Docs: add path query example to data flow docs

docs/codeql/codeql-language-guides/analyzing-data-flow-in-cpp.rst

@@ -314,7 +314,7 @@ Exercise 2: Write a query that finds all hard-coded strings used to create a ``h
 
 Exercise 3: Write a class that represents flow sources from ``getenv``. (`Answer <#exercise-3>`__)
 
-Exercise 4: Using the answers from 2 and 3, write a query which finds all global data flow paths from ``getenv`` to ``gethostbyname``. (`Answer <#exercise-4>`__)
+Exercise 4: Using the answers from 2 and 3, write a query which finds all global data flow paths from ``getenv`` to ``gethostbyname``. (`Answer <#exercise-4>`__ `Answer as a path query <#path-query-example>`__)
 
 Answers
 -------
@@ -411,6 +411,48 @@ Exercise 4
      GetenvToGethostbynameFlow::flow(source, sink)
    select getenv, fc
 
+Path query example
+~~~~~~~~~~~~~~~~~~
+
+Here is the answer to exercise 4 above, converted into a path query:
+
+.. code-block:: ql
+
+   /**
+    * @kind path-problem
+    * @problem.severity warning
+    * @id getenv-to-gethostbyname
+    */
+
+   import cpp
+   import semmle.code.cpp.dataflow.new.DataFlow
+
+   class GetenvSource extends DataFlow::Node {
+     GetenvSource() { this.asIndirectExpr(1).(FunctionCall).getTarget().hasGlobalName("getenv") }
+   }
+
+   module GetenvToGethostbynameConfiguration implements DataFlow::ConfigSig {
+     predicate isSource(DataFlow::Node source) { source instanceof GetenvSource }
+
+     predicate isSink(DataFlow::Node sink) {
+       exists(FunctionCall fc |
+         sink.asIndirectExpr(1) = fc.getArgument(0) and
+         fc.getTarget().hasName("gethostbyname")
+       )
+     }
+   }
+
+   module GetenvToGethostbynameFlow = DataFlow::Global<GetenvToGethostbynameConfiguration>;
+
+   import GetenvToGethostbynameFlow::PathGraph
+
+   from GetenvToGethostbynameFlow::PathNode source, GetenvToGethostbynameFlow::PathNode sink
+   where GetenvToGethostbynameFlow::flowPath(source, sink)
+   select sink.getNode(), source, sink, "This file access uses data from $@.",
+     source, "user-controllable input."
+
+For more information, see "`Creating path queries <https://codeql.github.com/docs/writing-codeql-queries/creating-path-queries/>`__".
+
 Further reading
 ---------------
 

docs/codeql/codeql-language-guides/analyzing-data-flow-in-csharp.rst

@@ -287,7 +287,7 @@ Exercise 2: Find all hard-coded strings passed to ``System.Uri``, using global d
 
 Exercise 3: Define a class that represents flow sources from ``System.Environment.GetEnvironmentVariable``. (`Answer <#exercise-3>`__)
 
-Exercise 4: Using the answers from 2 and 3, write a query which finds all global data flow paths from ``System.Environment.GetEnvironmentVariable`` to ``System.Uri``. (`Answer <#exercise-4>`__)
+Exercise 4: Using the answers from 2 and 3, write a query which finds all global data flow paths from ``System.Environment.GetEnvironmentVariable`` to ``System.Uri``. (`Answer <#exercise-4>`__ `Answer as a path query <#path-query-example>`__)
 
 Extending library data flow
 ---------------------------
@@ -537,6 +537,48 @@ This can be adapted from the ``SystemUriFlow`` class:
      }
    }
 
