gh-102701: Fix overflow in dictobject.c (GH-102750)

Author: methane

Lib/test/test_bigmem.py

@@ -1248,6 +1248,15 @@ def test_sort(self, size):
         self.assertEqual(l[-10:], [5] * 10)
 
 
+class DictTest(unittest.TestCase):
+
+    @bigmemtest(size=357913941, memuse=160)
+    def test_dict(self, size):
+        # https://github.com/python/cpython/issues/102701
+        d = dict.fromkeys(range(size))
+        d[size] = 1
+
+
 if __name__ == '__main__':
     if len(sys.argv) > 1:
         support.set_memlimit(sys.argv[1])

Misc/NEWS.d/next/Core and Builtins/2023-03-16-17-24-44.gh-issue-102701.iNGVaS.rst

@@ -0,0 +1 @@
+Fix overflow when creating very large dict.

Objects/dictobject.c

@@ -596,7 +596,7 @@ new_keys_object(PyInterpreterState *interp, uint8_t log2_size, bool unicode)
 
     assert(log2_size >= PyDict_LOG_MINSIZE);
 
-    usable = USABLE_FRACTION(1<<log2_size);
+    usable = USABLE_FRACTION((size_t)1<<log2_size);
     if (log2_size < 8) {
         log2_bytes = log2_size;
     }