Merge pull request github#6092 from RasmusWL/markupsafe-modeling

Python: Add `MarkupSafe` model

Author: tausbn

docs/codeql/support/reusables/frameworks.rst

@@ -178,3 +178,4 @@ Python built-in support
    pycryptodome, Cryptography library
    pycryptodomex, Cryptography library
    rsa, Cryptography library
+   MarkupSafe, Escaping Library

python/change-notes/2021-06-16-MarkupSafe-add-modeling.md

@@ -0,0 +1,2 @@
+lgtm,codescanning
+* Added modeling of the PyPI package `MarkupSafe`.

python/ql/src/semmle/python/Concepts.qll

@@ -293,6 +293,78 @@ module SqlExecution {
   }
 }
 
+/**
+ * A data-flow node that escapes meta-characters, which could be used to prevent
+ * injection attacks.
+ *
+ * Extend this class to refine existing API models. If you want to model new APIs,
+ * extend `Escaping::Range` instead.
+ */
+class Escaping extends DataFlow::Node {
+  Escaping::Range range;
+
+  Escaping() {
+    this = range and
+    // escapes that don't have _both_ input/output defined are not valid
+    exists(range.getAnInput()) and
+    exists(range.getOutput())
+  }
+
+  /** Gets an input that will be escaped. */
+  DataFlow::Node getAnInput() { result = range.getAnInput() }
+
+  /** Gets the output that contains the escaped data. */
+  DataFlow::Node getOutput() { result = range.getOutput() }
+
+  /**
+   * Gets the context that this function escapes for, such as `html`, or `url`.
+   */
+  string getKind() { result = range.getKind() }
+}
+
+/** Provides a class for modeling new escaping APIs. */
+module Escaping {
+  /**
+   * A data-flow node that escapes meta-characters, which could be used to prevent
+   * injection attacks.
+   *
+   * Extend this class to model new APIs. If you want to refine existing API models,
+   * extend `Escaping` instead.
+   */
+  abstract class Range extends DataFlow::Node {
+    /** Gets an input that will be escaped. */
+    abstract DataFlow::Node getAnInput();
+
+    /** Gets the output that contains the escaped data. */
+    abstract DataFlow::Node getOutput();
+
+    /**
+     * Gets the context that this function escapes for.
+     *
+     * While kinds are represented as strings, this should not be relied upon. Use the
+     * predicates in  the `Escaping` module, such as `getHtmlKind`.
+     */
+    abstract string getKind();
+  }
+
+  /** Gets the escape-kind for escaping a string so it can safely be included in HTML. */
+  string getHtmlKind() { result = "html" }
+  // TODO: If adding an XML kind, update the modeling of the `MarkupSafe` PyPI package.
+  //
+  // Technically it claims to escape for both HTML and XML, but for now we don't have
+  // anything that relies on XML escaping, so I'm going to defer deciding whether they
+  // should be the same kind, or whether they deserve to be treated differently.
+}
+
+/**
+ * An escape of a string so it can be safely included in
+ * the body of an HTML element, for example, replacing `{}` in
+ * `<p>{}</p>`.
+ */
+class HtmlEscaping extends Escaping {
+  HtmlEscaping() { range.getKind() = Escaping::getHtmlKind() }
+}
+
 /** Provides classes for modeling HTTP-related APIs. */
 module HTTP {
   import semmle.python.web.HttpConstants

python/ql/src/semmle/python/Frameworks.qll

@@ -16,6 +16,7 @@ private import semmle.python.frameworks.Flask
 private import semmle.python.frameworks.Idna
 private import semmle.python.frameworks.Invoke
 private import semmle.python.frameworks.Jmespath
+private import semmle.python.frameworks.MarkupSafe
 private import semmle.python.frameworks.Multidict
 private import semmle.python.frameworks.Mysql
 private import semmle.python.frameworks.MySQLdb

