start modelling some file access concepts

ql/lib/codeql/ruby/Concepts.qll

@@ -36,6 +36,46 @@ module SqlExecution {
   }
 }
 
+/**
+ * A data flow node that performs a file system access (read, write, copy, permissions, stats, etc).
+ */
+abstract class FileSystemAccess extends DataFlow::Node {
+  /** Gets an argument to this file system access that is interpreted as a path. */
+  abstract DataFlow::Node getAPathArgument();
+
+  /**
+   * Gets an argument to this file system access that is interpreted as a root folder
+   * in which the path arguments are constrained.
+   *
+   * In other words, if a root argument is provided, the underlying file access does its own
+   * sanitization to prevent the path arguments from traversing outside the root folder.
+   */
+  DataFlow::Node getRootPathArgument() { none() }
+
+  /**
+   * Holds if this file system access will reject paths containing upward navigation
+   * segments (`../`).
+   *
+   * `argument` should refer to the relevant path argument or root path argument.
+   */
+  predicate isUpwardNavigationRejected(DataFlow::Node argument) { none() }
+}
+
+/**
+ * A data flow node that reads data from the file system.
+ */
+abstract class FileSystemReadAccess extends FileSystemAccess {
+  /** Gets a node that represents data from the file system. */
+  abstract DataFlow::Node getADataNode();
+}
+
+
+/**
+ * A data flow node that contains a file name or an array of file names from the local file system.
+ */
+abstract class FileNameSource extends DataFlow::Node { }
+
+
 /**
  * A data-flow node that escapes meta-characters, which could be used to prevent
  * injection attacks.

ql/lib/codeql/ruby/Frameworks.qll

@@ -6,3 +6,4 @@ private import codeql.ruby.frameworks.ActionController
 private import codeql.ruby.frameworks.ActiveRecord
 private import codeql.ruby.frameworks.ActionView
 private import codeql.ruby.frameworks.StandardLibrary
+private import codeql.ruby.frameworks.Files

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

@@ -0,0 +1,54 @@
+/**
+ * Provides classes for working with file system libraries.
+ */
+
+private import ruby
+private import codeql.ruby.Concepts
+private import codeql.ruby.ApiGraphs
+
+/** A permissions argument of a call to a File/FileUtils method that may modify file permissions */
+/*
+class PermissionArgument extends DataFlow::Node {
+  private DataFlow::CallNode call;
+
+  PermissionArgument() {
+    exists(string methodName |
+      call = API::getTopLevelMember(["File", "FileUtils"]).getAMethodCall(methodName)
+    |
+      methodName in ["chmod", "chmod_R", "lchmod"] and this = call.getArgument(0)
+      or
+      methodName = "mkfifo" and this = call.getArgument(1)
+      or
+      methodName in ["new", "open"] and this = call.getArgument(2)
+      or
+      methodName in ["install", "makedirs", "mkdir", "mkdir_p", "mkpath"] and
+      this = call.getKeywordArgument("mode")
+      // TODO: defaults for optional args? This may depend on the umask
+    )
+  }
+
+  MethodCall getCall() { result = call.asExpr().getExpr() }
+}
+*/
+
+
+class StdLibFileNameSource extends FileNameSource {
+  StdLibFileNameSource() {
+    this = API::getTopLevelMember("File").getAMethodCall(["join", "path", "to_path", "readlink"])
+
+  }
+}
+
+/**
+ * Classes and predicates for modelling the `File` module from the standard
+ * library.
+ */
+private module File {
+
+  class FileModuleReader extends FileSystemReadAccess, DataFlow::CallNode {
+    FileModuleReader() {
+      this = API::getTopLevelMember("File").getAMethodCall(["new", "open"])
+    }
+  }
+
+}