bpo-1621: Avoid signed integer overflow in set_table_resize(). (GH-9059) (GH-9199)

Address a C undefined behavior signed integer overflow issue in set object table resizing.  Our -fwrapv compiler flag and practical reasons why sets are unlikely to get this large should mean this was never an issue but it was incorrect code that generates code analysis warnings.

(cherry picked from commit 6c7d67ce83a62b5f0fe5c53a6df602827451bf7f)

Co-authored-by: Sergey Fedoseev <fedoseev.sergey@gmail.com>

diff --git a/Misc/NEWS.d/next/Core and Builtins/2018-09-11-15-19-37.bpo-1621.7o19yG.rst b/Misc/NEWS.d/next/Core and Builtins/2018-09-11-15-19-37.bpo-1621.7o19yG.rst
new file mode 100644 (file)
index 0000000..4047ff3
--- /dev/null
+++ b/Misc/NEWS.d/next/Core and Builtins/2018-09-11-15-19-37.bpo-1621.7o19yG.rst
@@ -0,0 +1,2 @@
+Do not assume signed integer overflow behavior (C undefined behavior) when
+performing set hash table resizing.

diff --git a/Objects/setobject.c b/Objects/setobject.c
index 96485f83ecb63208c3749dcfb714db4c60f4f5c8..27836c0fb1ea2898744526ee96a9a1eb5a813c37 100644 (file)
--- a/Objects/setobject.c
+++ b/Objects/setobject.c
@@ -294,7 +294,6 @@ actually be smaller than the old one.
 static int
 set_table_resize(PySetObject *so, Py_ssize_t minused)
 {
-    Py_ssize_t newsize;
     setentry *oldtable, *newtable, *entry;
     Py_ssize_t oldfill = so->fill;
     Py_ssize_t oldused = so->used;
@@ -307,13 +306,9 @@ set_table_resize(PySetObject *so, Py_ssize_t minused)
 
     /* Find the smallest table size > minused. */
     /* XXX speed-up with intrinsics */
-    for (newsize = PySet_MINSIZE;
-         newsize <= minused && newsize > 0;
-         newsize <<= 1)
-        ;
-    if (newsize <= 0) {
-        PyErr_NoMemory();
-        return -1;
+    size_t newsize = PySet_MINSIZE;
+    while (newsize <= (size_t)minused) {
+        newsize <<= 1; // The largest possible value is PY_SSIZE_T_MAX + 1.
     }
 
     /* Get space for a new table. */