Merge pull request #8964 from juliantaylor/empty-read

BUG: don't create array with invalid memory in where

3 files changed, 22 insertions, 1 deletions

diff --git a/numpy/core/src/multiarray/item_selection.c b/numpy/core/src/multiarray/item_selection.c
index 3c0f0782e..c88cdfdcb 100644
--- a/numpy/core/src/multiarray/item_selection.c
+++ b/numpy/core/src/multiarray/item_selection.c
@@ -2176,6 +2176,7 @@ PyArray_Nonzero(PyArrayObject *self)
     NpyIter_IterNextFunc *iternext;
     NpyIter_GetMultiIndexFunc *get_multi_index;
     char **dataptr;
+    int is_empty = 0;
 
     /*
      * First count the number of non-zeros in 'self'.
@@ -2329,13 +2330,22 @@ finish:
         return NULL;
     }
 
+    for (i = 0; i < ndim; ++i) {
+        if (PyArray_DIMS(ret)[i] == 0) {
+            is_empty = 1;
+            break;
+        }
+    }
+
     /* Create views into ret, one for each dimension */
     for (i = 0; i < ndim; ++i) {
         npy_intp stride = ndim * NPY_SIZEOF_INTP;
+        /* the result is an empty array, the view must point to valid memory */
+        npy_intp data_offset = is_empty ? 0 : i * NPY_SIZEOF_INTP;
 
         PyArrayObject *view = (PyArrayObject *)PyArray_New(Py_TYPE(ret), 1,
                                     &nonzero_count, NPY_INTP, &stride,
-                                    PyArray_BYTES(ret) + i*NPY_SIZEOF_INTP,
+                                    PyArray_BYTES(ret) + data_offset,
                                     0, PyArray_FLAGS(ret), (PyObject *)ret);
         if (view == NULL) {
             Py_DECREF(ret);
diff --git a/numpy/core/src/multiarray/lowlevel_strided_loops.c.src b/numpy/core/src/multiarray/lowlevel_strided_loops.c.src
index 9a5c3004d..397aaf209 100644
--- a/numpy/core/src/multiarray/lowlevel_strided_loops.c.src
+++ b/numpy/core/src/multiarray/lowlevel_strided_loops.c.src
@@ -206,6 +206,9 @@ static NPY_GCC_OPT_3 void
 #else
     npy_uint64 temp0, temp1;
 #endif
+    if (N == 0) {
+        return;
+    }
 #if @is_aligned@ && @elsize@ != 16
     /* sanity check */
     assert(npy_is_aligned(dst, _ALIGN(@type@)));
diff --git a/numpy/core/tests/test_multiarray.py b/numpy/core/tests/test_multiarray.py
index 3f4b183aa..4dc82eb1d 100644
--- a/numpy/core/tests/test_multiarray.py
+++ b/numpy/core/tests/test_multiarray.py
@@ -6547,6 +6547,14 @@ class TestWhere(TestCase):
         assert_equal(np.where(True, a, b), "abcd")
         assert_equal(np.where(False, b, a), "abcd")
 
+    def test_empty_result(self):
+        # pass empty where result through an assignment which reads the data of
+        # empty arrays, error detectable with valgrind, see gh-8922
+        x = np.zeros((1, 1))
+        ibad = np.vstack(np.where(x == 99.))
+        assert_array_equal(ibad,
+                           np.atleast_2d(np.array([[],[]], dtype=np.intp)))
+
 
 if not IS_PYPY:
     # sys.getsizeof() is not valid on PyPy