Index: Objects/fileobject.c
===================================================================
--- Objects/fileobject.c	(revision 62996)
+++ Objects/fileobject.c	(working copy)
@@ -864,6 +864,12 @@
 	off_t pos, end;
 	struct stat st;
 	if (fstat(fileno(f->f_fp), &st) == 0) {
+        /* if this isn't a regular file, then we can't trust st_size; in this
+         * case, return a very large number that will trigger an OverflowError
+         * in file_read; users must specify a buffer length in this case. */
+        if (!S_ISREG(st.st_mode))
+            return PY_SSIZE_T_MAX+1;
+
 		end = st.st_size;
 		/* The following is not a bug: we really need to call lseek()
 		   *and* ftell().  The reason is that some stdio libraries
@@ -966,6 +972,11 @@
 		}
 		if (bytesrequested < 0) {
 			buffersize = new_buffersize(f, buffersize);
+			if (buffersize > PY_SSIZE_T_MAX) {
+				PyErr_SetString(PyExc_OverflowError,
+	"unbounded read consumed more bytes than a Python string can hold");
+				return NULL;
+			}
 			if (_PyString_Resize(&v, buffersize) < 0)
 				return NULL;
 		} else {
Index: Lib/test/test_file.py
===================================================================
--- Lib/test/test_file.py	(revision 62996)
+++ Lib/test/test_file.py	(working copy)
@@ -134,6 +134,20 @@
                 f.close()
                 self.fail('%r is an invalid file mode' % mode)
 
+    def testDevZeroOverflow(self):
+        # /dev/zero is highly efficient at reading an unbounded number
+        # of bytes in modern linux kernels.  This unbounded reading from
+        # /dev/zero to not result in a MemoryError but instead trigger a
+        # OverflowError
+        if not os.path.exists('/dev/zero'):
+            return
+        try:
+            open('/dev/zero').read()
+            assert(0, 
+                   'Reading from /dev/zero unexpectedly returned successfully')
+        except OverflowError, err:
+            self.assertEquals(str(err), 'requested number of bytes is more than a Python string can hold')
+
     def testStdin(self):
         # This causes the interpreter to exit on OSF1 v5.1.
         if sys.platform != 'osf1V5':