Avoid crashing with a StackOverflowException when iterating over the AllNodes property when it's infinitely recursive

YamlDotNet.Test/RepresentationModel/YamlStreamTests.cs

@@ -19,8 +19,11 @@
 //  OUT OF OR IN CONNECTION WITH THE SOFTWARE OR THE USE OR OTHER DEALINGS IN THE
 //  SOFTWARE.
 
+using FluentAssertions;
+using System;
 using System.Collections.Generic;
 using System.IO;
+using System.Linq;
 using System.Text;
 using Xunit;
 using YamlDotNet.Core;
@@ -42,6 +45,28 @@ public void LoadSimpleDocument()
             Assert.Equal(YamlNodeType.Scalar, stream.Documents[0].RootNode.NodeType);
         }
 
+        [Fact]
+        public void AccessingAllNodesOnInfinitelyRecursiveDocumentThrows()
+        {
+            var stream = new YamlStream();
+            stream.Load(Yaml.ParserForText("&a [*a]"));
+
+            var accessAllNodes = new Action(() => stream.Documents.Single().AllNodes.ToList());
+
+            accessAllNodes.ShouldThrow<MaximumRecursionLevelReachedException>("because the document is infinitely recursive.");
+        }
+
+        [Fact]
+        public void InfinitelyRecursiveNodeToStringSucceeds()
+        {
+            var stream = new YamlStream();
+            stream.Load(Yaml.ParserForText("&a [*a]"));
+
+            var toString = stream.Documents.Single().RootNode.ToString();
+
+            toString.Should().Contain(YamlNode.MaximumRecursionLevelReachedToStringValue);
+        }
+
         [Fact]
         public void BackwardAliasReferenceWorks()
         {

YamlDotNet/Core/MaximumRecursionLevelReachedException.cs

@@ -0,0 +1,81 @@
+//  This file is part of YamlDotNet - A .NET library for YAML.
+//  Copyright (c) Antoine Aubry and contributors
+
+//  Permission is hereby granted, free of charge, to any person obtaining a copy of
+//  this software and associated documentation files (the "Software"), to deal in
+//  the Software without restriction, including without limitation the rights to
+//  use, copy, modify, merge, publish, distribute, sublicense, and/or sell copies
+//  of the Software, and to permit persons to whom the Software is furnished to do
+//  so, subject to the following conditions:
+
+//  The above copyright notice and this permission notice shall be included in all
+//  copies or substantial portions of the Software.
+
+//  THE SOFTWARE IS PROVIDED "AS IS", WITHOUT WARRANTY OF ANY KIND, EXPRESS OR
+//  IMPLIED, INCLUDING BUT NOT LIMITED TO THE WARRANTIES OF MERCHANTABILITY,
+//  FITNESS FOR A PARTICULAR PURPOSE AND NONINFRINGEMENT. IN NO EVENT SHALL THE
+//  AUTHORS OR COPYRIGHT HOLDERS BE LIABLE FOR ANY CLAIM, DAMAGES OR OTHER
+//  LIABILITY, WHETHER IN AN ACTION OF CONTRACT, TORT OR OTHERWISE, ARISING FROM,
+//  OUT OF OR IN CONNECTION WITH THE SOFTWARE OR THE USE OR OTHER DEALINGS IN THE
+//  SOFTWARE.
+
+using System;
+using System.Runtime.Serialization;
+
+namespace YamlDotNet.Core
+{
+    /// <summary>
+    /// Exception that is thrown when an infinite recursion is detected.
+    /// </summary>
+    [Serializable]
+    public class MaximumRecursionLevelReachedException : YamlException
+    {
+        /// <summary>
+        /// Initializes a new instance of the <see cref="MaximumRecursionLevelReachedException"/> class.
+        /// </summary>
+        public MaximumRecursionLevelReachedException()
+        {
+        }
+
+        /// <summary>
+        /// Initializes a new instance of the <see cref="MaximumRecursionLevelReachedException"/> class.
+        /// </summary>
+        /// <param name="message">The message.</param>
+        public MaximumRecursionLevelReachedException(string message)
+            : base(message)
+        {
+        }
+
+        /// <summary>
+        /// Initializes a new instance of the <see cref="MaximumRecursionLevelReachedException"/> class.
+        /// </summary>
+        public MaximumRecursionLevelReachedException(Mark start, Mark end, string message)
+            : base(start, end, message)
+        {
+        }
+
+        /// <summary>
+        /// Initializes a new instance of the <see cref="MaximumRecursionLevelReachedException"/> class.
+        /// </summary>
+        /// <param name="message">The message.</param>
+        /// <param name="inner">The inner.</param>
+        public MaximumRecursionLevelReachedException(string message, Exception inner)
+            : base(message, inner)
+        {
+        }
+
+#if !(PORTABLE || UNITY)
+        /// <summary>
+        /// Initializes a new instance of the <see cref="MaximumRecursionLevelReachedException"/> class.
+        /// </summary>
+        /// <param name="info">The <see cref="T:System.Runtime.Serialization.SerializationInfo"/> that holds the serialized object data about the exception being thrown.</param>
+        /// <param name="context">The <see cref="T:System.Runtime.Serialization.StreamingContext"/> that contains contextual information about the source or destination.</param>
+        /// <exception cref="T:System.ArgumentNullException">The <paramref name="info"/> parameter is null. </exception>
+        /// <exception cref="T:System.Runtime.Serialization.SerializationException">The class name is null or <see cref="P:System.Exception.HResult"/> is zero (0). </exception>
+        protected MaximumRecursionLevelReachedException(SerializationInfo info, StreamingContext context)
+            : base(info, context)
+        {
+        }
+#endif
+    }
+}