python/ql/src/semmle/python/frameworks/MarkupSafe.qll

@@ -0,0 +1,151 @@
+/**
+ * Provides classes modeling security-relevant aspects of the `MarkupSafe` PyPI package.
+ * See https://markupsafe.palletsprojects.com/en/2.0.x/.
+ */
+
+private import python
+private import semmle.python.dataflow.new.DataFlow
+private import semmle.python.dataflow.new.TaintTracking
+private import semmle.python.Concepts
+private import semmle.python.ApiGraphs
+
+/**
+ * Provides models for the `MarkupSafe` PyPI package.
+ * See https://markupsafe.palletsprojects.com/en/2.0.x/.
+ */
+private module MarkupSafeModel {
+  /**
+   * Provides models for the `markupsafe.Markup` class
+   *
+   * See https://markupsafe.palletsprojects.com/en/2.0.x/escaping/#markupsafe.Markup.
+   */
+  module Markup {
+    /** Gets a reference to the `markupsafe.Markup` class. */
+    API::Node classRef() {
+      result = API::moduleImport("markupsafe").getMember("Markup")
+      or
+      result = API::moduleImport("flask").getMember("Markup")
+    }
+
+    /**
+     * A source of instances of `markupsafe.Markup`, extend this class to model new instances.
+     *
+     * This can include instantiations of the class, return values from function
+     * calls, or a special parameter that will be set when functions are called by an external
+     * library.
+     *
+     * Use the predicate `Markup::instance()` to get references to instances of `markupsafe.Markup`.
+     */
+    abstract class InstanceSource extends DataFlow::LocalSourceNode { }
+
+    /** A direct instantiation of `markupsafe.Markup`. */
+    private class ClassInstantiation extends InstanceSource, DataFlow::CallCfgNode {
+      override CallNode node;
+
+      ClassInstantiation() { this = classRef().getACall() }
+    }
+
+    /** Gets a reference to an instance of `markupsafe.Markup`. */
+    private DataFlow::LocalSourceNode instance(DataFlow::TypeTracker t) {
+      t.start() and
+      result instanceof InstanceSource
+      or
+      exists(DataFlow::TypeTracker t2 | result = instance(t2).track(t2, t))
+    }
+
+    /** Gets a reference to an instance of `markupsafe.Markup`. */
+    DataFlow::Node instance() { instance(DataFlow::TypeTracker::end()).flowsTo(result) }
+
+    /** A string concatenation with a `markupsafe.Markup` involved. */
+    class StringConcat extends Markup::InstanceSource, DataFlow::CfgNode {
+      override BinaryExprNode node;
+
+      StringConcat() {
+        node.getOp() instanceof Add and
+        instance().asCfgNode() in [node.getLeft(), node.getRight()]
+      }
+    }
+
+    /** A string format with `markupsafe.Markup` as the format string. */
+    class StringFormat extends Markup::InstanceSource, DataFlow::MethodCallNode {
+      StringFormat() { this.calls(instance(), "format") }
+    }
+
+    /** A %-style string format with `markupsafe.Markup` as the format string. */
+    class PercentStringFormat extends Markup::InstanceSource, DataFlow::CfgNode {
+      override BinaryExprNode node;
+
+      PercentStringFormat() {
+        node.getOp() instanceof Mod and
+        instance().asCfgNode() = node.getLeft()
+      }
+    }
+
+    /** Taint propagation for `markupsafe.Markup`. */
+    class AddtionalTaintSteps extends TaintTracking::AdditionalTaintStep {
+      override predicate step(DataFlow::Node nodeFrom, DataFlow::Node nodeTo) {
+        nodeTo.(ClassInstantiation).getArg(0) = nodeFrom
+      }
+    }
+  }
+
+  /** Any escaping performed via the `markupsafe` package. */
+  abstract private class MarkupSafeEscape extends Escaping::Range {
+    override string getKind() {
+      // TODO: this package claims to escape for both HTML and XML, but for now we don't
+      // model XML.
+      result = Escaping::getHtmlKind()
+    }
+  }
+
+  /** A call to any of the escaping functions in `markupsafe` */
+  private class MarkupSafeEscapeCall extends Markup::InstanceSource, MarkupSafeEscape,
+    DataFlow::CallCfgNode {
+    MarkupSafeEscapeCall() {
+      this = API::moduleImport("markupsafe").getMember(["escape", "escape_silent"]).getACall()
+      or
+      this = Markup::classRef().getMember("escape").getACall()
+      or
+      this = API::moduleImport("flask").getMember("escape").getACall()
+    }
+
+    override DataFlow::Node getAnInput() { result = this.getArg(0) }
+
+    override DataFlow::Node getOutput() { result = this }
+  }
+
+  /**
+   * An escape from string concatenation with a `markupsafe.Markup` involved.
+   *
+   * Only things that are not already a `markupsafe.Markup` instances will be escaped.
+   */
+  private class MarkupEscapeFromStringConcat extends MarkupSafeEscape, Markup::StringConcat {
+    override DataFlow::Node getAnInput() {
+      result.asCfgNode() in [node.getLeft(), node.getRight()] and
+      not result = Markup::instance()
+    }
+
+    override DataFlow::Node getOutput() { result = this }
+  }
+
+  /** A escape from string format with `markupsafe.Markup` as the format string. */
+  private class MarkupEscapeFromStringFormat extends MarkupSafeEscape, Markup::StringFormat {
+    override DataFlow::Node getAnInput() {
+      result in [this.getArg(_), this.getArgByName(_)] and
+      not result = Markup::instance()
+    }
+
+    override DataFlow::Node getOutput() { result = this }
+  }
+
+  /** A escape from %-style string format with `markupsafe.Markup` as the format string. */
+  private class MarkupEscapeFromPercentStringFormat extends MarkupSafeEscape,
+    Markup::PercentStringFormat {
+    override DataFlow::Node getAnInput() {
+      result.asCfgNode() = node.getRight() and
+      not result = Markup::instance()
+    }
+
+    override DataFlow::Node getOutput() { result = this }
+  }
+}

