (len > INT_MAX)
+            len = INT_MAX;
+        n = read(self->fd, pbuf.buf, (int)len);
+#else
+        n = read(self->fd, pbuf.buf, len);
+#endif
         Py_END_ALLOW_THREADS
     } else
         n = -1;
@@ -620,6 +627,10 @@ fileio_read(fileio *self, PyObject *args)
         return fileio_readall(self);
     }
 
+#if defined(MS_WIN64) || defined(MS_WINDOWS)
+    if (size > INT_MAX)
+        size = INT_MAX;
+#endif
     bytes = PyBytes_FromStringAndSize(NULL, size);
     if (bytes == NULL)
         return NULL;
@@ -628,7 +639,11 @@ fileio_read(fileio *self, PyObject *args)
     if (_PyVerify_fd(self->fd)) {
         Py_BEGIN_ALLOW_THREADS
         errno = 0;
+#if defined(MS_WIN64) || defined(MS_WINDOWS)
+        n = read(self->fd, ptr, (int)size);
+#else
         n = read(self->fd, ptr, size);
+#endif
         Py_END_ALLOW_THREADS
     } else
         n = -1;
@@ -655,7 +670,7 @@ static PyObject *
 fileio_write(fileio *self, PyObject *args)
 {
     Py_buffer pbuf;
-    Py_ssize_t n;
+    Py_ssize_t n, len;
 
     if (self->fd < 0)
         return err_closed();
@@ -668,7 +683,14 @@ fileio_write(fileio *self, PyObject *args)
     if (_PyVerify_fd(self->fd)) {
         Py_BEGIN_ALLOW_THREADS
         errno = 0;
-        n = write(self->fd, pbuf.buf, pbuf.len);
+        len = pbuf.len;
+#if defined(MS_WIN64) || defined(MS_WINDOWS)
+        if (len > INT_MAX)
+            len = INT_MAX;
+        n = write(self->fd, pbuf.buf, (int)len);
+#else
+        n = write(self->fd, pbuf.buf, len);
+#endif
         Py_END_ALLOW_THREADS
     } else
         n = -1;

Modules/posixmodule.c

@@ -3903,7 +3903,7 @@ posix_getgroups(PyObject *self, PyObject *noargs)
 #endif
     gid_t grouplist[MAX_GROUPS];
 
-    /* On MacOSX getgroups(2) can return more than MAX_GROUPS results 
+    /* On MacOSX getgroups(2) can return more than MAX_GROUPS results
      * This is a helper variable to store the intermediate result when
      * that happens.
      *
@@ -6648,7 +6648,7 @@ posix_write(PyObject *self, PyObject *args)
 {
     Py_buffer pbuf;
     int fd;
-    Py_ssize_t size;
+    Py_ssize_t size, len;
 
     if (!PyArg_ParseTuple(args, "is*:write", &fd, &pbuf))
         return NULL;
@@ -6656,8 +6656,15 @@ posix_write(PyObject *self, PyObject *args)
         PyBuffer_Release(&pbuf);
         return posix_error();
     }
+    len = pbuf.len;
     Py_BEGIN_ALLOW_THREADS
-    size = write(fd, pbuf.buf, (size_t)pbuf.len);
+#if defined(MS_WIN64) || defined(MS_WINDOWS)
+    if (len > INT_MAX)
+        len = INT_MAX;
+    size = write(fd, pbuf.buf, (int)len);
+#else
+    size = write(fd, pbuf.buf, len);
+#endif
     Py_END_ALLOW_THREADS
     PyBuffer_Release(&pbuf);
     if (size < 0)