From: Stan Ulbrych <89152624+StanFromIreland@users.noreply.github.com>
Date: Tue, 10 Mar 2026 16:57:34 +0000 (+0000)
Subject: Fix integer overflow for formats "s" and "p" in the struct module (GH-145750)
X-Git-Tag: v3.15.0a8~367
X-Git-Url: http://git.ipfire.org/gitweb.cgi?a=commitdiff_plain;h=4d0dce0c8ddc4d0321bd590a1a33990edc2e1b08;p=thirdparty%2FPython%2Fcpython.git

Fix integer overflow for formats "s" and "p" in the struct module (GH-145750)
---

diff --git a/Lib/test/test_struct.py b/Lib/test/test_struct.py
index 6904572d095d..55e2ce590a25 100644
--- a/Lib/test/test_struct.py
+++ b/Lib/test/test_struct.py
@@ -555,6 +555,12 @@ class StructTest(ComplexesAreIdenticalMixin, unittest.TestCase):
         hugecount3 = '{}i{}q'.format(sys.maxsize // 4, sys.maxsize // 8)
         self.assertRaises(struct.error, struct.calcsize, hugecount3)
 
+        hugecount4 = '{}?s'.format(sys.maxsize)
+        self.assertRaises(struct.error, struct.calcsize, hugecount4)
+
+        hugecount5 = '{}?p'.format(sys.maxsize)
+        self.assertRaises(struct.error, struct.calcsize, hugecount5)
+
     def test_trailing_counter(self):
         store = array.array('b', b' '*100)
 
diff --git a/Misc/NEWS.d/next/Library/2026-03-10-14-13-12.gh-issue-145750.iQsTeX.rst b/Misc/NEWS.d/next/Library/2026-03-10-14-13-12.gh-issue-145750.iQsTeX.rst
new file mode 100644
index 000000000000..a909bea2caff
--- /dev/null
+++ b/Misc/NEWS.d/next/Library/2026-03-10-14-13-12.gh-issue-145750.iQsTeX.rst
@@ -0,0 +1,3 @@
+Avoid undefined behaviour from signed integer overflow when parsing format
+strings in the :mod:`struct` module. Found by OSS Fuzz in
+:oss-fuzz:`488466741`.
diff --git a/Modules/_struct.c b/Modules/_struct.c
index c2f7b1fe0e80..f8574322b40c 100644
--- a/Modules/_struct.c
+++ b/Modules/_struct.c
@@ -1676,7 +1676,13 @@ prepare_s(PyStructObject *self, PyObject *format)
 
         switch (c) {
             case 's': _Py_FALLTHROUGH;
-            case 'p': len++; ncodes++; break;
+            case 'p':
+                if (len == PY_SSIZE_T_MAX) {
+                    goto overflow;
+                }
+                len++;
+                ncodes++;
+                break;
             case 'x': break;
             default:
                 if (num > PY_SSIZE_T_MAX - len) {