[2.8.x] add depth limit for JSON form binding

core/play/src/main/scala/play/api/data/Form.scala

@@ -89,7 +89,7 @@ case class Form[T](mapping: Mapping[T], data: Map[String, String], errors: Seq[F
     logger.warn(
       s"Binding json field from form with a hardcoded max size of ${Form.FromJsonMaxChars} bytes. This is deprecated. Use bind(JsValue, Int) instead."
     )
-    bind(FormUtils.fromJson(data, Form.FromJsonMaxChars))
+    bind(FormUtils.fromJson(data, Form.FromJsonMaxChars, Form.FromJsonMaxDepth))
   }
 
   /**
@@ -100,7 +100,18 @@ case class Form[T](mapping: Mapping[T], data: Map[String, String], errors: Seq[F
    *                 of the JSON. `parse.DefaultMaxTextLength` is recommended to passed for this parameter.
    * @return a copy of this form, filled with the new data
    */
-  def bind(data: JsValue, maxChars: Long): Form[T] = bind(FormUtils.fromJson(data, maxChars))
+  def bind(data: JsValue, maxChars: Long): Form[T] = bind(FormUtils.fromJson(data, maxChars, Form.FromJsonMaxDepth))
+
+  /**
+   * Binds data to this form, i.e. handles form submission.
+   *
+   * @param data Json data to submit
+   * @param maxChars The maximum number of chars allowed to be used in the intermediate map representation
+   *                 of the JSON. `parse.DefaultMaxTextLength` is recommended to passed for this parameter.
+   * @param maxDepth The maximum level of nesting for JSON objects and arrays.
+   * @return a copy of this form, filled with the new data
+   */
+  def bind(data: JsValue, maxChars: Long, maxDepth: Int): Form[T] = bind(FormUtils.fromJson(data, maxChars, maxDepth))
 
   /**
    * Binds request data to this form, i.e. handles form submission.
@@ -358,7 +369,15 @@ object Form {
    * JSON. Defaults to 100k which is the default of parser.maxMemoryBuffer
    */
   @InternalApi
-  val FromJsonMaxChars: Long = 102400
+  final val FromJsonMaxChars: Long = 102400
+
+  /**
+   * INTERNAL API
+   *
+   * Default maximum depth of objects and arrays supported in JSON forms
+   */
+  @InternalApi
+  final val FromJsonMaxDepth: Int = 64
 
   /**
    * Creates a new form from a mapping.
@@ -408,54 +427,87 @@ object Form {
 }
 
 private[data] object FormUtils {
-  def fromJson(js: JsValue, maxChars: Long): Map[String, String] = doFromJson(FromJsonRoot(js), Map.empty, 0, maxChars)
+  @deprecated("Use fromJson with maxDepth parameter", "2.8.16")
+  def fromJson(js: JsValue, maxChars: Long): Map[String, String] =
+    doFromJson(FromJsonRoot(js), Map.empty, 0, maxChars, Form.FromJsonMaxDepth)
+
+  def fromJson(js: JsValue, maxChars: Long, maxDepth: Int): Map[String, String] =
+    doFromJson(FromJsonRoot(js), Map.empty, 0, maxChars, maxDepth)
 
