Check the dimension of runtime shapes given to xtensor

The shape of an xtensor<T, N> is a std::array<std::size_t, N>. resize()
checks that a runtime shape has N values, but from_shape() only had an
XTENSOR_ASSERT, off in release builds, and reshape() had no check. A
shape of the wrong length was copied past the std::array, a
stack-buffer-overflow, as in
xtensor<double, 1>::from_shape(std::vector<std::size_t>{2, 3}).

interp() builds its xtensor<T, 1> result with from_shape(x.shape()), so
a 2-D x overflowed the same way, and a 0-D x gave a result with an
uninitialized shape. It also read a 2-D xp or a short fp out of bounds.

from_shape() and both reshape() overloads now use the same
XTENSOR_PRECONDITION as resize(). interp() checks up front that x, xp
and fp are 1-D, that xp is not empty and that fp has the length of xp.

This removes the GCC 13 and 15 -Warray-bounds and -Wmaybe-uninitialized
warnings on the copy into the shape in from_shape(), reached from
interp() in test_extended_xmath_interp.

Author: gouarin

include/xtensor/containers/xcontainer.hpp

@@ -1091,6 +1091,10 @@ namespace xt
     template <class S>
     inline auto& xstrided_container<D>::reshape(S&& shape, layout_type layout) &
     {
+        XTENSOR_PRECONDITION(
+            detail::check_resize_dimension(m_shape, shape),
+            "cannot change the number of dimensions of xtensor"
+        );
         reshape_impl(
             std::forward<S>(shape),
             xtl::is_signed<std::decay_t<typename std::decay_t<S>::value_type>>(),
@@ -1103,6 +1107,10 @@ namespace xt
     template <class T>
     inline auto& xstrided_container<D>::reshape(std::initializer_list<T> shape, layout_type layout) &
     {
+        XTENSOR_PRECONDITION(
+            detail::check_resize_dimension(m_shape, shape),
+            "cannot change the number of dimensions of xtensor"
+        );
         using sh_type = rebind_container_t<T, shape_type>;
         sh_type sh = xtl::make_sequence<sh_type>(shape.size());
         std::copy(shape.begin(), shape.end(), sh.begin());

include/xtensor/containers/xtensor.hpp

@@ -543,7 +543,7 @@ namespace xt
     template <class S>
     inline xtensor_container<EC, N, L, Tag> xtensor_container<EC, N, L, Tag>::from_shape(S&& s)
     {
-        XTENSOR_ASSERT_MSG(s.size() == N, "Cannot change dimension of xtensor.");
+        XTENSOR_PRECONDITION(s.size() == N, "cannot change the number of dimensions of xtensor");
         shape_type shape = xtl::forward_sequence<shape_type, S>(s);
         return self_type(shape);
     }

include/xtensor/core/xmath.hpp

@@ -2966,6 +2966,27 @@ namespace xt
         return eval(sum(trap, {saxis}));
     }
 
+    namespace detail
+    {
+        // The result is a one-dimensional xtensor built from the shape of x, and
+        // xp and fp are read at the indices found in xp.
+        template <class E1, class E2, class E3>
+        inline void check_interp_arguments(const E1& x, const E2& xp, const E3& fp)
+        {
+            if (x.dimension() != 1 || xp.dimension() != 1 || fp.dimension() != 1)
+            {
+                XTENSOR_THROW(std::runtime_error, "interp: x, xp and fp must be one-dimensional.");
+            }
+            if (xp.size() == 0 || fp.size() != xp.size())
+            {
+                XTENSOR_THROW(
+                    std::runtime_error,
+                    "interp: xp must not be empty and fp must have the length of xp."
+                );
+            }
+        }
+    }
+
     /**
      * @ingroup basic_functions
      * @brief Returns the one-dimensional piecewise linear interpolant to a function with given discrete data
@@ -2985,7 +3006,7 @@ namespace xt
         using value_type = typename E3::value_type;
 
         // basic checks
-        XTENSOR_ASSERT(xp.dimension() == 1);
+        detail::check_interp_arguments(x, xp, fp);
         XTENSOR_ASSERT(std::is_sorted(x.cbegin(), x.cend()));
         XTENSOR_ASSERT(std::is_sorted(xp.cbegin(), xp.cend()));
 
@@ -3146,6 +3167,7 @@ namespace xt
     template <class E1, class E2, class E3>
     inline auto interp(const E1& x, const E2& xp, const E3& fp)
     {
+        detail::check_interp_arguments(x, xp, fp);
         return interp(x, xp, fp, fp[0], fp[fp.size() - 1]);
     }
 

test/test_xmath.cpp

@@ -903,6 +903,27 @@ namespace xt
         }
     }
 
+    TEST(xmath, interp_invalid_arguments)
+    {
+        xt::xarray<double> xp = {0.0, 1.0, 3.0};
+        xt::xarray<double> fp = {0.0, 1.0, 3.0};
+        xt::xarray<double> x = {0.5, 2.0};
+        xt::xarray<double> x2 = {{0.5, 1.5}, {2.0, 2.5}};
+        xt::xarray<double> empty = xt::xarray<double>::from_shape({0});
+        xt::xarray<double> fp_short = {0.0, 1.0};
+
+        XT_EXPECT_THROW(xt::interp(x2, xp, fp), std::runtime_error);
+        XT_EXPECT_THROW(xt::interp(x, x2, fp), std::runtime_error);
+        XT_EXPECT_THROW(xt::interp(x, xp, x2), std::runtime_error);
+        XT_EXPECT_THROW(xt::interp(x, empty, empty), std::runtime_error);
+        XT_EXPECT_THROW(xt::interp(x, xp, fp_short), std::runtime_error);
+        XT_EXPECT_THROW(xt::interp(x, xp, fp_short, 0.0, 1.0), std::runtime_error);
+
+        auto f = xt::interp(x, xp, fp);
+        EXPECT_EQ(f(0), 0.5);
+        EXPECT_EQ(f(1), 2.0);
+    }
+
     TEST(xmath, cov)
     {
         xt::xarray<double> x = {0.0, 1.0, 2.0};

test/test_xtensor.cpp

@@ -233,6 +233,23 @@ namespace xt
         test_throwing_reshape(b);
     }
 
+    TEST(xtensor, change_dimension)
+    {
+        // The shape of an xtensor holds exactly N values.
+        xtensor<int, 1> a = xt::arange(6);
+        XT_EXPECT_THROW(a.reshape({2, 3}), std::runtime_error);
+        XT_EXPECT_THROW(a.reshape(std::vector<std::size_t>{2, 3}), std::runtime_error);
+        XT_EXPECT_THROW(a.reshape(std::vector<int>{2, -1}), std::runtime_error);
+        XT_EXPECT_THROW(a.resize(std::vector<std::size_t>{2, 3}), std::runtime_error);
+        EXPECT_EQ(a.shape()[0], 6u);
+
+        using shape = std::vector<std::size_t>;
+        XT_EXPECT_THROW((xtensor<int, 1>::from_shape(shape{2, 3})), std::runtime_error);
+        XT_EXPECT_THROW((xtensor<int, 2>::from_shape(shape{6})), std::runtime_error);
+        XT_EXPECT_THROW((xtensor<int, 2>::from_shape(shape{})), std::runtime_error);
+        EXPECT_EQ((xtensor<int, 2>::from_shape(shape{2, 3}).size()), 6u);
+    }
+
     TEST(xtensor, transpose)
     {
         xtensor_dynamic a;