python/ql/src/semmle/python/security/dataflow/ReflectedXSS.qll

@@ -29,4 +29,13 @@ class ReflectedXssConfiguration extends TaintTracking::Configuration {
   override predicate isSanitizerGuard(DataFlow::BarrierGuard guard) {
     guard instanceof StringConstCompare
   }
+
+  // TODO: For now, since there is not an `isSanitizingStep` member-predicate part of a
+  // `TaintTracking::Configuration`, we use treat the output is a taint-sanitizer. This
+  // is slightly imprecise, which you can see in the `m_unsafe + SAFE` test-case in
+  // python/ql/test/library-tests/frameworks/markupsafe/taint_test.py
+  //
+  // However, it is better than `getAnInput()`. Due to use-use flow, that would remove
+  // the taint-flow to `SINK()` in `some_escape(tainted); SINK(tainted)`.
+  override predicate isSanitizer(DataFlow::Node node) { node = any(HtmlEscaping esc).getOutput() }
 }

python/ql/test/experimental/meta/ConceptsTest.qll

@@ -129,6 +129,38 @@ class SqlExecutionTest extends InlineExpectationsTest {
   }
 }
 
+class EscapingTest extends InlineExpectationsTest {
+  EscapingTest() { this = "EscapingTest" }
+
+  override string getARelevantTag() { result in ["escapeInput", "escapeOutput", "escapeKind"] }
+
+  override predicate hasActualResult(Location location, string element, string tag, string value) {
+    exists(location.getFile().getRelativePath()) and
+    exists(Escaping esc |
+      exists(DataFlow::Node data |
+        location = data.getLocation() and
+        element = data.toString() and
+        value = prettyNodeForInlineTest(data) and
+        (
+          data = esc.getAnInput() and
+          tag = "escapeInput"
+          or
+          data = esc.getOutput() and
+          tag = "escapeOutput"
+        )
+      )
+      or
+      exists(string format |
+        location = esc.getLocation() and
+        element = format and
+        value = format and
+        format = esc.getKind() and
+        tag = "escapeKind"
+      )
+    )
+  }
+}
+
 class HttpServerRouteSetupTest extends InlineExpectationsTest {
   HttpServerRouteSetupTest() { this = "HttpServerRouteSetupTest" }
 

python/ql/test/library-tests/frameworks/markupsafe/ConceptsTest.expected

@@ -0,0 +1,2 @@
+import python
+import experimental.meta.ConceptsTest

python/ql/test/library-tests/frameworks/markupsafe/ConceptsTest.ql

@@ -0,0 +1,3 @@
+argumentToEnsureNotTaintedNotMarkedAsSpurious
+untaintedArgumentToEnsureTaintedNotMarkedAsMissing
+failures