VRT expressions: enable array bounds-checking

OSGeo · Nov 12, 2024 · fd94c9e · fd94c9e
1 parent 9698635
commit fd94c9e
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Showing 2 changed files with 50 additions and 1 deletion.
diff --git a/autotest/gdrivers/vrtprocesseddataset.py b/autotest/gdrivers/vrtprocesseddataset.py
@@ -1271,6 +1271,19 @@ def test_vrtprocesseddataset_trimming_errors(tmp_vsimem):
             "must return a vector or a list of scalars",
             id="return wrong number of bands",
         ),
+        pytest.param(
+            """
+             var out[3];
+             for (var i := 0; i < 100; i += 1) {
+                out[i] := i;
+             }
+             return [out];
+             """,
+            np.array([[[1, 2]], [[3, 4]], [[5, 6]]]),
+            np.array([[[1, 1]], [[2, 2]], [[3, 3]]]),
+            "Attempted to access index 3",
+            id="out of bounds vector access",
+        ),
     ],
 )
 def test_vrtprocesseddataset_expression(tmp_vsimem, expression, src, expected, error):

diff --git a/frmts/vrt/vrtexpression.cpp b/frmts/vrt/vrtexpression.cpp
@@ -8,6 +8,27 @@
 #define exprtk_disable_string_capabilities
 #include <exprtk.hpp>
 
+#include <sstream>
+
+struct vector_access_check final : public exprtk::vector_access_runtime_check
+{
+    bool handle_runtime_violation(violation_context &context) override
+    {
+        auto nElements = (static_cast<std::uint8_t *>(context.end_ptr) -
+                          static_cast<std::uint8_t *>(context.base_ptr)) /
+                         context.type_size;
+        auto nIndexAccessed = (static_cast<std::uint8_t *>(context.access_ptr) -
+                               static_cast<std::uint8_t *>(context.base_ptr)) /
+                              context.type_size;
+
+        std::ostringstream oss;
+        oss << "Attempted to access index " << nIndexAccessed
+            << " in a vector of " << nElements
+            << " elements when evaluating VRT expression.",
+            throw std::runtime_error(oss.str());
+    }
+};
+
 class GDALExpressionEvaluator::Impl
 {
   public:
@@ -19,9 +40,15 @@ class GDALExpressionEvaluator::Impl
     std::vector<std::pair<std::string, double *>> m_aoVariables{};
     std::vector<std::pair<std::string, std::vector<double> *>> m_aoVectors{};
     std::vector<double> m_adfResults{};
+    vector_access_check m_oVectorAccessCheck{};
 
     bool m_bIsCompiled{false};
 
+    Impl()
+    {
+        m_oParser.register_vector_access_runtime_check(m_oVectorAccessCheck);
+    }
+
     CPLErr compile()
     {
         for (const auto &[osVariable, pdfValueLoc] : m_aoVariables)
@@ -107,7 +134,16 @@ CPLErr GDALExpressionEvaluator::Evaluate()
     }
 
     m_pImpl->m_adfResults.clear();
-    double value = m_pImpl->m_oExpression.value();  // force evaluation
+    double value;
+    try
+    {
+        value = m_pImpl->m_oExpression.value();  // force evaluation
+    }
+    catch (const std::exception &e)
+    {
+        CPLError(CE_Failure, CPLE_AppDefined, "%s", e.what());
+        return CE_Failure;
+    }
 
     const auto &results = m_pImpl->m_oExpression.results();