YamlDotNet/Core/RecursionLevel.cs

@@ -0,0 +1,68 @@
+//  This file is part of YamlDotNet - A .NET library for YAML.
+//  Copyright (c) Antoine Aubry and contributors
+
+//  Permission is hereby granted, free of charge, to any person obtaining a copy of
+//  this software and associated documentation files (the "Software"), to deal in
+//  the Software without restriction, including without limitation the rights to
+//  use, copy, modify, merge, publish, distribute, sublicense, and/or sell copies
+//  of the Software, and to permit persons to whom the Software is furnished to do
+//  so, subject to the following conditions:
+
+//  The above copyright notice and this permission notice shall be included in all
+//  copies or substantial portions of the Software.
+
+//  THE SOFTWARE IS PROVIDED "AS IS", WITHOUT WARRANTY OF ANY KIND, EXPRESS OR
+//  IMPLIED, INCLUDING BUT NOT LIMITED TO THE WARRANTIES OF MERCHANTABILITY,
+//  FITNESS FOR A PARTICULAR PURPOSE AND NONINFRINGEMENT. IN NO EVENT SHALL THE
+//  AUTHORS OR COPYRIGHT HOLDERS BE LIABLE FOR ANY CLAIM, DAMAGES OR OTHER
+//  LIABILITY, WHETHER IN AN ACTION OF CONTRACT, TORT OR OTHERWISE, ARISING FROM,
+//  OUT OF OR IN CONNECTION WITH THE SOFTWARE OR THE USE OR OTHER DEALINGS IN THE
+//  SOFTWARE.
+
+namespace YamlDotNet.Core
+{
+    /// <summary>
+    /// Keeps track of the <see cref="Current"/> recursion level,
+    /// and throws <see cref="MaximumRecursionLevelReachedException"/>
+    /// whenever <see cref="Maximum"/> is reached.
+    /// </summary>
+    internal class RecursionLevel
+    {
+        public int Current { get; private set; }
+        public int Maximum { get; }
+
+        public RecursionLevel(int maximum)
+        {
+            Maximum = maximum;
+        }
+
+        /// <summary>
+        /// Increments the <see cref="Current"/> recursion level,
+        /// and throws <see cref="MaximumRecursionLevelReachedException"/>
+        /// if <see cref="Maximum"/> is reached.
+        /// </summary>
+        internal void Increment()
+        {
+            Current++;
+            if (Current >= Maximum)
+            {
+                throw new MaximumRecursionLevelReachedException();
+            }
+        }
+
+        /// <summary>
+        /// Increments the <see cref="Current"/> recursion level,
+        /// and returns whether <see cref="Current"/> is still less than <see cref="Maximum"/>.
+        /// </summary>
+        internal bool TryIncrement()
+        {
+            Current++;
+            return Current < Maximum;
+        }
+
+        internal void Decrement()
+        {
+            Current--;
+        }
+    }
+}

