Imported Upstream version 4.6.0.125

Former-commit-id: a2155e9bd80020e49e72e86c44da02a8ac0e57a4

mcs/class/referencesource/System.Web/Util/XmlUtils.cs

@@ -0,0 +1,240 @@
+//------------------------------------------------------------------------------
+// <copyright file="XmlUtils.cs" company="Microsoft">
+//     Copyright (c) Microsoft Corporation.  All rights reserved.
+// </copyright>
+//------------------------------------------------------------------------------
+
+namespace System.Web.Util {
+
+    using System.IO;
+    using System.Xml;
+    using System.Xml.XPath;
+    using System.Xml.Xsl;
+    using System.Diagnostics.CodeAnalysis;
+
+    internal static class XmlUtils
+    {
+        public static readonly long MaxEntityExpansion = 1024 * 1024;
+
+        [SuppressMessage("Microsoft.Security", "MSEC1208:DoNotUseLoadXml", Justification = "Handles developer-controlled input xml.  Optional safer codepath available via appSettings/aspnet:RestrictXmlControls configuration.")]
+        public static XmlDocument CreateXmlDocumentFromContent(string content)
+        {
+            XmlDocument doc = new XmlDocument();
+
+           if (AppSettings.RestrictXmlControls) {
+                // We can't use the simple XmlDocument.LoadXml(string) here because there is no way to control the
+                // resolver used in that process.  The only way we can do that is if we pass in our own XmlReader.
+                using (StringReader sreader = new StringReader(content)) {
+                    doc.Load(CreateXmlReader(sreader));
+                }
+            }
+            else {
+                doc.LoadXml(content);
+            }
+            return doc;
+        }
+
+        [SuppressMessage("Microsoft.Security", "MSEC1210:UseXmlReaderForXPathDocument", Justification = "Handles developer-controlled input xml.  Optional safer codepath available via appSettings/aspnet:RestrictXmlControls configuration.")]
+        public static XPathDocument CreateXPathDocumentFromContent(string content)
+        {
+            StringReader reader = new StringReader(content);
+            if (AppSettings.RestrictXmlControls) {
+                return new XPathDocument(CreateXmlReader(reader));
+            }
+            else {
+                return new XPathDocument(reader);
+            }
+        }
+
+        [SuppressMessage("Microsoft.Security", "MSEC1220:ReviewDtdProcessingAssignment", Justification = "Dtd processing is needed for back-compat, but is being done as safely as possible.")]
+        public static XmlReaderSettings CreateXmlReaderSettings()
+        {
+            XmlReaderSettings settings = new XmlReaderSettings();
+            if (AppSettings.RestrictXmlControls)
+            {
+                settings.MaxCharactersFromEntities = XmlUtils.MaxEntityExpansion;
+                settings.XmlResolver = null;
+                // Prohibit is the default here.  We don't need to prohibit DTD's, or even ignore them if we're using
+                // RestrictXmlControls, because we use a null resolver and limit/disable entity expansion.
+                settings.DtdProcessing = DtdProcessing.Parse;
+            }
+            return settings;
+        }
+
+        // Ideally, these XmlReader factories would use XmlReader.Create() in the non-RestrictXmlControls case,
+        // but the default settings on that method are different from the default settings generated by XmlTextReader
+        // constructors, which is the code we're replacing with these factories.  Since we want to keep doing
+        // whatever it was that we did before in this case, we'll just new up an XmlTextReader rather than
+        // try to guess at how to set matching defaults with XmlReader.Create().
+        // (E.g. DtdProcessing is Parse by default using XmlTextReader directly.  It's Prohibit in default XmlReaderSettings.)
+        [SuppressMessage("Microsoft.Security", "MSEC1205:DoNotAllowDtdOnXmlTextReader", Justification = "Handles trusted or developer-controlled input xml.  Optional safer codepath available via appSettings/aspnet:RestrictXmlControls configuration.")]
+        [SuppressMessage("Microsoft.Security", "MSEC1225:ReviewClassesDerivedFromXmlTextReader", Justification = "NoEntitiesXmlReader is our internal mechanism for using XmlTextReaders in a reasonably safe manner.")]
+        public static XmlReader CreateXmlReader(string filepath)
+        {
+            if (AppSettings.RestrictXmlControls)
+            {
+                NoEntitiesXmlTextReader nextr = new NoEntitiesXmlTextReader(filepath);
+                return XmlReader.Create(nextr, CreateXmlReaderSettings());
+            }
+            else
+            {
+                XmlTextReader xtr = new XmlTextReader(filepath);
+                return xtr;
+            }
+        }
+
+        [SuppressMessage("Microsoft.Security", "MSEC1205:DoNotAllowDtdOnXmlTextReader", Justification = "Handles trusted or developer-controlled input xml.  Optional safer codepath available via appSettings/aspnet:RestrictXmlControls configuration.")]
