Browse code

fixed security issue in the sandbox

Fabien Potencier authored on 10/03/2019 17:31:18
Showing 6 changed files
... ...
@@ -1,5 +1,8 @@
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 * 1.38.0 (2019-XX-XX)
2 2
 
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+ * fixed sandbox security issue (under some circumstances, calling the
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+   __toString() method on an object was possible even if not allowed by the
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+   security policy)
3 6
  * fixed batch filter clobbers array keys when fill parameter is used
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  * added preserveKeys support for the batch filter
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  * fixed "embed" support when used from "template_from_string"
6 9
new file mode 100644
... ...
@@ -0,0 +1,42 @@
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+<?php
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+
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+/*
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+ * This file is part of Twig.
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+ *
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+ * (c) Fabien Potencier
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+ *
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+ * For the full copyright and license information, please view the LICENSE
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+ * file that was distributed with this source code.
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+ */
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+
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+namespace Twig\Node;
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+
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+use Twig\Compiler;
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+use Twig\Node\Expression\AbstractExpression;
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+
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+/**
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+ * Checks if casting an expression to __toString() is allowed by the sandbox.
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+ *
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+ * For instance, when there is a simple Print statement, like {{ article }},
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+ * and if the sandbox is enabled, we need to check that the __toString()
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+ * method is allowed if 'article' is an object. The same goes for {{ article|upper }}
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+ * or {{ random(article) }}
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+ *
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+ * @author Fabien Potencier <fabien@symfony.com>
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+ */
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+class CheckToStringNode extends Node
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+{
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+    public function __construct(AbstractExpression $expr)
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+    {
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+        parent::__construct(['expr' => $expr], [], $expr->getTemplateLine(), $expr->getNodeTag());
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+    }
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+
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+    public function compile(Compiler $compiler)
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+    {
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+        $compiler
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+            ->raw('$this->sandbox->ensureToStringAllowed(')
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+            ->subcompile($this->getNode('expr'))
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+            ->raw(')')
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+        ;
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+    }
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+}
... ...
@@ -22,6 +22,8 @@ use Twig\Node\Expression\FilterExpression;
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  * and if the sandbox is enabled, we need to check that the __toString()
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  * method is allowed if 'article' is an object.
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  *
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+ * Not used anymore, to be deprecated in 2.x and removed in 3.0
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+ *
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  * @author Fabien Potencier <fabien@symfony.com>
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  */
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 class SandboxedPrintNode extends PrintNode
... ...
@@ -13,13 +13,17 @@ namespace Twig\NodeVisitor;
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 use Twig\Environment;
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 use Twig\Node\CheckSecurityNode;
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+use Twig\Node\CheckToStringNode;
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+use Twig\Node\Expression\Binary\ConcatBinary;
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 use Twig\Node\Expression\Binary\RangeBinary;
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 use Twig\Node\Expression\FilterExpression;
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 use Twig\Node\Expression\FunctionExpression;
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+use Twig\Node\Expression\GetAttrExpression;
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+use Twig\Node\Expression\NameExpression;
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 use Twig\Node\ModuleNode;
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 use Twig\Node\Node;
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 use Twig\Node\PrintNode;
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-use Twig\Node\SandboxedPrintNode;
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+use Twig\Node\SetNode;
23 27
 
