Merge pull request github#3273 from Semmle/rdmarsh/cpp/RemoteFlowSource-model

C++: Add remote flow sources via models

Author: jbj

cpp/ql/src/semmle/code/cpp/models/implementations/Fread.qll

@@ -1,6 +1,7 @@
 import semmle.code.cpp.models.interfaces.Alias
+import semmle.code.cpp.models.interfaces.FlowSource
 
-class Fread extends AliasFunction {
+class Fread extends AliasFunction, RemoteFlowFunction {
   Fread() { this.hasGlobalName("fread") }
 
   override predicate parameterNeverEscapes(int n) {
@@ -11,4 +12,9 @@ class Fread extends AliasFunction {
   override predicate parameterEscapesOnlyViaReturn(int n) { none() }
 
   override predicate parameterIsAlwaysReturned(int n) { none() }
+
+  override predicate hasRemoteFlowSource(FunctionOutput output, string description) {
+    output.isParameterDeref(0) and
+    description = "String read by " + this.getName()
+  }
 }

cpp/ql/src/semmle/code/cpp/models/implementations/Gets.qll

@@ -3,12 +3,13 @@ import semmle.code.cpp.models.interfaces.Taint
 import semmle.code.cpp.models.interfaces.ArrayFunction
 import semmle.code.cpp.models.interfaces.Alias
 import semmle.code.cpp.models.interfaces.SideEffect
+import semmle.code.cpp.models.interfaces.FlowSource
 
 /**
  * The standard functions `gets` and `fgets`.
  */
 class GetsFunction extends DataFlowFunction, TaintFunction, ArrayFunction, AliasFunction,
-  SideEffectFunction {
+  SideEffectFunction, RemoteFlowFunction {
   GetsFunction() {
     exists(string name | hasGlobalOrStdName(name) |
       name = "gets" or // gets(str)
@@ -42,4 +43,9 @@ class GetsFunction extends DataFlowFunction, TaintFunction, ArrayFunction, Alias
     buffer = true and
     mustWrite = true
   }
+
+  override predicate hasRemoteFlowSource(FunctionOutput output, string description) {
+    output.isParameterDeref(0) and
+    description = "String read by " + this.getName()
+  }
 }

cpp/ql/src/semmle/code/cpp/models/interfaces/FlowSource.qll

@@ -0,0 +1,21 @@
+/**
+ * Provides a class for modeling functions that return data from potentially untrusted sources. To use
+ * this QL library, create a QL class extending `DataFlowFunction` with a
+ * characteristic predicate that selects the function or set of functions you
+ * are modeling. Within that class, override the predicates provided by
+ * `RemoteFlowFunction` to match the flow within that function.
+ */
+
+import cpp
+import FunctionInputsAndOutputs
+import semmle.code.cpp.models.Models
+
+/**
+ * A library function which returns data read from a network connection.
+ */
+abstract class RemoteFlowFunction extends Function {
+  /**
+   * Holds if remote data described by `description` flows from `output` of a call to this function.
+   */
+  abstract predicate hasRemoteFlowSource(FunctionOutput output, string description);
+}

cpp/ql/src/semmle/code/cpp/security/FlowSources.qll

@@ -0,0 +1,44 @@
+/**
+ * Provides classes representing various flow sources for taint tracking.
+ */
+
+import cpp
+import semmle.code.cpp.ir.dataflow.DataFlow
+private import semmle.code.cpp.ir.IR
+import semmle.code.cpp.models.interfaces.FlowSource
+
+/** A data flow source of remote user input. */
+abstract class RemoteFlowSource extends DataFlow::Node {
+  /** Gets a string that describes the type of this remote flow source. */
+  abstract string getSourceType();
+}
+
+private class TaintedReturnSource extends RemoteFlowSource {
+  string sourceType;
+
+  TaintedReturnSource() {
+    exists(RemoteFlowFunction func, CallInstruction instr, FunctionOutput output |
+      asInstruction() = instr and
+      instr.getStaticCallTarget() = func and
+      func.hasRemoteFlowSource(output, sourceType) and
+      output.isReturnValue()
+    )
+  }
+
+  override string getSourceType() { result = sourceType }
+}
+
+private class TaintedParameterSource extends RemoteFlowSource {
+  string sourceType;
+
+  TaintedParameterSource() {
+    exists(RemoteFlowFunction func, WriteSideEffectInstruction instr, FunctionOutput output |
+      asInstruction() = instr and
+      instr.getPrimaryInstruction().(CallInstruction).getStaticCallTarget() = func and
+      func.hasRemoteFlowSource(output, sourceType) and
+      output.isParameterDeref(instr.getIndex())
+    )
+  }
+
+  override string getSourceType() { result = sourceType }
+}