C++: Block summary flow through strdup and friends

cpp/ql/lib/semmle/code/cpp/ir/dataflow/internal/DataFlowPrivate.qll

@@ -7,6 +7,9 @@ private import SsaInternals as Ssa
 private import DataFlowImplCommon as DataFlowImplCommon
 private import codeql.util.Unit
 private import Node0ToString
+private import ModelUtil
+private import semmle.code.cpp.models.interfaces.FunctionInputsAndOutputs as IO
+private import semmle.code.cpp.models.interfaces.DataFlow as DF
 
 cached
 private module Cached {
@@ -1178,6 +1181,19 @@ private int countNumberOfBranchesUsingParameter(SwitchInstruction switch, Parame
   )
 }
 
+pragma[nomagic]
+private predicate isInputOutput(
+  DF::DataFlowFunction target, Node node1, Node node2, IO::FunctionInput input,
+  IO::FunctionOutput output
+) {
+  exists(CallInstruction call |
+    node1 = callInput(call, input) and
+    node2 = callOutput(call, output) and
+    call.getStaticCallTarget() = target and
+    target.hasDataFlow(input, output)
+  )
+}
+
 /**
  * Holds if the data-flow step from `node1` to `node2` can be used to
  * determine where side-effects may return from a callable.
@@ -1189,6 +1205,11 @@ private int countNumberOfBranchesUsingParameter(SwitchInstruction switch, Parame
  * int x = *p;
  * ```
  * does not preserve the identity of `*p`.
+ *
+ * Similarly, a function that copies the contents of a string into a new location
+ * does not also preserve the identity. For example, `strdup(p)` does not
+ * preserve the identity of `*p` (since it allocates new storage and copies
+ * the string into the new storage).
  */
 bindingset[node1, node2]
 pragma[inline_late]
@@ -1225,7 +1246,16 @@ predicate validParameterAliasStep(Node node1, Node node2) {
   not exists(Operand operand |
     node1.asOperand() = operand and
     node2.asInstruction().(StoreInstruction).getSourceValueOperand() = operand
+  ) and
+  (
+    // Either this is not a modeled flow.
+    not isInputOutput(_, node1, node2, _, _)
+    or
+    exists(DF::DataFlowFunction target, IO::FunctionInput input, IO::FunctionOutput output |
+      // Or it is a modeled flow and there's `*input` to `*output` flow
+      isInputOutput(target, node1, node2, input.getIndirectionInput(), output.getIndirectionOutput()) and
+      // and in that case there should also be `input` to `output` flow
+      target.hasDataFlow(input, output)
+    )
   )
-  // TODO: Also block flow through models that don't preserve identity such
-  // as `strdup`.
 }

cpp/ql/lib/semmle/code/cpp/models/interfaces/FunctionInputsAndOutputs.qll

@@ -23,6 +23,14 @@ private newtype TFunctionInput =
 class FunctionInput extends TFunctionInput {
   abstract string toString();
 
+  /**
+   * INTERNAL: Do not use.
+   *
+   * Gets the `FunctionInput` that represents the indirection of this input,
+   * if any.
+   */
+  FunctionInput getIndirectionInput() { none() }
+
   /**
    * Holds if this is the input value of the parameter with index `index`.