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 /**
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  * @final
... ...
@@ -33,6 +37,8 @@ class SandboxNodeVisitor extends AbstractNodeVisitor
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     protected $filters;
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     protected $functions;
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+    private $needsToStringWrap = false;
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+
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     protected function doEnterNode(Node $node, Environment $env)
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     {
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         if ($node instanceof ModuleNode) {
... ...
@@ -63,9 +69,28 @@ class SandboxNodeVisitor extends AbstractNodeVisitor
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                 $this->functions['range'] = $node;
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             }
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-            // wrap print to check __toString() calls
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             if ($node instanceof PrintNode) {
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-                return new SandboxedPrintNode($node->getNode('expr'), $node->getTemplateLine(), $node->getNodeTag());
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+                $this->needsToStringWrap = true;
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+                $this->wrapNode($node, 'expr');
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+            }
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+
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+            if ($node instanceof SetNode && !$node->getAttribute('capture')) {
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+                $this->needsToStringWrap = true;
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+            }
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+
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+            // wrap outer nodes that can implicitly call __toString()
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+            if ($this->needsToStringWrap) {
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+                if ($node instanceof ConcatBinary) {
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+                    $this->wrapNode($node, 'left');
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+                    $this->wrapNode($node, 'right');
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+                }
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+                if ($node instanceof FilterExpression) {
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+                    $this->wrapNode($node, 'node');
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+                    $this->wrapArrayNode($node, 'arguments');
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+                }
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+                if ($node instanceof FunctionExpression) {
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+                    $this->wrapArrayNode($node, 'arguments');
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+                }
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             }
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         }
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... ...
@@ -78,11 +103,31 @@ class SandboxNodeVisitor extends AbstractNodeVisitor
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             $this->inAModule = false;
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             $node->setNode('constructor_end', new Node([new CheckSecurityNode($this->filters, $this->tags, $this->functions), $node->getNode('display_start')]));
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+        } elseif ($this->inAModule) {
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+            if ($node instanceof PrintNode || $node instanceof SetNode) {
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+                $this->needsToStringWrap = false;
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+            }
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         }
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         return $node;
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     }
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+    private function wrapNode(Node $node, $name)
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+    {
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+        $expr = $node->getNode($name);
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+        if ($expr instanceof NameExpression || $expr instanceof GetAttrExpression) {
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+            $node->setNode($name, new CheckToStringNode($expr));
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+        }
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+    }
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+
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+    private function wrapArrayNode(Node $node, $name)
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+    {
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+        $args = $node->getNode($name);
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+        foreach ($args as $name => $_) {
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+            $this->wrapNode($args, $name);
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+        }
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+    }
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+
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     public function getPriority()
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     {
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         return 0;
... ...
@@ -34,7 +34,6 @@ class Twig_Tests_Extension_SandboxTest extends \PHPUnit\Framework\TestCase
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             '1_basic3' => '{% if name %}foo{% endif %}',
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             '1_basic4' => '{{ obj.bar }}',
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             '1_basic5' => '{{ obj }}',
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-            '1_basic6' => '{{ arr.obj }}',
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             '1_basic7' => '{{ cycle(["foo","bar"], 1) }}',
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             '1_basic8' => '{{ obj.getfoobar }}{{ obj.getFooBar }}',
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             '1_basic9' => '{{ obj.foobar }}{{ obj.fooBar }}',
... ...
@@ -112,11 +111,14 @@ class Twig_Tests_Extension_SandboxTest extends \PHPUnit\Framework\TestCase
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         }
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     }
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-    public function testSandboxUnallowedToString()
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+    /**
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+     * @dataProvider getSandboxUnallowedToStringTests
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+     */
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+    public function testSandboxUnallowedToString($template)
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     {
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-        $twig = $this->getEnvironment(true, [], self::$templates);
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+        $twig = $this->getEnvironment(true, [], ['index' => $template], [], ['upper'], ['FooObject' => 'getAnotherFooObject'], [], ['random']);
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         try {
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-            $twig->load('1_basic5')->render(self::$params);
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+            $twig->loadTemplate('index')->render(self::$params);
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             $this->fail('Sandbox throws a SecurityError exception if an unallowed method (__toString()) is called in the template');
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         } catch (SecurityError $e) {
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             $this->assertInstanceOf('\Twig\Sandbox\SecurityNotAllowedMethodError', $e, 'Exception should be an instance of Twig_Sandbox_SecurityNotAllowedMethodError');
... ...
@@ -125,17 +127,61 @@ class Twig_Tests_Extension_SandboxTest extends \PHPUnit\Framework\TestCase
125 127
         }
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     }
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-    public function testSandboxUnallowedToStringArray()
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+    public function getSandboxUnallowedToStringTests()
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     {
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-        $twig = $this->getEnvironment(true, [], self::$templates);
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-        try {
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-            $twig->load('1_basic6')->render(self::$params);
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-            $this->fail('Sandbox throws a SecurityError exception if an unallowed method (__toString()) is called in the template');
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-        } catch (SecurityError $e) {
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-            $this->assertInstanceOf('\Twig\Sandbox\SecurityNotAllowedMethodError', $e, 'Exception should be an instance of Twig_Sandbox_SecurityNotAllowedMethodError');
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-            $this->assertEquals('FooObject', $e->getClassName(), 'Exception should be raised on the "FooObject" class');
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-            $this->assertEquals('__tostring', $e->getMethodName(), 'Exception should be raised on the "__toString" method');
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-        }
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+        return [
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+            'simple' => ['{{ obj }}'],
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+            'object_from_array' => ['{{ arr.obj }}'],
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+            'object_chain' => ['{{ obj.anotherFooObject }}'],
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+            'filter' => ['{{ obj|upper }}'],
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+            'filter_from_array' => ['{{ arr.obj|upper }}'],
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+            'function' => ['{{ random(obj) }}'],
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+            'function_from_array' => ['{{ random(arr.obj) }}'],
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+            'function_and_filter' => ['{{ random(obj|upper) }}'],
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+            'function_and_filter_from_array' => ['{{ random(arr.obj|upper) }}'],
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+            'object_chain_and_filter' => ['{{ obj.anotherFooObject|upper }}'],
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+            'object_chain_and_function' => ['{{ random(obj.anotherFooObject) }}'],
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+            'concat' => ['{{ obj ~ "" }}'],
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+            'concat_again' => ['{{ "" ~ obj }}'],
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+        ];
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+    }
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+
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+    /**
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+     * @dataProvider getSandboxAllowedToStringTests
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+     */
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+    public function testSandboxAllowedToString($template, $output)
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+    {
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+        $twig = $this->getEnvironment(true, [], ['index' => $template], ['set'], [], ['FooObject' => ['foo', 'getAnotherFooObject']]);
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+        $this->assertEquals($output, $twig->load('index')->render(self::$params));
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+    }
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+
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+    public function getSandboxAllowedToStringTests()
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+    {
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+        return [
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+            'constant_test' => ['{{ obj is constant("PHP_INT_MAX") }}', ''],
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+            'set_object' => ['{% set a = obj.anotherFooObject %}{{ a.foo }}', 'foo'],
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+            'is_defined' => ['{{ obj.anotherFooObject is defined }}', '1'],
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+            'is_null' => ['{{ obj is null }}', ''],
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+            'is_sameas' => ['{{ obj is same as(obj) }}', '1'],
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+            'is_sameas_from_array' => ['{{ arr.obj is same as(arr.obj) }}', '1'],
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+            'is_sameas_from_another_method' => ['{{ obj.anotherFooObject is same as(obj.anotherFooObject) }}', ''],
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+        ];
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+    }
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+
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+    public function testSandboxAllowMethodToString()
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+    {
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+        $twig = $this->getEnvironment(true, [], self::$templates, [], [], ['FooObject' => '__toString']);
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+        FooObject::reset();
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+        $this->assertEquals('foo', $twig->load('1_basic5')->render(self::$params), 'Sandbox allow some methods');
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+        $this->assertEquals(1, FooObject::$called['__toString'], 'Sandbox only calls method once');
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+    }
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+
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+    public function testSandboxAllowMethodToStringDisabled()
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+    {
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+        $twig = $this->getEnvironment(false, [], self::$templates);
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+        FooObject::reset();
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+        $this->assertEquals('foo', $twig->load('1_basic5')->render(self::$params), 'Sandbox allows __toString when sandbox disabled');
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+        $this->assertEquals(1, FooObject::$called['__toString'], 'Sandbox only calls method once');
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     }
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     public function testSandboxUnallowedFunction()
... ...
@@ -170,22 +216,6 @@ class Twig_Tests_Extension_SandboxTest extends \PHPUnit\Framework\TestCase
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         $this->assertEquals(1, FooObject::$called['foo'], 'Sandbox only calls method once');
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     }
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-    public function testSandboxAllowMethodToString()
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-    {
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-        $twig = $this->getEnvironment(true, [], self::$templates, [], [], ['FooObject' => '__toString']);
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-        FooObject::reset();
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-        $this->assertEquals('foo', $twig->load('1_basic5')->render(self::$params), 'Sandbox allow some methods');
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-        $this->assertEquals(1, FooObject::$called['__toString'], 'Sandbox only calls method once');
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-    }
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-
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-    public function testSandboxAllowMethodToStringDisabled()
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-    {
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-        $twig = $this->getEnvironment(false, [], self::$templates);
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-        FooObject::reset();
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-        $this->assertEquals('foo', $twig->load('1_basic5')->render(self::$params), 'Sandbox allows __toString when sandbox disabled');
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-        $this->assertEquals(1, FooObject::$called['__toString'], 'Sandbox only calls method once');
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-    }
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-
189 219
     public function testSandboxAllowFilter()
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     {
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         $twig = $this->getEnvironment(true, [], self::$templates, [], ['upper']);
... ...
@@ -326,4 +356,9 @@ class FooObject
326 356
 
