Account for all array objects when checking array size in SpEL

Prior to this commit, ConstructorReference.createArray() enforced the
MAX_ARRAY_ELEMENTS threshold for multi-dimensional arrays by checking
only the product of all dimension sizes, which is equivalent to the
total number of leaf-level elements. However, Array.newInstance()
allocates a distinct array object at every nesting level, not just at
the leaf level. For dimensions [d0, d1, ..., dk-1], the total number
of array objects created is 1 + d0 + d0*d1 + ... + d0*d1*...*d(k-2).
As a result, an expression such as new int[262143][1][1]...[1], whose
trailing dimensions are all 1, kept the leaf-element product just
under the threshold while still causing tens of millions of array
objects to be allocated.

To address that, this commit introduces a second running total,
totalArrayObjects, alongside the existing leaf-element product in the
multi-dimensional array construction loop. Both totals are checked
against MAX_ARRAY_ELEMENTS on every iteration, so array constructions
that fan out into an excessive number of array objects are now
rejected even when the leaf-element count remains within bounds.

Note that SimpleEvaluationContext does not permit array construction
in SpEL expressions at all, so this fix effectively only changes
behavior for expressions evaluated via StandardEvaluationContext.

Tests have been added to ArrayConstructorTests to verify that the new
check rejects array constructions with an excessive number of array
objects and that array constructions just under the threshold remain
unaffected.

Closes gh-36998

Author: sbrannen

spring-expression/src/main/java/org/springframework/expression/spel/ast/ConstructorReference.java

@@ -67,7 +67,9 @@ public class ConstructorReference extends SpelNodeImpl {
 
 	/**
 	 * Maximum number of elements permitted in an array declaration, applying
-	 * to one-dimensional as well as multi-dimensional arrays.
+	 * to one-dimensional as well as multi-dimensional arrays. For the latter,
+	 * this also bounds the total number of array objects allocated across all
+	 * nesting levels, not just the product of the dimension sizes.
 	 * @since 5.3.17
 	 */
 	private static final int MAX_ARRAY_ELEMENTS = 256 * 1024; // 256K
@@ -312,12 +314,18 @@ private TypedValue createArray(ExpressionState state) throws EvaluationException
 					// Multidimensional - hold onto your hat!
 					int[] dims = new int[this.dimensions.length];
 					long numElements = 1;
+					// Java allocates a distinct array object at every nesting level, so we
+					// also have to cap the total number of array objects created, not just
+					// the product of all dimension sizes (the number of leaf elements).
+					long totalArrayObjects = 0;
 					for (int d = 0; d < this.dimensions.length; d++) {
 						TypedValue o = this.dimensions[d].getTypedValue(state);
 						int arraySize = ExpressionUtils.toInt(typeConverter, o);
 						dims[d] = arraySize;
+						totalArrayObjects += numElements;
 						numElements *= arraySize;
 						checkNumElements(numElements);
+						checkNumElements(totalArrayObjects);
 					}
 					newArray = Array.newInstance(componentType, dims);
 				}

spring-expression/src/test/java/org/springframework/expression/spel/ArrayConstructorTests.java

@@ -95,6 +95,12 @@ void errorCases() {
 		int threshold = 256 * 1024; // ConstructorReference.MAX_ARRAY_ELEMENTS
 		evaluateAndCheckError("new int[T(java.lang.Integer).MAX_VALUE]", SpelMessage.MAX_ARRAY_ELEMENTS_THRESHOLD_EXCEEDED, 0, threshold);
 		evaluateAndCheckError("new int[1024 * 1024][1024 * 1024]", SpelMessage.MAX_ARRAY_ELEMENTS_THRESHOLD_EXCEEDED, 0, threshold);
+		// The product of all dimension sizes stays just under the threshold, but Java
+		// allocates an array object at every nesting level, so the total number of
+		// array objects created (1 root + 262143 sub-arrays) meets the threshold.
+		evaluateAndCheckError("new int[262143][1]", SpelMessage.MAX_ARRAY_ELEMENTS_THRESHOLD_EXCEEDED, 0, threshold);
+		evaluateAndCheckError("new int[262143][1][1][1][1][1][1][1][1][1][1]",
+				SpelMessage.MAX_ARRAY_ELEMENTS_THRESHOLD_EXCEEDED, 0, threshold);
 	}
 
 	@Test
@@ -116,6 +122,9 @@ void multiDimensionalArrays() {
 		evaluate("new String[3][2][1]",
 				"[[Ljava.lang.String;[3]{[2]{[1]{null},[1]{null}},[2]{[1]{null},[1]{null}},[2]{[1]{null},[1]{null}}}",
 				String[][][].class);
+		// 1 root array + 262142 sub-arrays = 262143 array objects, just under the
+		// MAX_ARRAY_ELEMENTS threshold, so this must not be rejected.
+		evaluate("new int[262142][1].length", 262142, Integer.class);
 	}
 
 	@Test