   @annotation.tailrec
   private def doFromJson(
       context: FromJsonContext,
       form: Map[String, String],
       cumulativeChars: Int,
-      maxChars: Long
-  ): Map[String, String] = context match {
-    case FromJsonTerm              => form
-    case ctx: FromJsonContextValue =>
-      // Ensure this contexts next is initialised, this prevents unbounded recursion.
-      ctx.next
-      ctx.value match {
-        case obj: JsObject if obj.fields.nonEmpty =>
-          doFromJson(FromJsonObject(ctx, obj.fields.toIndexedSeq, 0), form, cumulativeChars, maxChars)
-        case JsArray(values) if values.nonEmpty =>
-          doFromJson(FromJsonArray(ctx, values, 0), form, cumulativeChars, maxChars)
-        case JsNull | JsArray(_) | JsObject(_) =>
-          doFromJson(ctx.next, form, cumulativeChars, maxChars)
-        case simple =>
-          val value = simple match {
-            case JsString(v)  => v
-            case JsNumber(v)  => v.toString
-            case JsBoolean(v) => v.toString
-          }
-          val prefix             = ctx.prefix
-          val newCumulativeChars = cumulativeChars + prefix.length + value.length
-          if (newCumulativeChars > maxChars) {
-            throw FormJsonExpansionTooLarge(maxChars)
-          }
-          doFromJson(ctx.next, form.updated(prefix, value), newCumulativeChars, maxChars)
-      }
+      maxChars: Long,
+      maxDepth: Int,
+  ): Map[String, String] = {
+    if (cumulativeChars > maxChars)
+      throw FormJsonExpansionTooLarge(maxChars)
+    if (context.depth > maxDepth)
+      throw FormJsonExpansionTooDeep(maxDepth)
+    context match {
+      case FromJsonTerm              => form
+      case ctx: FromJsonContextValue =>
+        // Ensure this contexts next is initialised, this prevents unbounded recursion.
+        ctx.next
+        ctx.value match {
+          case obj: JsObject if obj.fields.nonEmpty =>
+            doFromJson(
+              FromJsonObject(ctx, obj.fields.toIndexedSeq, 0),
+              form,
+              cumulativeChars,
+              maxChars,
+              maxDepth
+            )
+          case JsArray(values) if values.nonEmpty =>
+            doFromJson(
+              FromJsonArray(ctx, values, 0),
+              form,
+              cumulativeChars,
+              maxChars,
+              maxDepth
+            )
+          case JsNull | JsArray(_) | JsObject(_) =>
+            doFromJson(
+              ctx.next,
+              form,
+              cumulativeChars,
+              maxChars,
+              maxDepth
+            )
+          case simple =>
+            val value = simple match {
+              case JsString(v)  => v
+              case JsNumber(v)  => v.toString
+              case JsBoolean(v) => v.toString
+            }
+            val prefix             = ctx.prefix
+            val newCumulativeChars = cumulativeChars + prefix.length + value.length
+            doFromJson(ctx.next, form.updated(prefix, value), newCumulativeChars, maxChars, maxDepth)
+        }
+    }
   }
 
-  private sealed trait FromJsonContext
+  private sealed trait FromJsonContext {
+    def depth: Int
+  }
   private sealed trait FromJsonContextValue extends FromJsonContext {
     def value: JsValue
     def prefix: String
     def next: FromJsonContext
   }
-  private case object FromJsonTerm extends FromJsonContext
+  private case object FromJsonTerm extends FromJsonContext {
+    override def depth: Int = 0
+  }
   private case class FromJsonRoot(value: JsValue) extends FromJsonContextValue {
+    override def depth: Int            = 0
     override def prefix                = ""
     override def next: FromJsonContext = FromJsonTerm
   }
   private case class FromJsonArray(parent: FromJsonContextValue, values: scala.collection.IndexedSeq[JsValue], idx: Int)
       extends FromJsonContextValue {
+    override val depth: Int     = parent.depth + 1
     override def value: JsValue = values(idx)
     override val prefix: String = s"${parent.prefix}[$idx]"
     override lazy val next: FromJsonContext = if (idx + 1 < values.length) {
@@ -466,6 +518,7 @@ private[data] object FormUtils {
   }
   private case class FromJsonObject(parent: FromJsonContextValue, fields: IndexedSeq[(String, JsValue)], idx: Int)
       extends FromJsonContextValue {
+    override val depth: Int     = parent.depth + 1
     override def value: JsValue = fields(idx)._2
     override val prefix: String = if (parent.prefix.isEmpty) {
       fields(idx)._1
@@ -1053,6 +1106,10 @@ case class FormJsonExpansionTooLarge(limit: Long)
     extends RuntimeException(s"Binding form from JSON exceeds form expansion limit of $limit")
     with NoStackTrace
 