+        [SuppressMessage("Microsoft.Security", "MSEC1225:ReviewClassesDerivedFromXmlTextReader", Justification = "NoEntitiesXmlReader is our internal mechanism for using XmlTextReaders in a reasonably safe manner.")]
+        public static XmlReader CreateXmlReader(Stream datastream)
+        {
+            if (AppSettings.RestrictXmlControls)
+            {
+                NoEntitiesXmlTextReader nextr = new NoEntitiesXmlTextReader(datastream);
+                return XmlReader.Create(nextr, CreateXmlReaderSettings());
+            }
+            else
+            {
+                XmlTextReader xtr = new XmlTextReader(datastream);
+                return xtr;
+            }
+        }
+
+        [SuppressMessage("Microsoft.Security", "MSEC1205:DoNotAllowDtdOnXmlTextReader", Justification = "Handles trusted or developer-controlled input xml.  Optional safer codepath available via appSettings/aspnet:RestrictXmlControls configuration.")]
+        [SuppressMessage("Microsoft.Security", "MSEC1225:ReviewClassesDerivedFromXmlTextReader", Justification = "NoEntitiesXmlReader is our internal mechanism for using XmlTextReaders in a reasonably safe manner.")]
+        public static XmlReader CreateXmlReader(TextReader reader)
+        {
+            if (AppSettings.RestrictXmlControls)
+            {
+                NoEntitiesXmlTextReader nextr = new NoEntitiesXmlTextReader(reader);
+                return XmlReader.Create(nextr, CreateXmlReaderSettings());
+            }
+            else
+            {
+                XmlTextReader xtr = new XmlTextReader(reader);
+                return xtr;
+            }
+        }
+
+        [SuppressMessage("Microsoft.Security", "MSEC1205:DoNotAllowDtdOnXmlTextReader", Justification = "Handles trusted or developer-controlled input xml.  Optional safer codepath available via appSettings/aspnet:RestrictXmlControls configuration.")]
+        [SuppressMessage("Microsoft.Security", "MSEC1225:ReviewClassesDerivedFromXmlTextReader", Justification = "NoEntitiesXmlReader is our internal mechanism for using XmlTextReaders in a reasonably safe manner.")]
+        public static XmlReader CreateXmlReader(Stream contentStream, string baseURI)
+        {
+            if (AppSettings.RestrictXmlControls)
+            {
+                NoEntitiesXmlTextReader nextr = new NoEntitiesXmlTextReader(baseURI, contentStream);
+                return XmlReader.Create(nextr, CreateXmlReaderSettings());
+            }
+            else
+            {
+                XmlTextReader xtr = new XmlTextReader(baseURI, contentStream);
+                return xtr;
+            }
+        }
+
+        // If you use any of these overloads that take in XmlReaderSettings, the suggestion is to get your base settings from
+        // CreateXmlReaderSettings().  That way you will have the correct defaults for RestrictXmlControls if applicable.
+        // Then you need to be smart about which settings you change before passing in here, because we will not
+        // re-enforce the correct settings, just in case you intentionally meant to change them.
+        public static XmlReader CreateXmlReader(TextReader reader, string baseURI, XmlReaderSettings settings)
+        {
+            if (settings == null) {
+                settings = CreateXmlReaderSettings();
+            }
+
+            // Note:  If there is nothing materially changed in the settings, then Create() will just return your reader back
+            // to you and reader.Settings might still be null.
+            return XmlReader.Create(reader, settings, baseURI);
+        }
+
+        public static XslCompiledTransform CreateXslCompiledTransform(XmlReader xmlReader)
+        {
+            XmlReader readerToUse = xmlReader;
+
+            // XslCompiledTransform reconstructs its own XmlReader from scratch, so we can't rely entirely on the fancy
+            // protections we have in place on our readers.  We need to bring out a bigger hammer and disable DTD's
+            // alltogether.  We know how to work with XmlTextReader and which of its settings XslCompiledTransform will
+            // respect.  For other reader types, just try to wrap it with new settings.
