Add documentation for form limits & improve configuration via context attributes

documentation/jetty/modules/code/examples/src/main/java/org/eclipse/jetty/docs/programming/security/FormSizeDocs.java

@@ -0,0 +1,30 @@
+//
+// ========================================================================
+// Copyright (c) 1995 Mort Bay Consulting Pty Ltd and others.
+//
+// This program and the accompanying materials are made available under the
+// terms of the Eclipse Public License v. 2.0 which is available at
+// https://www.eclipse.org/legal/epl-2.0, or the Apache License, Version 2.0
+// which is available at https://www.apache.org/licenses/LICENSE-2.0.
+//
+// SPDX-License-Identifier: EPL-2.0 OR Apache-2.0
+// ========================================================================
+//
+
+package org.eclipse.jetty.docs.programming.security;
+
+import org.eclipse.jetty.ee10.servlet.ServletContextHandler;
+
+public class FormSizeDocs
+{
+    public void example()
+    {
+        ServletContextHandler servletContextHandler = new ServletContextHandler();
+        int maxSizeInBytes = 1024;
+        int formKeys = 100;
+        // tag::formSizeConfig[]
+        servletContextHandler.setMaxFormContentSize(maxSizeInBytes);
+        servletContextHandler.setMaxFormKeys(formKeys);
+        // end::formSizeConfig[]
+    }
+}

documentation/jetty/modules/programming-guide/nav.adoc

@@ -43,6 +43,8 @@
 ** xref:troubleshooting/state-tracking.adoc[]
 ** xref:troubleshooting/component-dump.adoc[]
 ** xref:troubleshooting/debugging.adoc[]
+* Jetty Security
+** xref:security/configuring-form-size.adoc[]
 * Migration Guides
 ** xref:migration/94-to-10.adoc[]
 ** xref:migration/11-to-12.adoc[]

documentation/jetty/modules/programming-guide/pages/security/configuring-form-size.adoc

@@ -0,0 +1,56 @@
+//
+// ========================================================================
+// Copyright (c) 1995 Mort Bay Consulting Pty Ltd and others.
+//
+// This program and the accompanying materials are made available under the
+// terms of the Eclipse Public License v. 2.0 which is available at
+// https://www.eclipse.org/legal/epl-2.0, or the Apache License, Version 2.0
+// which is available at https://www.apache.org/licenses/LICENSE-2.0.
+//
+// SPDX-License-Identifier: EPL-2.0 OR Apache-2.0
+// ========================================================================
+//
+
+[[configuring-form-size]]
+= Limiting Form Content
+
+Form content sent to the server is processed by Jetty into a map of parameters to be used by the web application.
+This can be vulnerable to denial of service (DOS) attacks since significant memory and CPU can be consumed if a malicious clients sends very large form content or large number of form keys.
+Thus, Jetty limits the amount of data and keys that can be in a form posted to Jetty.
+
+The default maximum size Jetty permits is 200000 bytes and 1000 keys.
+You can change this default for a particular webapp or for all webapps on a particular Server instance.
+
+== Configuring Form Limits for a Webapp
+
+To configure the form limits for a single web application, the servlet context handler (or webappContext) instance must be configured using the following methods:
+
+[,java,indent=0]
+----
+include::code:example$src/main/java/org/eclipse/jetty/docs/programming/security/FormSizeDocs.java[tags=formSizeConfig]
+----
+
+These methods may be called directly when embedding Jetty, but more commonly are configured from a context XML file or WEB-INF/jetty-web.xml file:
+
+[,xml,subs=attributes+]
+----
+<Configure class="org.eclipse.jetty.{ee-current}.webapp.WebAppContext">
+
+  ...
+
+  <Set name="maxFormContentSize">200000</Set>
+  <Set name="maxFormKeys">200</Set>
+</Configure>
+
+----
+
+These settings can also be set via the following Context attributes.
+
+- `org.eclipse.jetty.server.Request.maxFormKeys`
+- `org.eclipse.jetty.server.Request.maxFormContentSize`
+
+== Configuring Default Form Limits for the Server
+
+The default `maxFormKeys` is 1000 and the default `maxFormContentSize` is 200000.
+
+However, the following system properties can be set to change the default values of this across every context; `org.eclipse.jetty.server.Request.maxFormKeys` and `org.eclipse.jetty.server.Request.maxFormContentSize`.

jetty-ee10/jetty-ee10-servlet/src/main/java/org/eclipse/jetty/ee10/servlet/ServletContextHandler.java

@@ -319,6 +319,8 @@ public InvocationType getInvocationType()
     public void dump(Appendable out, String indent) throws IOException
     {
         dumpObjects(out, indent,
+            Dumpable.named("maxFormKeys ", getMaxFormKeys()),
+            Dumpable.named("maxFormContentSize ", getMaxFormContentSize()),
             new ClassLoaderDump(getClassLoader()),
             Dumpable.named("context " + this, getContext()),
             Dumpable.named("handler attributes " + this, getContext().getPersistentAttributes()),
@@ -2045,6 +2047,44 @@ public void setExtendedListenerTypes(boolean b)
         {
             _servletContext.setExtendedListenerTypes(b);
         }
+
+        @Override
+        public Object getAttribute(String name)
+        {
+            return switch (name)
+            {
+                case FormFields.MAX_FIELDS_ATTRIBUTE -> getMaxFormKeys();
+                case FormFields.MAX_LENGTH_ATTRIBUTE -> getMaxFormContentSize();
+                default -> super.getAttribute(name);
+            };
+        }
+
+        @Override
+        public Object setAttribute(String name, Object attribute)
+        {
+            return switch (name)
+            {
+                case FormFields.MAX_FIELDS_ATTRIBUTE ->
+                {
+                    int oldValue = getMaxFormKeys();
+                    if (attribute == null)
+                        setMaxFormKeys(DEFAULT_MAX_FORM_KEYS);
+                    else
+                        setMaxFormKeys(Integer.parseInt(attribute.toString()));
+                    yield oldValue;
+                }
+                case FormFields.MAX_LENGTH_ATTRIBUTE ->
+                {
+                    int oldValue = getMaxFormContentSize();
+                    if (attribute == null)
+                        setMaxFormContentSize(DEFAULT_MAX_FORM_CONTENT_SIZE);
+                    else
+                        setMaxFormContentSize(Integer.parseInt(attribute.toString()));
+                    yield oldValue;
+                }
+                default -> super.setAttribute(name, attribute);
+            };
+        }
     }
 
