Protected against JsonValueWriter stack overflow

Add validation for the maximum JSON nesting depth in the JsonValueWriter.
This helps prevent a StackOverflowError that can potentially occur due
to excessive recursion when dealing with deeply nested JSON structures.

See gh-44627

Signed-off-by: Dmytro Nosan <[email protected]>

Author: nosan

spring-boot-project/spring-boot/src/main/java/org/springframework/boot/json/JsonValueWriter.java

@@ -47,8 +47,12 @@
  */
 class JsonValueWriter {
 
+	private static final int DEFAULT_MAX_NESTING_DEPTH = 1000;
+
 	private final Appendable out;
 
+	private final int maxNestingDepth;
+
 	private MemberPath path = MemberPath.ROOT;
 
 	private final Deque<JsonWriterFiltersAndProcessors> filtersAndProcessors = new ArrayDeque<>();
@@ -60,7 +64,18 @@ class JsonValueWriter {
 	 * @param out the {@link Appendable} used to receive the JSON output
 	 */
 	JsonValueWriter(Appendable out) {
+		this(out, DEFAULT_MAX_NESTING_DEPTH);
+	}
+
+	/**
+	 * Create a new {@link JsonValueWriter} instance.
+	 * @param out the {@link Appendable} used to receive the JSON output
+	 * @param maxNestingDepth the maximum allowed nesting depth for JSON objects and
+	 * arrays
+	 */
+	JsonValueWriter(Appendable out, int maxNestingDepth) {
 		this.out = out;
+		this.maxNestingDepth = maxNestingDepth;
 	}
 
 	void pushProcessors(JsonWriterFiltersAndProcessors jsonProcessors) {
@@ -145,6 +160,7 @@ private <V> boolean canWriteAsArray(Iterable<?> iterable) {
 	 */
 	void start(Series series) {
 		if (series != null) {
+			validateNestingDepth();
 			this.activeSeries.push(new ActiveSeries(series));
 			append(series.openChar);
 		}
@@ -272,6 +288,13 @@ private void writeString(Object value) {
 		}
 	}
 
+	private void validateNestingDepth() {
+		if (this.activeSeries.size() > this.maxNestingDepth) {
+			throw new IllegalStateException("JSON nesting depth (%s) exceeds maximum depth of %s (current path: %s)"
+				.formatted(this.activeSeries.size(), this.maxNestingDepth, this.path));
+		}
+	}
+
 	private void append(String value) {
 		try {
 			this.out.append(value);

spring-boot-project/spring-boot/src/test/java/org/springframework/boot/json/JsonValueWriterTests.java

@@ -18,6 +18,7 @@
 
 import java.io.File;
 import java.nio.file.Path;
+import java.util.ArrayList;
 import java.util.LinkedHashMap;
 import java.util.LinkedHashSet;
 import java.util.List;
@@ -253,6 +254,36 @@ void writeJavaNioPathShouldBeSerializedAsString() {
 			.isEqualTo(quoted("a\\%1$sb\\%1$sc".formatted(File.separator)));
 	}
 
+	@Test
+	void illegalStateExceptionShouldBeThrownWhenCollectionExceededNestingDepth() {
+		JsonValueWriter writer = new JsonValueWriter(new StringBuilder(), 128);
+		List<Object> list = new ArrayList<>();
+		list.add(list);
+		assertThatIllegalStateException().isThrownBy(() -> writer.write(list))
+			.withMessageStartingWith(
+					"JSON nesting depth (129) exceeds maximum depth of 128 (current path: [0][0][0][0][0][0][0][0][0][0][0][0]");
+	}
+
+	@Test
+	void illegalStateExceptionShouldBeThrownWhenMapExceededNestingDepth() {
+		JsonValueWriter writer = new JsonValueWriter(new StringBuilder(), 128);
+		Map<String, Object> map = new LinkedHashMap<>();
+		map.put("foo", Map.of("bar", map));
+		assertThatIllegalStateException().isThrownBy(() -> writer.write(map))
+			.withMessageStartingWith(
+					"JSON nesting depth (129) exceeds maximum depth of 128 (current path: foo.bar.foo.bar.foo.bar.foo");
+	}
+
+	@Test
+	void illegalStateExceptionShouldBeThrownWhenIterableExceededNestingDepth() {
+		JsonValueWriter writer = new JsonValueWriter(new StringBuilder(), 128);
+		List<Object> list = new ArrayList<>();
+		list.add(list);
+		assertThatIllegalStateException().isThrownBy(() -> writer.write((Iterable<Object>) list::iterator))
+			.withMessageStartingWith(
+					"JSON nesting depth (129) exceeds maximum depth of 128 (current path: [0][0][0][0][0][0][0][0][0][0][0][0]");
+	}
+
 	private <V> String write(V value) {
 		return doWrite((valueWriter) -> valueWriter.write(value));
 	}