    *
@@ -226,6 +234,8 @@ class InParameter extends FunctionInput, TInParameter {
   ParameterIndex getIndex() { result = index }
 
   override predicate isParameter(ParameterIndex i) { i = index }
+
+  override FunctionInput getIndirectionInput() { result = TInParameterDeref(index, 1) }
 }
 
 /**
@@ -257,6 +267,10 @@ class InParameterDeref extends FunctionInput, TInParameterDeref {
   override predicate isParameterDeref(ParameterIndex i, int indirection) {
     i = index and indirectionIndex = indirection
   }
+
+  override FunctionInput getIndirectionInput() {
+    result = TInParameterDeref(index, indirectionIndex + 1)
+  }
 }
 
 /**
@@ -275,6 +289,8 @@ class InQualifierObject extends FunctionInput, TInQualifierObject {
   override string toString() { result = "InQualifierObject" }
 
   override predicate isQualifierObject() { any() }
+
+  override FunctionInput getIndirectionInput() { none() }
 }
 
 /**
@@ -293,6 +309,8 @@ class InQualifierAddress extends FunctionInput, TInQualifierAddress {
   override string toString() { result = "InQualifierAddress" }
 
   override predicate isQualifierAddress() { any() }
+
+  override FunctionInput getIndirectionInput() { result = TInQualifierObject() }
 }
 
 /**
@@ -321,6 +339,8 @@ class InReturnValueDeref extends FunctionInput, TInReturnValueDeref {
   override string toString() { result = "InReturnValueDeref" }
 
   override predicate isReturnValueDeref() { any() }
+
+  override FunctionInput getIndirectionInput() { none() }
 }
 
 private newtype TFunctionOutput =
@@ -340,6 +360,14 @@ private newtype TFunctionOutput =
 class FunctionOutput extends TFunctionOutput {
   abstract string toString();
 
+  /**
+   * INTERNAL: Do not use.
+   *
+   * Gets the `FunctionOutput` that represents the indirection of this output,
+   * if any.
+   */
+  FunctionOutput getIndirectionOutput() { none() }
+
   /**
    * Holds if this is the output value pointed to by a pointer parameter to a function, or the
    * output value referred to by a reference parameter to a function, where the parameter has
@@ -512,6 +540,10 @@ class OutParameterDeref extends FunctionOutput, TOutParameterDeref {
   override predicate isParameterDeref(ParameterIndex i, int ind) {
     i = index and ind = indirectionIndex
   }
+
+  override FunctionOutput getIndirectionOutput() {
+    result = TOutParameterDeref(index, indirectionIndex + 1)
+  }
 }
 
 /**
@@ -530,6 +562,8 @@ class OutQualifierObject extends FunctionOutput, TOutQualifierObject {
   override string toString() { result = "OutQualifierObject" }
 
   override predicate isQualifierObject() { any() }
+
+  override FunctionOutput getIndirectionOutput() { none() }
 }
 
 /**
@@ -552,6 +586,8 @@ class OutReturnValue extends FunctionOutput, TOutReturnValue {
   override string toString() { result = "OutReturnValue" }
 
   override predicate isReturnValue() { any() }
+
+  override FunctionOutput getIndirectionOutput() { result = TOutReturnValueDeref(1) }
 }
 
 /**
@@ -571,11 +607,19 @@ class OutReturnValue extends FunctionOutput, TOutReturnValue {
  *   of `getInt()` is neither a pointer nor a reference.
  */
 class OutReturnValueDeref extends FunctionOutput, TOutReturnValueDeref {
+  int indirectionIndex;
+
+  OutReturnValueDeref() { this = TOutReturnValueDeref(indirectionIndex) }
+
   override string toString() { result = "OutReturnValueDeref" }
 
   override predicate isReturnValueDeref() { any() }
 
-  override predicate isReturnValueDeref(int indirectionIndex) {
-    this = TOutReturnValueDeref(indirectionIndex)
+  override predicate isReturnValueDeref(int indirectionIndex_) {
+    indirectionIndex = indirectionIndex_
+  }
+
+  override FunctionOutput getIndirectionOutput() {
+    result = TOutReturnValueDeref(indirectionIndex + 1)
   }
 }

cpp/ql/test/library-tests/dataflow/dataflow-tests/TestBase.qll

@@ -49,6 +49,53 @@ module IRTest {
   import semmle.code.cpp.ir.dataflow.DataFlow
   private import semmle.code.cpp.ir.IR
   private import semmle.code.cpp.controlflow.IRGuards
+  private import semmle.code.cpp.models.interfaces.DataFlow
+
+  boolean isOne(string s) {
+    s = "1" and result = true
+    or
+    s = "0" and result = false
+  }
+
+  /**
+   * A model of a test function called `strdup_ptr_xyz` where `x, y, z in {0, 1}`.