327 357
         return 'foobar';
328 358
     }
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+
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+    public function getAnotherFooObject()
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+    {
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+        return new self();
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+    }
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 }
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deleted file mode 100644
... ...
@@ -1,42 +0,0 @@
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-<?php
2
-
3
-/*
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- * This file is part of Twig.
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- *
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- * (c) Fabien Potencier
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- *
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- * For the full copyright and license information, please view the LICENSE
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- * file that was distributed with this source code.
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- */
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-
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-use Twig\Node\Expression\ConstantExpression;
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-use Twig\Node\Expression\NameExpression;
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-use Twig\Node\SandboxedPrintNode;
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-use Twig\Test\NodeTestCase;
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-
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-class Twig_Tests_Node_SandboxedPrintTest extends NodeTestCase
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-{
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-    public function testConstructor()
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-    {
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-        $node = new SandboxedPrintNode($expr = new ConstantExpression('foo', 1), 1);
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-
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-        $this->assertEquals($expr, $node->getNode('expr'));
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-    }
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-
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-    public function getTests()
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-    {
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-        $tests[] = [new SandboxedPrintNode(new ConstantExpression('foo', 1), 1), <<<EOF
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-// line 1
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-echo "foo";
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-EOF
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-        ];
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-
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-        $tests[] = [new SandboxedPrintNode(new NameExpression('foo', 1), 1), <<<EOF
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-// line 1
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-echo \$this->env->getExtension('\Twig\Extension\SandboxExtension')->ensureToStringAllowed({$this->getVariableGetter('foo', false)});
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-EOF
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-        ];
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-
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-        return $tests;
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-    }
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-}