+case class FormJsonExpansionTooDeep(limit: Int)
+    extends RuntimeException(s"Binding form from JSON exceeds depth limit of $limit")
+    with NoStackTrace
+
 trait FormBinding {
   def apply(request: play.api.mvc.Request[_]): Map[String, Seq[String]]
 }
@@ -1066,11 +1123,13 @@ object FormBinding {
      *
      * Prefer using a FormBinding provided by PlayBodyParsers#formBinding since that honours play.http.parser.maxMemoryBuffer limits.
      */
-    implicit val formBinding: FormBinding = new DefaultFormBinding(Form.FromJsonMaxChars)
+    implicit val formBinding: FormBinding = new DefaultFormBinding(Form.FromJsonMaxChars, Form.FromJsonMaxDepth)
   }
 }
 
-class DefaultFormBinding(maxChars: Long) extends FormBinding {
+class DefaultFormBinding(maxChars: Long, maxDepth: Int) extends FormBinding {
+  def this(maxChars: Long) = this(maxChars, Form.FromJsonMaxDepth)
+
   def apply(request: play.api.mvc.Request[_]): Map[String, Seq[String]] = {
     import play.api.mvc.MultipartFormData
     val unwrap = request.body match {
@@ -1093,5 +1152,5 @@ class DefaultFormBinding(maxChars: Long) extends FormBinding {
   }
   private def multipartFormParse(body: MultipartFormData[_]) = body.asFormUrlEncoded
 
-  private def jsonParse(jsValue: JsValue) = FormUtils.fromJson(jsValue, maxChars).mapValues(Seq(_))
+  private def jsonParse(jsValue: JsValue) = FormUtils.fromJson(jsValue, maxChars, maxDepth).mapValues(Seq(_))
 }

core/play/src/main/scala/play/api/mvc/BodyParsers.scala

@@ -460,7 +460,8 @@ trait PlayBodyParsers extends BodyParserUtils {
 
   // -- General purpose
 
-  def formBinding(maxChars: Long = DefaultMaxTextLength): FormBinding = new DefaultFormBinding(maxChars)
+  def formBinding(maxChars: Long = DefaultMaxTextLength, maxDepth: Int = Form.FromJsonMaxDepth): FormBinding =
+    new DefaultFormBinding(maxChars, maxDepth)
 
   // -- Text parser
 

core/play/src/test/scala/play/api/data/FormUtilsSpec.scala

@@ -51,13 +51,13 @@ class FormUtilsSpec extends Specification {
         "j[0][0]"  -> "40",
       )
 
-      val map = FormUtils.fromJson(json, 1000)
+      val map = FormUtils.fromJson(json, 1000, 100)
       map.toSeq must containTheSameElementsAs(expected)
     }
 
