fastjson反序列化漏洞流程分析

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// pom.xml

<?xml version="1.0" encoding="UTF-8"?>
<project xmlns="http://maven.apache.org/POM/4.0.0"
         xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance"
         xsi:schemaLocation="http://maven.apache.org/POM/4.0.0 http://maven.apache.org/xsd/maven-4.0.0.xsd">
    <modelVersion>4.0.0</modelVersion>

    <groupId>org.example</groupId>
    <artifactId>fastjson</artifactId>
    <version>1.0-SNAPSHOT</version>

    <dependencies>
        <dependency>
            <groupId>com.alibaba</groupId>
            <artifactId>fastjson</artifactId>
            <version>1.2.24</version>
        </dependency>
    </dependencies>

    <properties>
        <maven.compiler.source>21</maven.compiler.source>
        <maven.compiler.target>21</maven.compiler.target>
        <project.build.sourceEncoding>UTF-8</project.build.sourceEncoding>
    </properties>

</project>

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package org.example;

import java.util.Map;

public class Person {
    private String name;
    private int age;
    private Map map;

    public Person() {
        System.out.println("constructor");
    }

    public String getName() {
        System.out.println("getName");
        return name;
    }

    public void setName(String name) {
        System.out.println("setName");
        this.name = name;
    }

    public int getAge() {
        System.out.println("getAge");
        return age;
    }

    public void setAge(int age) {
        System.out.println("setAge");
        this.age = age;
    }

    public Map getMap() {
        System.out.println("getMap");
        return map;
    }
}

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package org.example;

import com.alibaba.fastjson.JSON;
import com.alibaba.fastjson.JSONObject;

public class JSONUnser {
    public static void main(String[] args) throws Exception {
//        String s = "{\"param1\":\"aaa\",\"param2\":\"bbb\"}"; 
//        String s = "{\"age\":\"18\",\"name\":\"abc\"}";
        String s = "{\"@type\":\"org.example.Person\",\"age\":\"18\",\"name\":\"ttt\"}";
//        String s = "{\"@type\":\"org.example.Test\", \"cmd\":\"calc\"}";


        JSONObject jsonObject = JSON.parseObject(s);
//         Person person = JSON.parseObject(jsonObject);
         System.out.println(jsonObject);
    }
}

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// DefaultJSONParser.java

public final Object parseObject(final Map object, Object fieldName) {
        final JSONLexer lexer = this.lexer;
        
        if (lexer.token() == JSONToken.NULL) {
            lexer.nextToken();
            return null;
        }
        
        if (lexer.token() == JSONToken.RBRACE) {
            lexer.nextToken();
            return object;
        }

        if (lexer.token() != JSONToken.LBRACE && lexer.token() != JSONToken.COMMA) {
            throw new JSONException("syntax error, expect {, actual " + lexer.tokenName() + ", " + lexer.info());
        }

       ParseContext context = this.context;
        try {
            boolean setContextFlag = false;
            for (;;) {
                lexer.skipWhitespace();
                char ch = lexer.getCurrent();
                if (lexer.isEnabled(Feature.AllowArbitraryCommas)) {
                    while (ch == ',') {
                        lexer.next();
                        lexer.skipWhitespace();
                        ch = lexer.getCurrent();
                    }
                }

                boolean isObjectKey = false;
                Object key; // 
                if (ch == '"') {
                    key = lexer.scanSymbol(symbolTable, '"');
                    lexer.skipWhitespace();
                    ch = lexer.getCurrent();
                    if (ch != ':') {
                        throw new JSONException("expect ':' at " + lexer.pos() + ", name " + key);
                    }
                } else if (ch == '}') {
                    lexer.next();
                    lexer.resetStringPosition();
                    lexer.nextToken();

                    if (!setContextFlag) {
                        if (this.context != null && fieldName == this.context.fieldName && object == this.context.object) {
                            context = this.context;
                        } else {
                            ParseContext contextR = setContext(object, fieldName);
                            if (context == null) {
                                context = contextR;
                            }
                            setContextFlag = true;
                        }
                    }

                    return object;
                } else if (ch == '\'') {
                    if (!lexer.isEnabled(Feature.AllowSingleQuotes)) {
                        throw new JSONException("syntax error");
                    }