+   * `x` is 1 if there's flow from the argument to the function return,
+   * `y` is 1 if there's flow from the first indirection of the argument to
+   * the first indirection of the function return, and
+   * `z` is 1 if there's flow from the second indirection of the argument to
+   * the second indirection of the function return.
+   */
+  class StrDupPtr extends DataFlowFunction {
+    boolean argToReturnFlow;
+    boolean argIndToReturnInd;
+    boolean argIndInToReturnIndInd;
+
+    StrDupPtr() {
+      exists(string r |
+        r = "strdup_ptr_([01])([01])([01])" and
+        argToReturnFlow = isOne(this.getName().regexpCapture(r, 1)) and
+        argIndToReturnInd = isOne(this.getName().regexpCapture(r, 2)) and
+        argIndInToReturnIndInd = isOne(this.getName().regexpCapture(r, 3))
+      )
+    }
+
+    /**
+     * Flow from `**ptr` to `**return`
+     */
+    override predicate hasDataFlow(FunctionInput input, FunctionOutput output) {
+      argToReturnFlow = true and
+      input.isParameter(0) and
+      output.isReturnValue()
+      or
+      argIndToReturnInd = true and
+      input.isParameterDeref(0, 1) and
+      output.isReturnValueDeref(1)
+      or
+      argIndInToReturnIndInd = true and
+      input.isParameterDeref(0, 2) and
+      output.isReturnValueDeref(2)
+    }
+  }
 
   /**
    * A `BarrierGuard` that stops flow to all occurrences of `x` within statement

cpp/ql/test/library-tests/dataflow/dataflow-tests/dataflow-consistency.expected

@@ -24,6 +24,7 @@ postIsInSameCallable
 reverseRead
 argHasPostUpdate
 | flowOut.cpp:55:14:55:16 | * ... | ArgumentNode is missing PostUpdateNode. |
+| flowOut.cpp:185:8:185:9 | * ... | ArgumentNode is missing PostUpdateNode. |
 | lambdas.cpp:18:7:18:7 | a | ArgumentNode is missing PostUpdateNode. |
 | lambdas.cpp:25:2:25:2 | b | ArgumentNode is missing PostUpdateNode. |
 | lambdas.cpp:32:2:32:2 | c | ArgumentNode is missing PostUpdateNode. |
@@ -64,6 +65,8 @@ postWithInFlow
 | flowOut.cpp:90:3:90:4 | * ... [post update] | PostUpdateNode should not be the target of local flow. |
 | flowOut.cpp:90:4:90:4 | q [inner post update] | PostUpdateNode should not be the target of local flow. |
 | flowOut.cpp:101:14:101:14 | p [inner post update] | PostUpdateNode should not be the target of local flow. |
+| flowOut.cpp:168:3:168:10 | * ... [post update] | PostUpdateNode should not be the target of local flow. |
+| flowOut.cpp:168:4:168:10 | toTaint [inner post update] | PostUpdateNode should not be the target of local flow. |
 | globals.cpp:13:5:13:19 | flowTestGlobal1 [post update] | PostUpdateNode should not be the target of local flow. |
 | globals.cpp:23:5:23:19 | flowTestGlobal2 [post update] | PostUpdateNode should not be the target of local flow. |
 | lambdas.cpp:23:3:23:14 | v [post update] | PostUpdateNode should not be the target of local flow. |

cpp/ql/test/library-tests/dataflow/dataflow-tests/dataflow-ir-consistency.expected

@@ -20,6 +20,7 @@ reverseRead
 argHasPostUpdate
 postWithInFlow
 | flowOut.cpp:84:3:84:14 | *access to array | PostUpdateNode should not be the target of local flow. |
+| flowOut.cpp:111:28:111:31 | memcpy output argument | PostUpdateNode should not be the target of local flow. |
 | test.cpp:384:10:384:13 | memcpy output argument | PostUpdateNode should not be the target of local flow. |