     public class ServletContextApi implements jakarta.servlet.ServletContext

jetty-ee10/jetty-ee10-webapp/src/main/java/org/eclipse/jetty/ee10/webapp/WebAppContext.java

@@ -57,6 +57,7 @@
 import org.eclipse.jetty.util.annotation.ManagedAttribute;
 import org.eclipse.jetty.util.annotation.ManagedObject;
 import org.eclipse.jetty.util.component.ClassLoaderDump;
+import org.eclipse.jetty.util.component.Dumpable;
 import org.eclipse.jetty.util.component.DumpableCollection;
 import org.eclipse.jetty.util.resource.Resource;
 import org.eclipse.jetty.util.resource.ResourceFactory;
@@ -987,6 +988,8 @@ else if (getBaseResource() != null)
         name = String.format("%s@%x", name, hashCode());
 
         dumpObjects(out, indent,
+            Dumpable.named("maxFormKeys ", getMaxFormKeys()),
+            Dumpable.named("maxFormContentSize ", getMaxFormContentSize()),
             new ClassLoaderDump(getClassLoader()),
             new DumpableCollection("Systemclasses " + name, systemClasses),
             new DumpableCollection("Serverclasses " + name, serverClasses),

jetty-ee9/jetty-ee9-nested/src/main/java/org/eclipse/jetty/ee9/nested/ContextHandler.java

@@ -94,6 +94,7 @@
 import org.eclipse.jetty.util.URIUtil;
 import org.eclipse.jetty.util.annotation.ManagedAttribute;
 import org.eclipse.jetty.util.annotation.ManagedObject;
+import org.eclipse.jetty.util.component.Dumpable;
 import org.eclipse.jetty.util.component.DumpableCollection;
 import org.eclipse.jetty.util.component.Environment;
 import org.eclipse.jetty.util.component.LifeCycle;
@@ -302,7 +303,10 @@ public void insertHandler(org.eclipse.jetty.server.Handler.Singleton coreHandler
     @Override
     public void dump(Appendable out, String indent) throws IOException
     {
-        dumpObjects(out, indent, new DumpableCollection("initparams " + this, getInitParams().entrySet()));
+        dumpObjects(out, indent,
+            Dumpable.named("maxFormKeys ", getMaxFormKeys()),
+            Dumpable.named("maxFormContentSize ", getMaxFormContentSize()),
+            new DumpableCollection("initparams " + this, getInitParams().entrySet()));
     }
 
     public APIContext getServletContext()
@@ -2861,6 +2865,44 @@ public APIContext getAPIContext()
             {
                 return _apiContext;
             }
+
+            @Override
+            public Object getAttribute(String name)
+            {
+                return switch (name)
+                {
+                    case FormFields.MAX_FIELDS_ATTRIBUTE -> getMaxFormKeys();
+                    case FormFields.MAX_LENGTH_ATTRIBUTE -> getMaxFormContentSize();
+                    default -> super.getAttribute(name);
+                };
+            }
+
+            @Override
+            public Object setAttribute(String name, Object attribute)
+            {
+                return switch (name)
+                {
+                    case FormFields.MAX_FIELDS_ATTRIBUTE ->
+                    {
+                        int oldValue = getMaxFormKeys();
+                        if (attribute == null)
+                            setMaxFormKeys(DEFAULT_MAX_FORM_KEYS);
+                        else
+                            setMaxFormKeys(Integer.parseInt(attribute.toString()));
+                        yield oldValue;
+                    }
+                    case FormFields.MAX_LENGTH_ATTRIBUTE ->
+                    {
+                        int oldValue = getMaxFormContentSize();
+                        if (attribute == null)
+                            setMaxFormContentSize(DEFAULT_MAX_FORM_CONTENT_SIZE);
+                        else
+                            setMaxFormContentSize(Integer.parseInt(attribute.toString()));
+                        yield oldValue;
+                    }
+                    default -> super.setAttribute(name, attribute);
+                };
+            }
         }
 
         private class CoreToNestedHandler extends Abstract

jetty-ee9/jetty-ee9-webapp/src/main/java/org/eclipse/jetty/ee9/webapp/WebAppContext.java

@@ -945,6 +945,8 @@ else if (getResourceBase() != null)
 
         dumpObjects(out, indent,
             Dumpable.named("environment", ContextHandler.ENVIRONMENT.getName()),
+            Dumpable.named("maxFormKeys ", getMaxFormKeys()),
+            Dumpable.named("maxFormContentSize ", getMaxFormContentSize()),
             new ClassLoaderDump(getClassLoader()),
             new DumpableCollection("Systemclasses " + name, systemClasses),
             new DumpableCollection("Serverclasses " + name, serverClasses),