                    key = lexer.scanSymbol(symbolTable, '\'');
                    lexer.skipWhitespace();
                    ch = lexer.getCurrent();
                    if (ch != ':') {
                        throw new JSONException("expect ':' at " + lexer.pos());
                    }
                } else if (ch == EOI) {
                    throw new JSONException("syntax error");
                } else if (ch == ',') {
                    throw new JSONException("syntax error");
                } else if ((ch >= '0' && ch <= '9') || ch == '-') {
                    lexer.resetStringPosition();
                    lexer.scanNumber();
                    try {
                    if (lexer.token() == JSONToken.LITERAL_INT) {
                        key = lexer.integerValue();
                    } else {
                        key = lexer.decimalValue(true);
                    }
                    } catch (NumberFormatException e) {
                        throw new JSONException("parse number key error" + lexer.info());
                    }
                    ch = lexer.getCurrent();
                    if (ch != ':') {
                        throw new JSONException("parse number key error" + lexer.info());
                    }
                } else if (ch == '{' || ch == '[') {
                    lexer.nextToken();
                    key = parse();
                    isObjectKey = true;
                } else {
                    if (!lexer.isEnabled(Feature.AllowUnQuotedFieldNames)) {
                        throw new JSONException("syntax error");
                    }

                    key = lexer.scanSymbolUnQuoted(symbolTable);
                    lexer.skipWhitespace();
                    ch = lexer.getCurrent();
                    if (ch != ':') {
                        throw new JSONException("expect ':' at " + lexer.pos() + ", actual " + ch);
                    }
                }

                if (!isObjectKey) {
                    lexer.next();
                    lexer.skipWhitespace();
                }

                ch = lexer.getCurrent();

                lexer.resetStringPosition();

                if (key == JSON.DEFAULT_TYPE_KEY && !lexer.isEnabled(Feature.DisableSpecialKeyDetect)) {
                    String typeName = lexer.scanSymbol(symbolTable, '"');
                    Class<?> clazz = TypeUtils.loadClass(typeName, config.getDefaultClassLoader()); //

                    if (clazz == null) {
                        object.put(JSON.DEFAULT_TYPE_KEY, typeName);
                        continue;
                    }

                    lexer.nextToken(JSONToken.COMMA);
                    if (lexer.token() == JSONToken.RBRACE) {
                        lexer.nextToken(JSONToken.COMMA);
                        try {
                            Object instance = null;
                            ObjectDeserializer deserializer = this.config.getDeserializer(clazz);
                            if (deserializer instanceof JavaBeanDeserializer) {
                                instance = ((JavaBeanDeserializer) deserializer).createInstance(this, clazz);
                            }

                            if (instance == null) {
                                if (clazz == Cloneable.class) {
                                    instance = new HashMap();
                                } else if ("java.util.Collections$EmptyMap".equals(typeName)) {
                                    instance = Collections.emptyMap();
                                } else {
                                    instance = clazz.newInstance();
                                }
                            }

                            return instance;
                        } catch (Exception e) {
                            throw new JSONException("create instance error", e);
                        }
                    }
                    
                    this.setResolveStatus(TypeNameRedirect);

                    if (this.context != null && !(fieldName instanceof Integer)) {
                        this.popContext();
                    }
                    
                    if (object.size() > 0) {
                        Object newObj = TypeUtils.cast(object, clazz, this.config);
                        this.parseObject(newObj);
                        return newObj;
                    }

                    ObjectDeserializer deserializer = config.getDeserializer(clazz);
                    return deserializer.deserialze(this, clazz, fieldName);
                }

                if (key == "$ref" && !lexer.isEnabled(Feature.DisableSpecialKeyDetect)) {
                    lexer.nextToken(JSONToken.LITERAL_STRING);
                    if (lexer.token() == JSONToken.LITERAL_STRING) {
                        String ref = lexer.stringVal();
                        lexer.nextToken(JSONToken.RBRACE);

