Merge pull request #2061 from Amanieu/fix_indices

Avoid UB in PySlice::indices

CHANGELOG.md

@@ -49,6 +49,7 @@ and this project adheres to [Semantic Versioning](https://semver.org/spec/v2.0.0
 - Fix undefined symbol for `PyObject_HasAttr` on PyPy. [#2025](https://github.com/PyO3/pyo3/pull/2025)
 - Fix memory leak in `PyErr::into_value`. [#2026](https://github.com/PyO3/pyo3/pull/2026)
 - Fix clippy warning `needless-option-as-deref` in code generated by `#[pyfunction]` and `#[pymethods]`. [#2040](https://github.com/PyO3/pyo3/pull/2040)
+- Fix undefined behavior in `PySlice::indices`. [#2061](https://github.com/PyO3/pyo3/pull/2061)
 
 ## [0.15.1] - 2021-11-19
 

src/types/slice.rs

@@ -57,17 +57,17 @@ impl PySlice {
     pub fn indices(&self, length: c_long) -> PyResult<PySliceIndices> {
         // non-negative Py_ssize_t should always fit into Rust usize
         unsafe {
-            let slicelength: isize = 0;
-            let start: isize = 0;
-            let stop: isize = 0;
-            let step: isize = 0;
+            let mut slicelength: isize = 0;
+            let mut start: isize = 0;
+            let mut stop: isize = 0;
+            let mut step: isize = 0;
             let r = ffi::PySlice_GetIndicesEx(
                 self.as_ptr(),
                 length as Py_ssize_t,
-                &start as *const _ as *mut _,
-                &stop as *const _ as *mut _,
-                &step as *const _ as *mut _,
-                &slicelength as *const _ as *mut _,
+                &mut start,
+                &mut stop,
+                &mut step,
+                &mut slicelength,
             );
             if r == 0 {
                 Ok(PySliceIndices {