Merge pull request github#11869 from alexrford/rails/render_locals_shared

Ruby: Rails - generalize rails flow step for accessing render locals hash in view

Author: alexrford

ruby/ql/lib/change-notes/2023-01-13-flow-through-render-locals.md

@@ -0,0 +1,4 @@
+---
+category: minorAnalysis
+---
+* Data flowing from the `locals` argument of a Rails `render` call is now tracked to uses of that data in an associated view.

ruby/ql/lib/codeql/ruby/dataflow/FlowSummary.qll

@@ -30,6 +30,8 @@ module SummaryComponent {
 
   predicate withContent = SC::withContent/1;
 
+  class SyntheticGlobal = SC::SyntheticGlobal;
+
   /** Gets a summary component that represents a receiver. */
   SummaryComponent receiver() { result = argument(any(ParameterPosition pos | pos.isSelf())) }
 

ruby/ql/lib/codeql/ruby/frameworks/Rails.qll

@@ -10,6 +10,43 @@ private import codeql.ruby.frameworks.ActiveStorage
 private import codeql.ruby.frameworks.internal.Rails
 private import codeql.ruby.ApiGraphs
 private import codeql.ruby.security.OpenSSL
+private import codeql.ruby.dataflow.FlowSummary
+
+/** Provides utility predicates for extracting information from calls to `render`. */
+private module RenderCallUtils {
+  private Expr getTemplatePathArgument(MethodCall renderCall) {
+    // TODO: support other ways of specifying paths (e.g. `file`)
+    result =
+      [renderCall.getKeywordArgument(["partial", "template", "action"]), renderCall.getArgument(0)]
+  }
+
+  private string getTemplatePathValue(MethodCall renderCall) {
+    result = getTemplatePathArgument(renderCall).getConstantValue().getStringlikeValue()
+  }
+
+  // everything up to and including the final slash, but ignoring any leading slash
+  private string getSubPath(MethodCall renderCall) {
+    result = getTemplatePathValue(renderCall).regexpCapture("^/?(.*/)?(?:[^/]*?)$", 1)
+  }
+
+  // everything after the final slash, or the whole string if there is no slash
+  private string getBaseName(MethodCall renderCall) {
+    result = getTemplatePathValue(renderCall).regexpCapture("^/?(?:.*/)?([^/]*?)$", 1)
+  }
+
+  /**
+   * Gets the template file to be rendered by this render call, if any.
+   */
+  ErbFile getTemplateFile(MethodCall renderCall) {
+    result.getTemplateName() = getBaseName(renderCall) and
+    result.getRelativePath().matches("%app/views/" + getSubPath(renderCall) + "%")
+  }
+
+  /**
+   * Gets the local variables passed as context to the renderer.
+   */
+  HashLiteral getLocals(MethodCall renderCall) { result = renderCall.getKeywordArgument("locals") }
+}
 
 /**
  * Provides classes for working with Rails.
@@ -38,37 +75,15 @@ module Rails {
    * rendered content.
    */
   class RenderCall extends MethodCall instanceof RenderCallImpl {
-    private Expr getTemplatePathArgument() {
-      // TODO: support other ways of specifying paths (e.g. `file`)
-      result = [this.getKeywordArgument(["partial", "template", "action"]), this.getArgument(0)]
-    }
-
-    private string getTemplatePathValue() {
-      result = this.getTemplatePathArgument().getConstantValue().getStringlikeValue()
-    }
-
-    // everything up to and including the final slash, but ignoring any leading slash
-    private string getSubPath() {
-      result = this.getTemplatePathValue().regexpCapture("^/?(.*/)?(?:[^/]*?)$", 1)
-    }
-
-    // everything after the final slash, or the whole string if there is no slash
-    private string getBaseName() {
-      result = this.getTemplatePathValue().regexpCapture("^/?(?:.*/)?([^/]*?)$", 1)
-    }
-
     /**
      * Gets the template file to be rendered by this call, if any.
      */
-    ErbFile getTemplateFile() {
-      result.getTemplateName() = this.getBaseName() and
-      result.getRelativePath().matches("%app/views/" + this.getSubPath() + "%")
-    }
+    ErbFile getTemplateFile() { result = RenderCallUtils::getTemplateFile(this) }
 
     /**
-     * Get the local variables passed as context to the renderer
+     * Gets the local variables passed as context to the renderer.
      */
-    HashLiteral getLocals() { result = this.getKeywordArgument("locals") }
+    HashLiteral getLocals() { result = RenderCallUtils::getLocals(this) }
     // TODO: implicit renders in controller actions
   }
 