+            if (AppSettings.RestrictXmlControls) {
+                XmlTextReader xtr = xmlReader as XmlTextReader;
+                if (xtr != null) {
+                    xtr.DtdProcessing = DtdProcessing.Ignore;
+                }
+                else {
+                    XmlReaderSettings settings = xmlReader.Settings;
+                    if (settings == null) {
+                        settings = CreateXmlReaderSettings();
+                    }
+                    settings.DtdProcessing = DtdProcessing.Ignore;
+                    readerToUse = XmlReader.Create(xmlReader, settings);
+                }
+            }
+
+            XslCompiledTransform compiledTransform = new XslCompiledTransform();
+            // The second parameter is XsltSettings.  null results in the XsltSettings.Default being used, which disables the document function, and script
+            // The third parameter is an XmlResolver to be used
+            compiledTransform.Load(readerToUse, null, null);
+            return compiledTransform;
+        }
+
+
+#pragma warning disable 0618    // To avoid deprecation warning
+        [SuppressMessage("Microsoft.Security", "MSEC1201:DoNotUseXslTransform", Justification = "Handles developer-controlled input xsl.  Optional safer codepath available via appSettings/aspnet:RestrictXmlControls configuration.")]
+        public static XslTransform CreateXslTransform(XmlReader reader)
+        {
+            if (!AppSettings.RestrictXmlControls)
+            {
+                XslTransform xform = new XslTransform();
+                xform.Load(reader);
+                return xform;
+            }
+            return null;
+        }
+
+        [SuppressMessage("Microsoft.Security", "MSEC1201:DoNotUseXslTransform", Justification = "Handles developer-controlled input xsl.  Optional safer codepath available via appSettings/aspnet:RestrictXmlControls configuration.")]
+        public static XslTransform CreateXslTransform(XmlReader reader, XmlResolver resolver)
+        {
+            if (!AppSettings.RestrictXmlControls)
+            {
+                XslTransform xform = new XslTransform();
+                xform.Load(reader, resolver, null);
+                return xform;
+            }
+            return null;
+        }
+
+        public static XslTransform GetXslTransform(XslTransform xform)
+        {
+            return (AppSettings.RestrictXmlControls ? null : xform);
+        }
+#pragma warning restore 0618
+
+        // This class exists to override the ResolveEntity() method, which can be used to force resolution of custom/external
+        // entities in Xml files.  When we use this class, we should have already set EntityHandling to EntityHandling.ExpandCharEntities,
+        // which will disable custom/external entity expansion by default.  But this extra protection will keep people from unintentionally
+        // shooting themselves in the foot when they think they might have been safe.
+        private sealed class NoEntitiesXmlTextReader : XmlTextReader
+        {
+            [SuppressMessage("Microsoft.Security", "MSEC1205:DoNotAllowDtdOnXmlTextReader", Justification = "Handles developer-controlled input xml.  Optional safer codepath available via appSettings/aspnet:RestrictXmlControls configuration.")]
+            public NoEntitiesXmlTextReader() : base() { Restrict(); }
+            [SuppressMessage("Microsoft.Security", "MSEC1205:DoNotAllowDtdOnXmlTextReader", Justification = "Handles developer-controlled input xml.  Optional safer codepath available via appSettings/aspnet:RestrictXmlControls configuration.")]
+            public NoEntitiesXmlTextReader(string filepath) : base(filepath) { Restrict(); }
+            [SuppressMessage("Microsoft.Security", "MSEC1205:DoNotAllowDtdOnXmlTextReader", Justification = "Handles developer-controlled input xml.  Optional safer codepath available via appSettings/aspnet:RestrictXmlControls configuration.")]
+            public NoEntitiesXmlTextReader(TextReader reader) : base(reader) { Restrict(); }
+            [SuppressMessage("Microsoft.Security", "MSEC1205:DoNotAllowDtdOnXmlTextReader", Justification = "Handles developer-controlled input xml.  Optional safer codepath available via appSettings/aspnet:RestrictXmlControls configuration.")]
+            public NoEntitiesXmlTextReader(Stream datastream) : base(datastream) { Restrict(); }
+            [SuppressMessage("Microsoft.Security", "MSEC1205:DoNotAllowDtdOnXmlTextReader", Justification = "Handles developer-controlled input xml.  Optional safer codepath available via appSettings/aspnet:RestrictXmlControls configuration.")]
+            public NoEntitiesXmlTextReader(string baseURI, Stream contentStream) : base(baseURI, contentStream) { Restrict(); }
+
+            public override void ResolveEntity()
+            {
+                // Do not ever do general entity expansion/replacement, even when asked
+                return;
+            }
+
+            private void Restrict() {
+                EntityHandling = EntityHandling.ExpandCharEntities;
+                XmlResolver = null;
+            }
+        }
+    }
+}