+Path query example
+~~~~~~~~~~~~~~~~~~
+
+Here is the answer to exercise 4 above, converted into a path query:
+
+.. code-block:: ql
+
+   /**
+    * @kind path-problem
+    * @problem.severity warning
+    * @id getenv-to-gethostbyname
+    */
+
+   import csharp
+
+   class EnvironmentVariableFlowSource extends DataFlow::ExprNode {
+     EnvironmentVariableFlowSource() {
+       this.getExpr().(MethodCall).getTarget().hasQualifiedName("System.Environment.GetEnvironmentVariable")
+     }
+   }
+
+   module EnvironmentToUriConfig implements DataFlow::ConfigSig {
+     predicate isSource(DataFlow::Node src) {
+       src instanceof EnvironmentVariableFlowSource
+     }
+
+     predicate isSink(DataFlow::Node sink) {
+       exists(Call c | c.getTarget().(Constructor).getDeclaringType().hasQualifiedName("System.Uri")
+       and sink.asExpr()=c.getArgument(0))
+     }
+   }
+
+   module EnvironmentToUriFlow = DataFlow::Global<EnvironmentToUriConfig>;
+
+   import EnvironmentToUriFlow::PathGraph
+
+   from EnvironmentToUriFlow::PathNode src, EnvironmentToUriFlow::PathNode sink
+   where EnvironmentToUriFlow::flowPath(src, sink)
+   select src.getNode(), src, sink, "This environment variable constructs a 'System.Uri' $@.", sink, "here"
+
+For more information, see "`Creating path queries <https://codeql.github.com/docs/writing-codeql-queries/creating-path-queries/>`__".
+
 Further reading
 ---------------
 

docs/codeql/codeql-language-guides/analyzing-data-flow-in-go.rst

@@ -224,7 +224,7 @@ The resulting module has an identical signature to the one obtained from ``DataF
 Flow sources
 ~~~~~~~~~~~~
 
-The data flow library contains some predefined flow sources. The class ``RemoteFlowSource`` (defined in ``semmle.code.java.dataflow.FlowSources``) represents data flow sources that may be controlled by a remote user, which is useful for finding security problems.
+The data flow library contains some predefined flow sources. The class ``RemoteFlowSource`` represents data flow sources that may be controlled by a remote user, which is useful for finding security problems.
 
 Examples
 ~~~~~~~~
@@ -252,7 +252,7 @@ Exercise 2: Write a query that finds all hard-coded strings used to create a ``u
 
 Exercise 3: Write a class that represents flow sources from ``os.Getenv(..)``. (`Answer <#exercise-3>`__)
 
-Exercise 4: Using the answers from 2 and 3, write a query which finds all global data flow paths from ``os.Getenv`` to ``url.URL``. (`Answer <#exercise-4>`__)
+Exercise 4: Using the answers from 2 and 3, write a query which finds all global data flow paths from ``os.Getenv`` to ``url.URL``. (`Answer <#exercise-4>`__ `Answer as a path query <#path-query-example>`__)
 
 Answers
 -------
@@ -312,7 +312,7 @@ Exercise 3
 
    import go
 
-   class GetenvSource extends CallExpr {
+   class GetenvSource extends DataFlow::CallNode {
      GetenvSource() {
        exists(Function m | m = this.getTarget() |
          m.hasQualifiedName("os", "Getenv")
@@ -327,7 +327,7 @@ Exercise 4
 
    import go
 
-   class GetenvSource extends CallExpr {
+   class GetenvSource extends DataFlow::CallNode {
      GetenvSource() {
        exists(Function m | m = this.getTarget() |
          m.hasQualifiedName("os", "Getenv")
@@ -350,7 +350,6 @@ Exercise 4
          sink.asExpr() = call.getArgument(0)
        )
      }
-     }
    }
 
    module GetenvToURLFlow = DataFlow::Global<GetenvToURLConfig>;
@@ -359,6 +358,56 @@ Exercise 4
    where GetenvToURLFlow::flow(src, sink)
    select src, "This environment variable constructs a URL $@.", sink, "here"
 