YamlDotNet/RepresentationModel/YamlAliasNode.cs

@@ -94,17 +94,19 @@ public override int GetHashCode()
         /// <returns>
         /// A <see cref="System.String"/> that represents this instance.
         /// </returns>
-        public override string ToString()
+        internal override string ToString(RecursionLevel level)
         {
             return "*" + Anchor;
         }
 
         /// <summary>
-        /// Gets all nodes from the document, starting on the current node.
+        /// Recursively enumerates all the nodes from the document, starting on the current node,
+        /// and throwing <see cref="MaximumRecursionLevelReachedException"/>
+        /// if <see cref="RecursionLevel.Maximum"/> is reached.
         /// </summary>
-        public override IEnumerable<YamlNode> AllNodes
+        internal override IEnumerable<YamlNode> SafeAllNodes(RecursionLevel level)
         {
-            get { yield return this; }
+            yield return this;
         }
 
         /// <summary>

YamlDotNet/RepresentationModel/YamlDocument.cs

@@ -79,13 +79,21 @@ internal YamlDocument(IParser parser)
             state.ResolveAliases();
 
 #if DEBUG
-            foreach (var node in AllNodes)
+            try
             {
-                if (node is YamlAliasNode)
+                foreach (var node in AllNodes)
                 {
-                    throw new InvalidOperationException("Error in alias resolution.");
+                    if (node is YamlAliasNode)
+                    {
+                        throw new InvalidOperationException("Error in alias resolution.");
+                    }
                 }
             }
+            catch (MaximumRecursionLevelReachedException)
+            {
+                // Silently absorb this exception.
+                // This is required to make some unit tests pass in DEBUG mode.
+            }
 #endif
 
             parser.Expect<DocumentEnd>();
@@ -195,6 +203,7 @@ public void Accept(IYamlVisitor visitor)
 
         /// <summary>
         /// Gets all nodes from the document.
+        /// <see cref="MaximumRecursionLevelReachedException"/> is thrown if an infinite recursion is detected.
         /// </summary>
         public IEnumerable<YamlNode> AllNodes
         {

YamlDotNet/RepresentationModel/YamlMappingNode.cs

@@ -320,25 +320,26 @@ public override int GetHashCode()
         }
 
         /// <summary>
-        /// Gets all nodes from the document, starting on the current node.
+        /// Recursively enumerates all the nodes from the document, starting on the current node,
+        /// and throwing <see cref="MaximumRecursionLevelReachedException"/>
+        /// if <see cref="RecursionLevel.Maximum"/> is reached.
         /// </summary>
-        public override IEnumerable<YamlNode> AllNodes
+        internal override IEnumerable<YamlNode> SafeAllNodes(RecursionLevel level)
         {
-            get
+            level.Increment();
+            yield return this;
+            foreach (var child in children)
             {
-                yield return this;
-                foreach (var child in children)
+                foreach (var node in child.Key.SafeAllNodes(level))
                 {
-                    foreach (var node in child.Key.AllNodes)
-                    {
-                        yield return node;
-                    }
-                    foreach (var node in child.Value.AllNodes)
-                    {
-                        yield return node;
-                    }
+                    yield return node;
+                }
+                foreach (var node in child.Value.SafeAllNodes(level))
+                {
+                    yield return node;
                 }
             }
+            level.Decrement();
         }
 
