From 8c5f554406a63ceafa2829ec6b5b36260883b9a3 Mon Sep 17 00:00:00 2001
From: Ben Kurtovic <ben.kurtovic@gmail.com>
Date: Tue, 14 May 2019 23:51:21 -0400
Subject: [PATCH] Add guard against a rare crash in the C tokenizer

---
 CHANGELOG                                      | 5 +++--
 docs/changelog.rst                             | 5 +++--
 mwparserfromhell/parser/ctokenizer/tok_parse.c | 6 ++++++
 3 files changed, 12 insertions(+), 4 deletions(-)

diff --git a/CHANGELOG b/CHANGELOG
index 918c37f..a37680d 100644
--- a/CHANGELOG
+++ b/CHANGELOG
@@ -1,6 +1,7 @@
-v0.6 (unreleased):
+v0.5.4 (unreleased):
 
-- ...
+- Fixed an unlikely crash in the C tokenizer when interrupted while parsing
+  a heading.
 
 v0.5.3 (released March 30, 2019):
 
diff --git a/docs/changelog.rst b/docs/changelog.rst
index a18c7f8..bb81c42 100644
--- a/docs/changelog.rst
+++ b/docs/changelog.rst
@@ -1,13 +1,14 @@
 Changelog
 =========
 
-v0.6
+v0.5.4
 ----
 
 Unreleased
 (`changes <https://github.com/earwig/mwparserfromhell/compare/v0.5.3...develop>`__):
 
-- ...
+- Fixed an unlikely crash in the C tokenizer when interrupted while parsing
+  a heading.
 
 v0.5.3
 ------
diff --git a/mwparserfromhell/parser/ctokenizer/tok_parse.c b/mwparserfromhell/parser/ctokenizer/tok_parse.c
index ab46252..c32e48c 100644
--- a/mwparserfromhell/parser/ctokenizer/tok_parse.c
+++ b/mwparserfromhell/parser/ctokenizer/tok_parse.c
@@ -813,6 +813,9 @@ static int Tokenizer_parse_heading(Tokenizer* self)
         self->global ^= GL_HEADING;
         return 0;
     }
+    if (!heading) {
+        return -1;
+    }
 #ifdef IS_PY3K
     level = PyLong_FromSsize_t(heading->level);
 #else
@@ -892,6 +895,9 @@ static HeadingData* Tokenizer_handle_heading_end(Tokenizer* self)
         self->head = reset + best - 1;
     }
     else {
+        if (!after) {
+            return NULL;
+        }
         for (i = 0; i < best; i++) {
             if (Tokenizer_emit_char(self, '=')) {
                 Py_DECREF(after->title);