+Path query example
+~~~~~~~~~~~~~~~~~~
+
+Here is the answer to exercise 4 above, converted into a path query:
+
+.. code-block:: ql
+
+   /**
+    * @kind path-problem
+    * @problem.severity warning
+    * @id getenv-to-url
+    */
+
+   import go
+
+   class GetenvSource extends DataFlow::CallNode {
+     GetenvSource() {
+       exists(Function m | m = this.getTarget() |
+         m.hasQualifiedName("os", "Getenv")
+       )
+     }
+   }
+
+   module GetenvToURLConfig implements DataFlow::ConfigSig {
+     predicate isSource(DataFlow::Node source) {
+       source instanceof GetenvSource
+     }
+
+     predicate isSink(DataFlow::Node sink) {
+       exists(Function urlParse, CallExpr call |
+         (
+           urlParse.hasQualifiedName("url", "Parse") or
+           urlParse.hasQualifiedName("url", "ParseRequestURI")
+         ) and
+         call.getTarget() = urlParse and
+         sink.asExpr() = call.getArgument(0)
+       )
+     }
+   }
+
+   module GetenvToURLFlow = DataFlow::Global<GetenvToURLConfig>;
+
+   import GetenvToURLFlow::PathGraph
+
+   from GetenvToURLFlow::PathNode src, GetenvToURLFlow::PathNode sink
+   where GetenvToURLFlow::flowPath(src, sink)
+   select src.getNode(), src, sink, "This environment variable constructs a URL $@.", sink, "here"
+
+For more information, see "`Creating path queries <https://codeql.github.com/docs/writing-codeql-queries/creating-path-queries/>`__".
+
 Further reading
 ---------------
 

docs/codeql/codeql-language-guides/analyzing-data-flow-in-java.rst

@@ -262,7 +262,7 @@ Exercise 2: Write a query that finds all hard-coded strings used to create a ``j
 
 Exercise 3: Write a class that represents flow sources from ``java.lang.System.getenv(..)``. (`Answer <#exercise-3>`__)
 
-Exercise 4: Using the answers from 2 and 3, write a query which finds all global data flow paths from ``getenv`` to ``java.net.URL``. (`Answer <#exercise-4>`__)
+Exercise 4: Using the answers from 2 and 3, write a query which finds all global data flow paths from ``getenv`` to ``java.net.URL``. (`Answer <#exercise-4>`__ `Answer as a path query <#path-query-example>`__)
 
 Answers
 -------
@@ -361,6 +361,54 @@ Exercise 4
    where GetenvToURLFlow::flow(src, sink)
    select src, "This environment variable constructs a URL $@.", sink, "here"
 
+Path query example
+~~~~~~~~~~~~~~~~~~
+
+Here is the answer to exercise 4 above, converted into a path query:
+
+.. code-block:: ql
+
+   /**
+    * @kind path-problem
+    * @problem.severity warning
+    * @id getenv-to-url
+    */
+
+   import java
+   import semmle.code.java.dataflow.DataFlow
+
+   class GetenvSource extends DataFlow::ExprNode {
+     GetenvSource() {
+       exists(Method m | m = this.asExpr().(MethodCall).getMethod() |
+         m.hasName("getenv") and
+         m.getDeclaringType() instanceof TypeSystem
+       )
+     }
+   }
+
+   module GetenvToURLConfig implements DataFlow::ConfigSig {
+     predicate isSource(DataFlow::Node source) {
+       source instanceof GetenvSource
+     }
+
+     predicate isSink(DataFlow::Node sink) {
+       exists(Call call |
+         sink.asExpr() = call.getArgument(0) and
+         call.getCallee().(Constructor).getDeclaringType().hasQualifiedName("java.net", "URL")
+       )
+     }
+   }
+
+   module GetenvToURLFlow = DataFlow::Global<GetenvToURLConfig>;
+
+   import GetenvToURLFlow::PathGraph
+
+   from GetenvToURLFlow::PathNode src, GetenvToURLFlow::PathNode sink
+   where GetenvToURLFlow::flowPath(src, sink)
+   select src.getNode(), src, sink, "This environment variable constructs a URL $@.", sink, "here"
+
+For more information, see "`Creating path queries <https://codeql.github.com/docs/writing-codeql-queries/creating-path-queries/>`__".
+
 Further reading
 ---------------
 

docs/codeql/codeql-language-guides/analyzing-data-flow-in-javascript-and-typescript.rst

@@ -456,7 +456,7 @@ Exercise 3: Write a class which represents flow sources from the array elements
 Hint: array indices are properties with numeric names; you can use regular expression matching to check this. (`Answer <#exercise-3>`__)
 