     "not stack overflow when converting heavily nested arrays" in {
       try {
-        FormUtils.fromJson(Json.parse("{\"arr\":" + ("[" * 10000) + "1" + ("]" * 10000) + "}"), 1000000)
+        FormUtils.fromJson(Json.parse("{\"arr\":" + ("[" * 10000) + "1" + ("]" * 10000) + "}"), 1000000, 30000)
       } catch {
         case e: StackOverflowError =>
           ko("StackOverflowError thrown")
@@ -69,10 +69,12 @@ class FormUtilsSpec extends Specification {
       val keyLength = 10
       val itemCount = 10
       val maxChars  = 500 * 1000 // a limit we're not reaching
+      val maxDepth  = 100
       try {
         FormUtils.fromJson(
           Json.obj("a" * keyLength -> Json.arr(0 to itemCount)),
-          maxChars
+          maxChars,
+          maxDepth
         )
       } catch {
         case _: OutOfMemoryError =>
@@ -86,10 +88,12 @@ class FormUtilsSpec extends Specification {
       val keyLength = 10
       val itemCount = 10
       val maxChars  = 3 // yeah, maxChars is only 3 chars. We want to hit the limit.
+      val maxDepth  = 10
       (try {
         FormUtils.fromJson(
           Json.obj("a" * keyLength -> Json.arr(0 to itemCount)),
-          maxChars
+          maxChars,
+          maxDepth
         )
       } catch {
         case _: OutOfMemoryError =>
@@ -102,11 +106,13 @@ class FormUtilsSpec extends Specification {
       val keyLength = 10
       val itemCount = 10
       val maxChars  = 3 // yeah, maxChars is only 3 chars. We want to hit the limit.
+      val maxDepth  = 10
       (try {
         val jsString = Json.parse(s""" "${"a" * keyLength}" """)
         FormUtils.fromJson(
           jsString,
-          maxChars
+          maxChars,
+          maxDepth
         )
       } catch {
         case _: OutOfMemoryError =>
@@ -119,13 +125,15 @@ class FormUtilsSpec extends Specification {
       val keyLength = 10000
       val itemCount = 100000
       val maxChars  = keyLength // some value we're likely to exceed. We want this limit to kick in.
+      val maxDepth  = 100
       (try {
         FormUtils.fromJson(
           // A JSON object with a key of length 10000, pointing to a list with 100000 elements.
           // In memory, this will consume at most a few MB of space. When expanded, will consume
           // many GB of space.
           Json.obj("a" * keyLength -> Json.arr(0 to itemCount)),
-          maxChars
+          maxChars,
+          maxDepth
         )
       } catch {
         case _: OutOfMemoryError =>
@@ -135,6 +143,44 @@ class FormUtilsSpec extends Specification {
       }) must throwA[FormJsonExpansionTooLarge]
     }
 
+    "allow parsing array up to max depth" in {
+      try {
+        FormUtils.fromJson(Json.parse("{\"arr\":" + ("[" * 4) + "1" + ("]" * 4) + "}"), 1000000, 5)
+      } catch {
+        case e: StackOverflowError =>
+          ko("StackOverflowError thrown")
+      }
+      ok
+    }
+
+    "abort parsing array when max depth is exceeded" in {
+      (try {
+        FormUtils.fromJson(Json.parse("{\"arr\":" + ("[" * 5) + "1" + ("]" * 5) + "}"), 1000000, 5)
+      } catch {
+        case e: StackOverflowError =>
+          ko("StackOverflowError thrown")
+      }) must throwA[FormJsonExpansionTooDeep]
+    }
+
+    "allow parsing object up to max depth" in {
+      try {
+        FormUtils.fromJson(Json.parse(("{\"obj\":" * 5) + "1" + ("}" * 5)), 1000000, 5)
+      } catch {
+        case e: StackOverflowError =>
+          ko("StackOverflowError thrown")
+      }
+      ok
+    }
+
+    "abort parsing object when max depth is exceeded" in {
+      (try {
+        FormUtils.fromJson(Json.parse(("{\"obj\":" * 6) + "1" + ("}" * 6)), 1000000, 5)
+      } catch {
+        case e: StackOverflowError =>
+          ko("StackOverflowError thrown")
+      }) must throwA[FormJsonExpansionTooDeep]
+    }
+
   }
 
 }

web/play-java-forms/src/main/java/play/data/DynamicForm.java

@@ -292,7 +292,9 @@ public DynamicForm bind(
         attrs,
         play.libs.Scala.asJava(
             play.api.data.FormUtils.fromJson(
-                play.api.libs.json.Json.parse(play.libs.Json.stringify(data)), maxChars)),
+                play.api.libs.json.Json.parse(play.libs.Json.stringify(data)),
+                maxChars,
+                maxJsonDepth())),
         allowedFields);
   }