                        Object refValue = null;
                        if ("@".equals(ref)) {
                            if (this.context != null) {
                                ParseContext thisContext = this.context;
                                Object thisObj = thisContext.object;
                                if (thisObj instanceof Object[] || thisObj instanceof Collection<?>) {
                                    refValue = thisObj;
                                } else if (thisContext.parent != null) {
                                    refValue = thisContext.parent.object;
                                }
                            }
                        } else if ("..".equals(ref)) {
                            if (context.object != null) {
                                refValue = context.object;
                            } else {
                                addResolveTask(new ResolveTask(context, ref));
                                setResolveStatus(DefaultJSONParser.NeedToResolve);
                            }
                        } else if ("$".equals(ref)) {
                            ParseContext rootContext = context;
                            while (rootContext.parent != null) {
                                rootContext = rootContext.parent;
                            }

                            if (rootContext.object != null) {
                                refValue = rootContext.object;
                            } else {
                                addResolveTask(new ResolveTask(rootContext, ref));
                                setResolveStatus(DefaultJSONParser.NeedToResolve);
                            }
                        } else {
                            addResolveTask(new ResolveTask(context, ref));
                            setResolveStatus(DefaultJSONParser.NeedToResolve);
                        }

                        if (lexer.token() != JSONToken.RBRACE) {
                            throw new JSONException("syntax error");
                        }
                        lexer.nextToken(JSONToken.COMMA);

                        return refValue;
                    } else {
                        throw new JSONException("illegal ref, " + JSONToken.name(lexer.token()));
                    }
                }

                if (!setContextFlag) {
                    if (this.context != null && fieldName == this.context.fieldName && object == this.context.object) {
                        context = this.context;
                    } else {
                        ParseContext contextR = setContext(object, fieldName);
                        if (context == null) {
                            context = contextR;
                        }
                        setContextFlag = true;
                    }
                }

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    public static JavaBeanInfo build(Class<?> clazz, Type type, PropertyNamingStrategy propertyNamingStrategy) {
        JSONType jsonType = clazz.getAnnotation(JSONType.class);

        Class<?> builderClass = getBuilderClass(jsonType);

        Field[] declaredFields = clazz.getDeclaredFields();
        Method[] methods = clazz.getMethods();

        Constructor<?> defaultConstructor = getDefaultConstructor(builderClass == null ? clazz : builderClass);
        Constructor<?> creatorConstructor = null;
        Method buildMethod = null;

        List<FieldInfo> fieldList = new ArrayList<FieldInfo>();

        if (defaultConstructor == null && !(clazz.isInterface() || Modifier.isAbstract(clazz.getModifiers()))) {
            creatorConstructor = getCreatorConstructor(clazz);
            if (creatorConstructor != null) { // 基于标记 JSONCreator 注解的构造方法
                TypeUtils.setAccessible(creatorConstructor);

                Class<?>[] types = creatorConstructor.getParameterTypes();
                if (types.length > 0) {
                    Annotation[][] paramAnnotationArrays = creatorConstructor.getParameterAnnotations();
                    for (int i = 0; i < types.length; ++i) {
                        Annotation[] paramAnnotations = paramAnnotationArrays[i];
                        JSONField fieldAnnotation = null;
                        for (Annotation paramAnnotation : paramAnnotations) {
                            if (paramAnnotation instanceof JSONField) {
                                fieldAnnotation = (JSONField) paramAnnotation;
                                break;
                            }
                        }
                        if (fieldAnnotation == null) {
                            throw new JSONException("illegal json creator");
                        }
                        Class<?> fieldClass = types[i];
                        Type fieldType = creatorConstructor.getGenericParameterTypes()[i];
                        Field field = TypeUtils.getField(clazz, fieldAnnotation.name(), declaredFields);
                        final int ordinal = fieldAnnotation.ordinal();
                        final int serialzeFeatures = SerializerFeature.of(fieldAnnotation.serialzeFeatures());
                        final int parserFeatures = Feature.of(fieldAnnotation.parseFeatures());
                        FieldInfo fieldInfo = new FieldInfo(fieldAnnotation.name(), clazz, fieldClass, fieldType, field,
                                                            ordinal, serialzeFeatures, parserFeatures);
                        add(fieldList, fieldInfo);
                    }
                }

                return new JavaBeanInfo(clazz, builderClass, null, creatorConstructor, null, null, jsonType, fieldList);
            }