 Exercise 4: Using the answers from 2 and 3, write a query which finds all global data flow paths from array elements of the result of a call to the ``tagName`` argument to the
-``createElement`` function. (`Answer <#exercise-4>`__)
+``createElement`` function. (`Answer <#exercise-4>`__ `Answer as a path query <#path-query-example>`__)
 
 Answers
 -------
@@ -541,6 +541,48 @@ Exercise 4
   where HardCodedTagNameFlow::flow(source, sink)
   select source, sink
 
+Path query example
+~~~~~~~~~~~~~~~~~~
+
+Here is the answer to exercise 4 above, converted into a path query:
+
+.. code-block:: ql
+
+  /**
+   * @kind path-problem
+   * @problem.severity warning
+   * @id hard-coded-tag-name
+   */
+
+  import javascript
+
+  class ArrayEntryCallResult extends DataFlow::Node {
+    ArrayEntryCallResult() {
+      exists(DataFlow::CallNode call, string index |
+        this = call.getAPropertyRead(index) and
+        index.regexpMatch("\\d+")
+      )
+    }
+  }
+
+  module HardCodedTagNameConfig implements DataFlow::ConfigSig {
+    predicate isSource(DataFlow::Node source) { source instanceof ArrayEntryCallResult }
+
+    predicate isSink(DataFlow::Node sink) {
+      sink = DataFlow::globalVarRef("document").getAMethodCall("createElement").getArgument(0)
+    }
+  }
+
+  module HardCodedTagNameFlow = DataFlow::Global<HardCodedTagNameConfig>;
+
+   import HardCodedTagNameFlow::PathGraph
+
+   from HardCodedTagNameFlow::PathNode source, HardCodedTagNameFlow::PathNode sink
+   where HardCodedTagNameFlow::flowPath(source, sink)
+   select sink.getNode(), source, sink, "Hard-coded tag name $@.", source, "here"
+
+For more information, see "`Creating path queries <https://codeql.github.com/docs/writing-codeql-queries/creating-path-queries/>`__".
+
 Further reading
 ---------------
 

docs/codeql/codeql-language-guides/analyzing-data-flow-in-python.rst

@@ -354,11 +354,50 @@ This data flow configuration tracks data flow from environment variables to open
     select fileOpen, "This call to 'os.open' uses data from $@.",
       environment, "call to 'os.getenv'"
 
+Path query example
+~~~~~~~~~~~~~~~~~~
+
+Here is the network input example above, converted into a path query:
+
+.. code-block:: ql
+
+    /**
+     * @kind path-problem
+     * @problem.severity warning
+     * @id file-system-access-from-remote-input
+     */
+
+    import python
+    import semmle.python.dataflow.new.DataFlow
+    import semmle.python.dataflow.new.TaintTracking
+    import semmle.python.dataflow.new.RemoteFlowSources
+    import semmle.python.Concepts
+
+    module RemoteToFileConfiguration implements DataFlow::ConfigSig {
+      predicate isSource(DataFlow::Node source) {
+        source instanceof RemoteFlowSource
+      }
+
+      predicate isSink(DataFlow::Node sink) {
+        sink = any(FileSystemAccess fa).getAPathArgument()
+      }
+    }
+
+    module RemoteToFileFlow = TaintTracking::Global<RemoteToFileConfiguration>;
+
+    import RemoteToFileFlow::PathGraph
+
+    from RemoteToFileFlow::PathNode input, RemoteToFileFlow::PathNode fileAccess
+    where RemoteToFileFlow::flowPath(input, fileAccess)
+    select fileAccess.getNode(), input, fileAccess, "This file access uses data from $@.",
+      input, "user-controllable input."
+
+For more information, see "`Creating path queries <https://codeql.github.com/docs/writing-codeql-queries/creating-path-queries/>`__".
 
 Further reading
 ---------------
 
-- `Exploring data flow with path queries  <https://docs.github.com/en/code-security/codeql-for-vs-code/getting-started-with-codeql-for-vs-code/exploring-data-flow-with-path-queries>`__ in the GitHub documentation.
+- `Creating path queries  <https://codeql.github.com/docs/writing-codeql-queries/creating-path-queries/>`__.
 
 
 .. include:: ../reusables/python-further-reading.rst