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

miss-islington · matthiasgoergens · web-flow · commit f2d7fa883905 · 2022-09-13T08:03:40.000-07:00
Automerge-Triggered-By: GH:pablogsal (cherry picked from commit 81e36f3) 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
@@ -0,0 +1 @@
+Fix undefined behaviour in C code of null pointer arithmetic.
diff --git 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 == '#') {

Original file line number	Diff line number	Diff line change
`@@ -0,0 +1 @@`
	`1`	`+Fix undefined behaviour in C code of null pointer arithmetic.`