@@ -287,5 +302,92 @@ private class CookiesSameSiteProtectionSetting extends Settings::NillableStringl
     result = "Unsetting 'SameSite' can disable same-site cookie restrictions in some browsers."
   }
 }
+
 // TODO: initialization hooks, e.g. before_configuration, after_initialize...
 // TODO: initializers
+/** A synthetic global to represent the value passed to the `locals` argument of a render call for a specific ERB file. */
+private class LocalAssignsHashSyntheticGlobal extends SummaryComponent::SyntheticGlobal {
+  private ErbFile erbFile;
+  private string id;
+  // Note that we can't use an actual `Rails::RenderCall` here due to problems with non-monotonic recursion
+  private MethodCall renderCall;
+
+  LocalAssignsHashSyntheticGlobal() {
+    this = "LocalAssignsHashSyntheticGlobal+" + id and
+    id = erbFile.getRelativePath() + "+" + renderCall.getLocation() and
+    renderCall.getMethodName() = "render" and
+    RenderCallUtils::getTemplateFile(renderCall) = erbFile
+  }
+
+  /** Gets the `ErbFile` which this locals hash is accessible from. */
+  ErbFile getErbFile() { result = erbFile }
+
+  /** Gets the identifier for this particular locals hash synthetic global. */
+  string getId() { result = id }
+
+  /** Gets a call to render that can write to this hash. */
+  Rails::RenderCall getARenderCall() { result = renderCall }
+}
+
+/** A summary for `render` calls linked to some specific ERB file. */
+private class RenderLocalsSummary extends SummarizedCallable {
+  private LocalAssignsHashSyntheticGlobal glob;
+
+  RenderLocalsSummary() { this = "rails_render_locals()" + glob.getId() }
+
+  override Rails::RenderCall getACall() { result = glob.getARenderCall() }
+
+  override predicate propagatesFlowExt(string input, string output, boolean preservesValue) {
+    input = "Argument[locals:]" and
+    output = "SyntheticGlobal[" + glob + "]" and
+    preservesValue = true
+  }
+}
+
+/** A summary for calls to `local_assigns` in a view to access a `render` call `locals` hash. */
+private class AccessLocalsSummary extends SummarizedCallable {
+  private LocalAssignsHashSyntheticGlobal glob;
+
+  AccessLocalsSummary() { this = "rails_local_assigns()" + glob.getId() }
+
+  override MethodCall getACall() {
+    glob.getErbFile() = result.getLocation().getFile() and
+    result.getMethodName() = "local_assigns"
+  }
+
+  override predicate propagatesFlowExt(string input, string output, boolean preservesValue) {
+    input = "SyntheticGlobal[" + glob + "]" and
+    output = "ReturnValue" and
+    preservesValue = true
+  }
+}
+
+private string getAMethodNameFromErbFile(ErbFile f) {
+  result = any(MethodCall c | c.getLocation().getFile() = f).getMethodName()
+}
+
+private class AccessLocalsKeySummary extends SummarizedCallable {
+  private LocalAssignsHashSyntheticGlobal glob;
+  private string methodName;
+
+  AccessLocalsKeySummary() {
+    this = "rails_locals_key()" + glob.getId() + "#" + methodName and
+    methodName = getAMethodNameFromErbFile(glob.getErbFile()) and
+    // Limit method calls to those that could plausibly be a key in a `locals` hash argument
+    // TODO: this could be more precise but for problems using the dataflow library in this context
+    methodName =
+      any(HashLiteral l).getAKeyValuePair().getKey().getConstantValue().getStringlikeValue()
+  }
+
+  override MethodCall getACall() {
+    result.getLocation().getFile() = glob.getErbFile() and
+    result.getMethodName() = methodName and
+    result.getReceiver() instanceof SelfVariableReadAccess
+  }
+
+  override predicate propagatesFlowExt(string input, string output, boolean preservesValue) {
+    input = "SyntheticGlobal[" + glob + "].Element[:" + methodName + "]" and
+    output = "ReturnValue" and
+    preservesValue = true
+  }
+}

ruby/ql/lib/codeql/ruby/security/XSS.qll

@@ -162,46 +162,6 @@ private module Shared {
     erb = call.getLocation().getFile()
   }
 
-  /**
-   * Holds if some render call passes `value` for `hashKey` in the `locals`
-   * argument, in ERB file `erb`.
-   */
-  pragma[noinline]
-  private predicate renderCallLocals(string hashKey, Expr value, ErbFile erb) {
-    exists(Rails::RenderCall call, Pair kvPair |
-      call.getLocals().getAKeyValuePair() = kvPair and
-      kvPair.getValue() = value and
-      kvPair.getKey().getConstantValue().isStringlikeValue(hashKey) and
-      call.getTemplateFile() = erb
-    )
-  }
-
-  pragma[noinline]
-  private predicate isFlowFromLocals0(
-    CfgNodes::ExprNodes::ElementReferenceCfgNode refNode, string hashKey, ErbFile erb
-  ) {
-    exists(DataFlow::Node argNode |
-      argNode.asExpr() = refNode.getArgument(0) and
-      refNode.getReceiver().getExpr().(MethodCall).getMethodName() = "local_assigns" and
-      argNode.getALocalSource().getConstantValue().isStringlikeValue(hashKey) and
-      erb = refNode.getFile()
-    )
-  }
-
-  private predicate isFlowFromLocals(DataFlow::Node node1, DataFlow::Node node2) {
-    exists(string hashKey, ErbFile erb |
-      // node1 is a `locals` argument to a render call...
-      renderCallLocals(hashKey, node1.asExpr().getExpr(), erb)
-    |
-      // node2 is an element reference against `local_assigns`
-      isFlowFromLocals0(node2.asExpr(), hashKey, erb)
-      or
-      // ...node2 is a "method call" to a "method" with `hashKey` as its name
-      // TODO: This may be a variable read in reality that we interpret as a method call
-      isMethodCall(node2.asExpr().getExpr(), hashKey, erb)
-    )
-  }
-
   /**
    * Holds if `action` contains an assignment of `value` to an instance
    * variable named `name`, in ERB file `erb`.
@@ -275,8 +235,6 @@ private module Shared {
    * An additional step that is preserves dataflow in the context of XSS.
    */
   predicate isAdditionalXssFlowStep(DataFlow::Node node1, DataFlow::Node node2) {
-    isFlowFromLocals(node1, node2)
-    or
     isFlowFromControllerInstanceVariable(node1, node2)
     or
     isFlowIntoHelperMethod(node1, node2)