Start work on #2195: add tentative API as PolymorphicTypeValidator

src/main/java/com/fasterxml/jackson/databind/jsontype/PolymorphicTypeValidator.java

@@ -0,0 +1,94 @@
+package com.fasterxml.jackson.databind.jsontype;
+
+import com.fasterxml.jackson.databind.*;
+import com.fasterxml.jackson.databind.cfg.MapperConfig;
+
+/**
+ * Interface for classes that handle validation of class name-based subtypes used
+ * with Polymorphic Deserialization: both via "default typing" and explicit
+ * {@code @JsonTypeInfo} when using class name as Type Identifier.
+ * The main purpose, initially, is to allow pluggable allow/deny lists to avoid
+ * security problems that occur with unlimited class names
+ * (See <a href="https://medium.com/@cowtowncoder/on-jackson-cves-dont-panic-here-is-what-you-need-to-know-54cd0d6e8062">
+ * this article</a> for full explanation).
+ *<p>
+ * Notes on implementations: implementations must be thread-safe and shareable (usually meaning they
+ * are stateless). Determinations for validity are usually effectively cached on per-property
+ * basis (by virtue of subtype deserializers being cached by polymorphic deserializers) so
+ * caching at validator level is usually not needed. If caching is used, however, it must be done
+ * in thread-safe manner as validators are shared within {@link ObjectMapper} as well as possible
+ * across mappers (in case of default/standard validator).
+ *
+ * @since 2.10
+ */
+public abstract class PolymorphicTypeValidator
+{
+    /**
+     * Definition of return values to indicate determination regarding validity.
+     */
+    public enum Validity {
+        /**
+         * Value that indicates that Class name or Class is allowed for use without further checking
+         */
+        ALLOWED,
+        /**
+         * Value that indicates that Class name or Class is NOT allowed and no further checks are
+         * needed or allowed
+         */
+        DENIED,
+
+        /**
+         * Value that indicates that Class name or Class validity can not be confirmed by validator
+         * and further checks are needed.
+         *<p>
+         * Typically if validator can not establish validity from Type Id or Class (name), eventual
+         * determination will be {@code DENIED}, for safety reasons.
+         */
+        INDETERMINATE
+        ;
+    }
+
+    /**
+     * Method called after intended class name for subtype has been read (and in case of minimal
+     * class name, expanded to fully-qualified class name) but before attempt is made to
+     * look up actual {@link java.lang.Class} or {@link JavaType}.
+     * Validator may be able to
+     * determine validity of eventual type (and return {@link Validity#ALLOWED} or
+     * {@link Validity#DENIED}) or, if not able to, can defer validation to actual
+     * resolved type by returning {@link Validity#INDETERMINATE}.
+     *<p>
+     * Validator may also choose to indicate denial by throwing a {@link JsonMappingException}
+     * (such as {@link com.fasterxml.jackson.databind.exc.InvalidTypeIdException})
+     *
+     * @param ctxt Context for resolution: typically will be {@code DeserializationContext}
+     * @param baseType Nominal base type used for polymorphic handling: subtypes MUST be instances
+     *   of this type and assignment compatibility is verified by Jackson core
+     * @param subClassName Name of class that will be resolved to {@link java.lang.Class} if
+     *   (and only if) validity check is not denied.
+     *
+     * @return Determination of validity of given class name, as a subtype of given base type:
+     *   should NOT return {@code null}
+     */
+    public abstract Validity validateSubClassName(MapperConfig<?> ctxt, JavaType baseType,
+            String subClassName) throws JsonMappingException;
+
+    /**
+     * Method called after class name has been resolved to actual type, in cases where previous
+     * call to {@link #validateSubClassName} returned {@link Validity#INDETERMINATE}.
+     * Validator should be able to determine validity and return appropriate {@link Validity}
+     * value, although it may also
+     *<p>
+     * Validator may also choose to indicate denial by throwing a {@link JsonMappingException}
+     * (such as {@link com.fasterxml.jackson.databind.exc.InvalidTypeIdException})
+     *
+     * @param ctxt Context for resolution: typically will be {@code DeserializationContext}
+     * @param baseType Nominal base type used for polymorphic handling: subtypes MUST be instances
+     *   of this type and assignment compatibility has been verified by Jackson core
+     * @param subType Resolved subtype to validate
+     *
+     * @return Determination of validity of given class name, as a subtype of given base type:
+     *   should NOT return {@code null}
+     */
+    public abstract Validity validateSubType(MapperConfig<?> ctxt, JavaType baseType,
+            JavaType subType) throws JsonMappingException;
+}

src/main/java/com/fasterxml/jackson/databind/jsontype/impl/TypeDeserializerBase.java

@@ -133,8 +133,8 @@ public String toString()
         sb.append('[').append(getClass().getName());
         sb.append("; base-type:").append(_baseType);
         sb.append("; id-resolver: ").append(_idResolver);
-    	    sb.append(']');
-    	    return sb.toString();
+        sb.append(']');
+        return sb.toString();
     }
 
     /*
@@ -242,14 +242,13 @@ protected Object _deserializeWithNativeTypeId(JsonParser jp, DeserializationCont
      * 
      * @since 2.4
      */
-    protected Object _deserializeWithNativeTypeId(JsonParser jp, DeserializationContext ctxt, Object typeId)
+    protected Object _deserializeWithNativeTypeId(JsonParser p, DeserializationContext ctxt, Object typeId)
         throws IOException
     {
         JsonDeserializer<Object> deser;
         if (typeId == null) {
-            /* 04-May-2014, tatu: Should error be obligatory, or should there be another method
-             *   for "try to deserialize with native tpye id"?
-             */
+            // 04-May-2014, tatu: Should error be obligatory, or should there be another method
+            //   for "try to deserialize with native type id"?
             deser = _findDefaultImplDeserializer(ctxt);
             if (deser == null) {
                 return ctxt.reportInputMismatch(baseType(),
@@ -259,7 +258,7 @@ protected Object _deserializeWithNativeTypeId(JsonParser jp, DeserializationCont
             String typeIdStr = (typeId instanceof String) ? (String) typeId : String.valueOf(typeId);
             deser = _findDeserializer(ctxt, typeIdStr);
         }
-        return deser.deserialize(jp, ctxt);
+        return deser.deserialize(p, ctxt);
     }
 
     /**

src/main/java/com/fasterxml/jackson/databind/jsontype/impl/TypeNameIdResolver.java

@@ -113,9 +113,8 @@ protected String idFromClass(Class<?> clazz)
 
     @Override
     public String idFromValueAndType(Object value, Class<?> type) {
-        /* 18-Jan-2013, tatu: We may be called with null value occasionally
-         *   it seems; nothing much we can figure out that way.
-         */
+        // 18-Jan-2013, tatu: We may be called with null value occasionally
+        //   it seems; nothing much we can figure out that way.
         if (value == null) {
             return idFromClass(type);
         }
@@ -128,11 +127,10 @@ public JavaType typeFromId(DatabindContext context, String id) {
     }
 
     protected JavaType _typeFromId(String id) {
-        /* Now: if no type is found, should we try to locate it by
-         * some other means? (specifically, if in same package as base type,
-         * could just try Class.forName)
-         * For now let's not add any such workarounds; can add if need be
-         */
+        // Now: if no type is found, should we try to locate it by
+        // some other means? (specifically, if in same package as base type,
+        // could just try Class.forName)
+        // For now let's not add any such workarounds; can add if need be
         return _idToType.get(id);
     }