            Method factoryMethod = getFactoryMethod(clazz, methods); // 基于标记 JSONCreator 注解的工厂方法
            if (factoryMethod != null) {
                TypeUtils.setAccessible(factoryMethod);

                Class<?>[] types = factoryMethod.getParameterTypes();
                if (types.length > 0) {
                    Annotation[][] paramAnnotationArrays = factoryMethod.getParameterAnnotations();
                    for (int i = 0; i < types.length; ++i) {
                        Annotation[] paramAnnotations = paramAnnotationArrays[i];
                        JSONField fieldAnnotation = null;
                        for (Annotation paramAnnotation : paramAnnotations) {
                            if (paramAnnotation instanceof JSONField) {
                                fieldAnnotation = (JSONField) paramAnnotation;
                                break;
                            }
                        }
                        if (fieldAnnotation == null) {
                            throw new JSONException("illegal json creator");
                        }

                        Class<?> fieldClass = types[i];
                        Type fieldType = factoryMethod.getGenericParameterTypes()[i];
                        Field field = TypeUtils.getField(clazz, fieldAnnotation.name(), declaredFields);
                        final int ordinal = fieldAnnotation.ordinal();
                        final int serialzeFeatures = SerializerFeature.of(fieldAnnotation.serialzeFeatures());
                        final int parserFeatures = Feature.of(fieldAnnotation.parseFeatures());
                        FieldInfo fieldInfo = new FieldInfo(fieldAnnotation.name(), clazz, fieldClass, fieldType, field,
                                                            ordinal, serialzeFeatures, parserFeatures);
                        add(fieldList, fieldInfo);
                    }
                }

                return new JavaBeanInfo(clazz, builderClass, null, null, factoryMethod, null, jsonType, fieldList);
            }

            throw new JSONException("default constructor not found. " + clazz);
        }

        if (defaultConstructor != null) {
            TypeUtils.setAccessible(defaultConstructor);
        }

        if (builderClass != null) {
            String withPrefix = null;

            JSONPOJOBuilder builderAnno = builderClass.getAnnotation(JSONPOJOBuilder.class);
            if (builderAnno != null) {
                withPrefix = builderAnno.withPrefix();
            }

            if (withPrefix == null || withPrefix.length() == 0) {
                withPrefix = "with";
            }

            for (Method method : builderClass.getMethods()) {
                if (Modifier.isStatic(method.getModifiers())) {
                    continue;
                }

                if (!(method.getReturnType().equals(builderClass))) {
                    continue;
                }

                int ordinal = 0, serialzeFeatures = 0, parserFeatures = 0;

                JSONField annotation = method.getAnnotation(JSONField.class);

                if (annotation == null) {
                    annotation = TypeUtils.getSuperMethodAnnotation(clazz, method);
                }

                if (annotation != null) {
                    if (!annotation.deserialize()) {
                        continue;
                    }

                    ordinal = annotation.ordinal();
                    serialzeFeatures = SerializerFeature.of(annotation.serialzeFeatures());
                    parserFeatures = Feature.of(annotation.parseFeatures());

                    if (annotation.name().length() != 0) {
                        String propertyName = annotation.name();
                        add(fieldList, new FieldInfo(propertyName, method, null, clazz, type, ordinal, serialzeFeatures, parserFeatures, 
                                                     annotation, null, null));
                        continue;
                    }
                }

                String methodName = method.getName();
                if (!methodName.startsWith(withPrefix)) {
                    continue;
                }

                if (methodName.length() <= withPrefix.length()) {
                    continue;
                }

                char c0 = methodName.charAt(withPrefix.length());

                if (!Character.isUpperCase(c0)) {
                    continue;
                }

                StringBuilder properNameBuilder = new StringBuilder(methodName.substring(withPrefix.length()));
                properNameBuilder.setCharAt(0, Character.toLowerCase(c0));

                String propertyName = properNameBuilder.toString();
                
                add(fieldList, new FieldInfo(propertyName, method, null, clazz, type, ordinal, serialzeFeatures, parserFeatures, 
                                             annotation, null, null));
            }

            if (builderClass != null) {
                JSONPOJOBuilder builderAnnotation = builderClass.getAnnotation(JSONPOJOBuilder.class);

