From: Miss Islington (bot) <31488909+miss-islington@users.noreply.github.com>
Date: Tue, 13 Sep 2022 15:03:40 +0000 (-0700)
Subject: gh-96678: Fix UB of null pointer arithmetic (GH-96782)
X-Git-Tag: v3.11.1~488
X-Git-Url: http://git.ipfire.org/?a=commitdiff_plain;h=f2d7fa88390502fa408b8f1e1ad1b6d23a04c48a;p=thirdparty%2FPython%2Fcpython.git

gh-96678: Fix UB of null pointer arithmetic (GH-96782)


Automerge-Triggered-By: GH:pablogsal
(cherry picked from commit 81e36f350b75d2ed2668825f7df6e059b57f859c)

Co-authored-by: Matthias Görgens <matthias.goergens@gmail.com>
---

diff --git a/Misc/NEWS.d/next/Core and Builtins/2022-09-13-12-06-46.gh-issue-96678.NqGFyb.rst b/Misc/NEWS.d/next/Core and Builtins/2022-09-13-12-06-46.gh-issue-96678.NqGFyb.rst
new file mode 100644
index 000000000000..bdd33c8d2ca9
--- /dev/null
+++ b/Misc/NEWS.d/next/Core and Builtins/2022-09-13-12-06-46.gh-issue-96678.NqGFyb.rst	
@@ -0,0 +1 @@
+Fix undefined behaviour in C code of null pointer arithmetic.
diff --git a/Parser/tokenizer.c b/Parser/tokenizer.c
index 8d9fbf5cf959..a5cfb659b430 100644
--- a/Parser/tokenizer.c
+++ b/Parser/tokenizer.c
@@ -1542,7 +1542,7 @@ tok_get(struct tok_state *tok, const char **p_start, const char **p_end)
     } while (c == ' ' || c == '\t' || c == '\014');
 
     /* Set start of current token */
-    tok->start = tok->cur - 1;
+    tok->start = tok->cur == NULL ? NULL : tok->cur - 1;
 
     /* Skip comment, unless it's a type comment */
     if (c == '#') {