         /// <summary>
@@ -355,8 +356,13 @@ public override YamlNodeType NodeType
         /// <returns>
         /// A <see cref="System.String"/> that represents this instance.
         /// </returns>
-        public override string ToString()
+        internal override string ToString(RecursionLevel level)
         {
+            if (!level.TryIncrement())
+            {
+                return MaximumRecursionLevelReachedToStringValue;
+            }
+
             var text = new StringBuilder("{ ");
 
             foreach (var child in children)
@@ -365,11 +371,13 @@ public override string ToString()
                 {
                     text.Append(", ");
                 }
-                text.Append("{ ").Append(child.Key).Append(", ").Append(child.Value).Append(" }");
+                text.Append("{ ").Append(child.Key.ToString(level)).Append(", ").Append(child.Value.ToString(level)).Append(" }");
             }
 
             text.Append(" }");
 
+            level.Decrement();
+
             return text.ToString();
         }
 

YamlDotNet/RepresentationModel/YamlNode.cs

@@ -33,6 +33,9 @@ namespace YamlDotNet.RepresentationModel
     [Serializable]
     public abstract class YamlNode
     {
+        private const int MaximumRecursionLevel = 1000;
+        internal const string MaximumRecursionLevelReachedToStringValue = "WARNING! INFINITE RECURSION!";
+
         /// <summary>
         /// Gets or sets the anchor of the node.
         /// </summary>
@@ -196,14 +199,34 @@ protected static int CombineHashCodes(int h1, int h2)
             return unchecked(((h1 << 5) + h1) ^ h2);
         }
 
+        public override string ToString()
+        {
+            var level = new RecursionLevel(MaximumRecursionLevel);
+            return ToString(level);
+        }
+
+        internal abstract string ToString(RecursionLevel level);
+
         /// <summary>
         /// Gets all nodes from the document, starting on the current node.
+        /// <see cref="MaximumRecursionLevelReachedException"/> is thrown if an infinite recursion is detected.
         /// </summary>
-        public abstract IEnumerable<YamlNode> AllNodes
+        public IEnumerable<YamlNode> AllNodes
         {
-            get;
+            get
+            {
+                var level = new RecursionLevel(MaximumRecursionLevel);
+                return SafeAllNodes(level);
+            }
         }
 
+        /// <summary>
+        /// When implemented, recursively enumerates all the nodes from the document, starting on the current node.
+        /// If <see cref="RecursionLevel.Maximum"/> is reached, a <see cref="MaximumRecursionLevelReachedException"/> is thrown
+        /// instead of continuing and crashing with a <see cref="StackOverflowException"/>.
+        /// </summary>
+        internal abstract IEnumerable<YamlNode> SafeAllNodes(RecursionLevel level);
+
         /// <summary>
         /// Gets the type of node.
         /// </summary>

YamlDotNet/RepresentationModel/YamlScalarNode.cs

@@ -147,17 +147,19 @@ public static explicit operator string(YamlScalarNode value)
         /// <returns>
         /// A <see cref="System.String"/> that represents this instance.
         /// </returns>
-        public override string ToString()
+        internal override string ToString(RecursionLevel level)
         {
             return Value;
         }
 
         /// <summary>
-        /// Gets all nodes from the document, starting on the current node.
+        /// Recursively enumerates all the nodes from the document, starting on the current node,
+        /// and throwing <see cref="MaximumRecursionLevelReachedException"/>
+        /// if <see cref="RecursionLevel.Maximum"/> is reached.
         /// </summary>
-        public override IEnumerable<YamlNode> AllNodes
+        internal override IEnumerable<YamlNode> SafeAllNodes(RecursionLevel level)
         {
-            get { yield return this; }
+            yield return this;
         }
 
         /// <summary>