                String buildMethodName = null;
                if (builderAnnotation != null) {
                    buildMethodName = builderAnnotation.buildMethod();
                }

                if (buildMethodName == null || buildMethodName.length() == 0) {
                    buildMethodName = "build";
                }

                try {
                    buildMethod = builderClass.getMethod(buildMethodName);
                } catch (NoSuchMethodException e) {
                    // skip
                } catch (SecurityException e) {
                    // skip
                }

                if (buildMethod == null) {
                    try {
                        buildMethod = builderClass.getMethod("create");
                    } catch (NoSuchMethodException e) {
                        // skip
                    } catch (SecurityException e) {
                        // skip
                    }
                }

                if (buildMethod == null) {
                    throw new JSONException("buildMethod not found.");
                }

                TypeUtils.setAccessible(buildMethod);
            }
        }

        for (Method method : methods) { //
            int ordinal = 0, serialzeFeatures = 0, parserFeatures = 0;
            String methodName = method.getName();
            if (methodName.length() < 4) {
                continue;
            }

            if (Modifier.isStatic(method.getModifiers())) {
                continue;
            }

            // support builder set
            if (!(method.getReturnType().equals(Void.TYPE) || method.getReturnType().equals(method.getDeclaringClass()))) {
                continue;
            }
            Class<?>[] types = method.getParameterTypes();
            if (types.length != 1) {
                continue;
            }

            JSONField annotation = method.getAnnotation(JSONField.class);

            if (annotation == null) {
                annotation = TypeUtils.getSuperMethodAnnotation(clazz, method);
            }

            if (annotation != null) {
                if (!annotation.deserialize()) {
                    continue;
                }

                ordinal = annotation.ordinal();
                serialzeFeatures = SerializerFeature.of(annotation.serialzeFeatures());
                parserFeatures = Feature.of(annotation.parseFeatures());

                if (annotation.name().length() != 0) {
                    String propertyName = annotation.name();
                    add(fieldList, new FieldInfo(propertyName, method, null, clazz, type, ordinal, serialzeFeatures, parserFeatures, 
                                                 annotation, null, null));
                    continue;
                }
            }

            if (!methodName.startsWith("set")) { // TODO "set"的判断放在 JSONField 注解后面，意思是允许非 setter 方法标记 JSONField 注解？
                continue;
            }

            char c3 = methodName.charAt(3);

            String propertyName;
            if (Character.isUpperCase(c3) //
                || c3 > 512 // for unicode method name
            ) {
                if (TypeUtils.compatibleWithJavaBean) {
                    propertyName = TypeUtils.decapitalize(methodName.substring(3));
                } else {
                    propertyName = Character.toLowerCase(methodName.charAt(3)) + methodName.substring(4);
                }
            } else if (c3 == '_') {
                propertyName = methodName.substring(4);
            } else if (c3 == 'f') {
                propertyName = methodName.substring(3);
            } else if (methodName.length() >= 5 && Character.isUpperCase(methodName.charAt(4))) {
                propertyName = TypeUtils.decapitalize(methodName.substring(3));
            } else {
                continue;
            }

            Field field = TypeUtils.getField(clazz, propertyName, declaredFields);
            if (field == null && types[0] == boolean.class) {
                String isFieldName = "is" + Character.toUpperCase(propertyName.charAt(0)) + propertyName.substring(1);
                field = TypeUtils.getField(clazz, isFieldName, declaredFields);
            }

            JSONField fieldAnnotation = null;
            if (field != null) {
                fieldAnnotation = field.getAnnotation(JSONField.class);

                if (fieldAnnotation != null) {
                    if (!fieldAnnotation.deserialize()) {
                        continue;
                    }
                    
                    ordinal = fieldAnnotation.ordinal();
                    serialzeFeatures = SerializerFeature.of(fieldAnnotation.serialzeFeatures());
                    parserFeatures = Feature.of(fieldAnnotation.parseFeatures());

                    if (fieldAnnotation.name().length() != 0) {
                        propertyName = fieldAnnotation.name();
                        add(fieldList, new FieldInfo(propertyName, method, field, clazz, type, ordinal,
                                                     serialzeFeatures, parserFeatures, annotation, fieldAnnotation, null));
                        continue;
                    }
                }

