From e13d1d9dda8c27691180bc618bd5e9bf43dfa89f Mon Sep 17 00:00:00 2001
From: Pablo Galindo Salgado <Pablogsal@gmail.com>
Date: Sun, 20 Nov 2022 20:20:03 +0000
Subject: [PATCH] gh-99581: Fix a buffer overflow in the tokenizer when copying
 lines that fill the available buffer (#99605)

---
 Lib/test/test_tokenize.py                        | 16 ++++++++++++++++
 ...2022-11-19-22-27-52.gh-issue-99581.yKYPbf.rst |  3 +++
 Parser/tokenizer.c                               |  7 ++++++-
 3 files changed, 25 insertions(+), 1 deletion(-)
 create mode 100644 Misc/NEWS.d/next/Core and Builtins/2022-11-19-22-27-52.gh-issue-99581.yKYPbf.rst

diff --git a/Lib/test/test_tokenize.py b/Lib/test/test_tokenize.py
index 47f2c06685b..63c2501cfe2 100644
--- a/Lib/test/test_tokenize.py
+++ b/Lib/test/test_tokenize.py
@@ -10,6 +10,8 @@ from textwrap import dedent
 from unittest import TestCase, mock
 from test.test_grammar import (VALID_UNDERSCORE_LITERALS,
                                INVALID_UNDERSCORE_LITERALS)
+from test.support import os_helper
+from test.support.script_helper import run_test_script, make_script
 import os
 import token
 
@@ -2631,5 +2633,19 @@ async def f():
         self.assertEqual(get_tokens(code), get_tokens(code_no_cont))
 
 
+class CTokenizerBufferTests(unittest.TestCase):
+    def test_newline_at_the_end_of_buffer(self):
+        # See issue 99581: Make sure that if we need to add a new line at the
+        # end of the buffer, we have enough space in the buffer, specially when
+        # the current line is as long as the buffer space available.
+        test_script = f"""\
+        #coding: latin-1
+        #{"a"*10000}
+        #{"a"*10002}"""
+        with os_helper.temp_dir() as temp_dir:
+            file_name = make_script(temp_dir, 'foo', test_script)
+            run_test_script(file_name)
+
+
 if __name__ == "__main__":
     unittest.main()
diff --git a/Misc/NEWS.d/next/Core and Builtins/2022-11-19-22-27-52.gh-issue-99581.yKYPbf.rst b/Misc/NEWS.d/next/Core and Builtins/2022-11-19-22-27-52.gh-issue-99581.yKYPbf.rst
new file mode 100644
index 00000000000..8071fd130dd
--- /dev/null
+++ b/Misc/NEWS.d/next/Core and Builtins/2022-11-19-22-27-52.gh-issue-99581.yKYPbf.rst	
@@ -0,0 +1,3 @@
+Fixed a bug that was causing a buffer overflow if the tokenizer copies a
+line missing the newline caracter from a file that is as long as the
+available tokenizer buffer. Patch by Pablo galindo
diff --git a/Parser/tokenizer.c b/Parser/tokenizer.c
index f2131cf39b3..ce72e152902 100644
--- a/Parser/tokenizer.c
+++ b/Parser/tokenizer.c
@@ -413,7 +413,11 @@ tok_readline_recode(struct tok_state *tok) {
         error_ret(tok);
         goto error;
     }
-    if (!tok_reserve_buf(tok, buflen + 1)) {
+    // Make room for the null terminator *and* potentially
+    // an extra newline character that we may need to artificially
+    // add.
+    size_t buffer_size = buflen + 2;
+    if (!tok_reserve_buf(tok, buffer_size)) {
         goto error;
     }
     memcpy(tok->inp, buf, buflen);
@@ -1000,6 +1004,7 @@ tok_underflow_file(struct tok_state *tok) {
         return 0;
     }
     if (tok->inp[-1] != '\n') {
+        assert(tok->inp + 1 < tok->end);
         /* Last line does not end in \n, fake one */
         *tok->inp++ = '\n';
         *tok->inp = '\0';