From fae8f4a9cb88a68eb14750cbb8ddf8740fd67b8b Mon Sep 17 00:00:00 2001
From: Nir Soffer <nirsof@gmail.com>
Date: Fri, 7 Jul 2017 09:10:46 +0300
Subject: [PATCH] bpo-29854: Fix segfault in call_readline() (GH-728)

If history-length is set in .inputrc, and the history file is double the
history size (or more), history_get(N) returns NULL, and python
segfaults. Fix that by checking for NULL return value.

It seems that the root cause is incorrect handling of bigger history in
readline, but Python should not segfault even if readline returns
unexpected value.

This issue affects only GNU readline. When using libedit emulation
system history size option does not work.
---
 Lib/test/test_readline.py                     | 43 +++++++++++++++++--
 .../2017-07-07-02-18-57.bpo-29854.J8wKb_.rst  |  2 +
 Modules/readline.c                            | 10 +++--
 3 files changed, 48 insertions(+), 7 deletions(-)
 create mode 100644 Misc/NEWS.d/next/Library/2017-07-07-02-18-57.bpo-29854.J8wKb_.rst

diff --git a/Lib/test/test_readline.py b/Lib/test/test_readline.py
index 06a9149374a..cc3001a3796 100644
--- a/Lib/test/test_readline.py
+++ b/Lib/test/test_readline.py
@@ -9,7 +9,7 @@ import subprocess
 import sys
 import tempfile
 import unittest
-from test.support import import_module, unlink, TESTFN
+from test.support import import_module, unlink, temp_dir, TESTFN
 from test.support.script_helper import assert_python_ok
 
 # Skip tests if there is no readline module
@@ -210,13 +210,50 @@ print("history", ascii(readline.get_history_item(1)))
         self.assertIn(b"result " + expected + b"\r\n", output)
         self.assertIn(b"history " + expected + b"\r\n", output)
 
+    @unittest.skipIf(is_editline,
+                     "editline history size configuration is broken")
+    def test_history_size(self):
+        history_size = 10
+        with temp_dir() as test_dir:
+            inputrc = os.path.join(test_dir, "inputrc")
+            with open(inputrc, "wb") as f:
+                f.write(b"set history-size %d\n" % history_size)
 
-def run_pty(script, input=b"dummy input\r"):
+            history_file = os.path.join(test_dir, "history")
+            with open(history_file, "wb") as f:
+                # history_size * 2 items crashes readline
+                data = b"".join(b"item %d\n" % i
+                                for i in range(history_size * 2))
+                f.write(data)
+
+            script = """
+import os
+import readline
+
+history_file = os.environ["HISTORY_FILE"]
+readline.read_history_file(history_file)
+input()
+readline.write_history_file(history_file)
+"""
+
+            env = dict(os.environ)
+            env["INPUTRC"] = inputrc
+            env["HISTORY_FILE"] = history_file
+
+            run_pty(script, input=b"last input\r", env=env)
+
+            with open(history_file, "rb") as f:
+                lines = f.readlines()
+            self.assertEqual(len(lines), history_size)
+            self.assertEqual(lines[-1].strip(), b"last input")
+
+
+def run_pty(script, input=b"dummy input\r", env=None):
     pty = import_module('pty')
     output = bytearray()
     [master, slave] = pty.openpty()
     args = (sys.executable, '-c', script)
-    proc = subprocess.Popen(args, stdin=slave, stdout=slave, stderr=slave)
+    proc = subprocess.Popen(args, stdin=slave, stdout=slave, stderr=slave, env=env)
     os.close(slave)
     with ExitStack() as cleanup:
         cleanup.enter_context(proc)
diff --git a/Misc/NEWS.d/next/Library/2017-07-07-02-18-57.bpo-29854.J8wKb_.rst b/Misc/NEWS.d/next/Library/2017-07-07-02-18-57.bpo-29854.J8wKb_.rst
new file mode 100644
index 00000000000..5c439087dcb
--- /dev/null
+++ b/Misc/NEWS.d/next/Library/2017-07-07-02-18-57.bpo-29854.J8wKb_.rst
@@ -0,0 +1,2 @@
+Fix segfault in readline when using readline's history-size option.  Patch
+by Nir Soffer.
diff --git a/Modules/readline.c b/Modules/readline.c
index dfbbb292f66..6ba124742a3 100644
--- a/Modules/readline.c
+++ b/Modules/readline.c
@@ -1347,15 +1347,17 @@ call_readline(FILE *sys_stdin, FILE *sys_stdout, const char *prompt)
     if (should_auto_add_history && n > 0) {
         const char *line;
         int length = _py_get_history_length();
-        if (length > 0)
+        if (length > 0) {
+            HIST_ENTRY *hist_ent;
 #ifdef __APPLE__
             if (using_libedit_emulation) {
                 /* handle older 0-based or newer 1-based indexing */
-                line = (const char *)history_get(length + libedit_history_start - 1)->line;
+                hist_ent = history_get(length + libedit_history_start - 1);
             } else
 #endif /* __APPLE__ */
-            line = (const char *)history_get(length)->line;
-        else
+                hist_ent = history_get(length);
+            line = hist_ent ? hist_ent->line : "";
+        } else
             line = "";
         if (strcmp(p, line))
             add_history(p);