            }
            
            if (propertyNamingStrategy != null) {
                propertyName = propertyNamingStrategy.translate(propertyName);
            }

            add(fieldList, new FieldInfo(propertyName, method, field, clazz, type, ordinal, serialzeFeatures, parserFeatures,
                                         annotation, fieldAnnotation, null));
        }

        for (Field field : clazz.getFields()) { // public static fields
            int modifiers = field.getModifiers();
            if ((modifiers & Modifier.STATIC) != 0) {
                continue;
            }
            
            if((modifiers & Modifier.FINAL) != 0) {
                Class<?> fieldType = field.getType();
                boolean supportReadOnly = Map.class.isAssignableFrom(fieldType) 
                        || Collection.class.isAssignableFrom(fieldType)
                        || AtomicLong.class.equals(fieldType) //
                        || AtomicInteger.class.equals(fieldType) //
                        || AtomicBoolean.class.equals(fieldType);
                if (!supportReadOnly) {
                    continue;
                }
            }

            boolean contains = false;
            for (FieldInfo item : fieldList) {
                if (item.name.equals(field.getName())) {
                    contains = true;
                    break; // 已经是 contains = true，无需继续遍历
                }
            }

            if (contains) {
                continue;
            }

            int ordinal = 0, serialzeFeatures = 0, parserFeatures = 0;
            String propertyName = field.getName();

            JSONField fieldAnnotation = field.getAnnotation(JSONField.class);

            if (fieldAnnotation != null) {
                if (!fieldAnnotation.deserialize()) {
                    continue;
                }
                
                ordinal = fieldAnnotation.ordinal();
                serialzeFeatures = SerializerFeature.of(fieldAnnotation.serialzeFeatures());
                parserFeatures = Feature.of(fieldAnnotation.parseFeatures());

                if (fieldAnnotation.name().length() != 0) {
                    propertyName = fieldAnnotation.name();
                }
            }
            
            if (propertyNamingStrategy != null) {
                propertyName = propertyNamingStrategy.translate(propertyName);
            }
            
            add(fieldList, new FieldInfo(propertyName, null, field, clazz, type, ordinal, serialzeFeatures, parserFeatures, null,
                                         fieldAnnotation, null));
        }

        for (Method method : clazz.getMethods()) { // getter methods
            String methodName = method.getName();
            if (methodName.length() < 4) {
                continue;
            }

            if (Modifier.isStatic(method.getModifiers())) {
                continue;
            }

            if (methodName.startsWith("get") && Character.isUpperCase(methodName.charAt(3))) {
                if (method.getParameterTypes().length != 0) {
                    continue;
                }

                if (Collection.class.isAssignableFrom(method.getReturnType()) //
                    || Map.class.isAssignableFrom(method.getReturnType()) //
                    || AtomicBoolean.class == method.getReturnType() //
                    || AtomicInteger.class == method.getReturnType() //
                    || AtomicLong.class == method.getReturnType() //
                ) {
                    String propertyName;

                    JSONField annotation = method.getAnnotation(JSONField.class);
                    if (annotation != null && annotation.deserialize()) {
                        continue;
                    }
                    
                    if (annotation != null && annotation.name().length() > 0) {
                        propertyName = annotation.name();
                    } else {
                        propertyName = Character.toLowerCase(methodName.charAt(3)) + methodName.substring(4);
                    }
                    
                    FieldInfo fieldInfo = getField(fieldList, propertyName);
                    if (fieldInfo != null) {
                        continue;
                    }

                    if (propertyNamingStrategy != null) {
                        propertyName = propertyNamingStrategy.translate(propertyName);
                    }
                    
                    add(fieldList, new FieldInfo(propertyName, method, null, clazz, type, 0, 0, 0, annotation, null, null));
                }
            }
        }

        return new JavaBeanInfo(clazz, builderClass, defaultConstructor, null, null, buildMethod, jsonType, fieldList);
    }