 | test.cpp:391:10:391:13 | memcpy output argument | PostUpdateNode should not be the target of local flow. |
 | test.cpp:400:10:400:13 | memcpy output argument | PostUpdateNode should not be the target of local flow. |

cpp/ql/test/library-tests/dataflow/dataflow-tests/flowOut.cpp

@@ -70,7 +70,7 @@ void modify_copy_via_strdup(char* p) { // $ ast-def=p
 
 void test_modify_copy_via_strdup(char* p) { // $ ast-def=p
   modify_copy_via_strdup(p);
-  sink(*p); // $ SPURIOUS: ir
+  sink(*p); // clean
 }
 
 int* deref(int** p) { // $ ast-def=p
@@ -101,3 +101,103 @@ void test2() {
   addtaint2(&p);
   sink(*p); // $ ir MISSING: ast
 }
+
+using size_t = decltype(sizeof(int));
+
+void* memcpy(void* dest, const void* src, size_t);
+
+void modify_copy_via_memcpy(char* p) { // $ ast-def=p
+  char* dest;
+  char* p2 = (char*)memcpy(dest, p, 10);
+  source_ref(p2);
+}
+
+void test_modify_copy_via_memcpy(char* p) { // $ ast-def=p
+  modify_copy_via_memcpy(p);
+  sink(*p); // clean
+}
+
+// These functions from any real database. We add a dataflow model of
+// them as part of dataflow library testing.
+// `r = strdup_ptr_001`(p) has flow from **p to **r
+// `r = strdup_ptr_011`(p) has flow from *p to *r, and **p to **r
+// `r = strdup_ptr_111`(p) has flow from p to r, *p to *r, **p to **r
+char** strdup_ptr_001(const char** p);
+char** strdup_ptr_011(const char** p);
+char** strdup_ptr_111(const char** p);
+
+void source_ref_ref(char** toTaint) { // $ ast-def=toTaint ir-def=*toTaint ir-def=**toTaint 
+  // source -> **toTaint
+  **toTaint = source(true);
+}
+
+// This function copies the value of **p into a new location **p2 and then
+// taints **p. Thus, **p does not contain tainted data after returning from
+// this function.
+void modify_copy_via_strdup_ptr_001(char** p) { // $ ast-def=p
+  // **p -> **p2
+  char** p2 = strdup_ptr_001(p);
+  // source -> **p2
+  source_ref_ref(p2);
+}
+
+void test_modify_copy_via_strdup_001(char** p) { // $ ast-def=p
+  modify_copy_via_strdup_ptr_001(p);
+  sink(**p); // clean
+}
+
+// This function copies the value of *p into a new location *p2 and then
+// taints **p2. Thus, **p contains tainted data after returning from this
+// function.
+void modify_copy_via_strdup_ptr_011(char** p) { // $ ast-def=p
+  // **p -> **p2 and *p -> *p2
+  char** p2 = strdup_ptr_011(p);
+  // source -> **p2
+  source_ref_ref(p2);
+}
+
+void test_modify_copy_via_strdup_011(char** p) { // $ ast-def=p
+  modify_copy_via_strdup_ptr_011(p);
+  sink(**p); // $ ir MISSING: ast
+}
+
+char* source(int);
+
+void source_ref_2(char** toTaint) { // $ ast-def=toTaint ir-def=*toTaint ir-def=**toTaint
+  // source -> *toTaint
+  *toTaint = source(42);
+}
+
+// This function copies the value of p into a new location p2 and then
+// taints *p2. Thus, *p contains tainted data after returning from this
+// function.
+void modify_copy_via_strdup_ptr_111_taint_ind(char** p) { // $ ast-def=p
+  // **p -> **p2, *p -> *p2, and p -> p2
+  char** p2 = strdup_ptr_111(p);
+  // source -> *p2
+  source_ref_2(p2);
+}
+
+void sink(char*);
+
+void test_modify_copy_via_strdup_111_taint_ind(char** p) { // $ ast-def=p
+  modify_copy_via_strdup_ptr_111_taint_ind(p);
+  sink(*p); // $ ir MISSING: ast
+}
+
+// This function copies the value of p into a new location p2 and then
+// taints **p2. Thus, **p contains tainted data after returning from this
+// function.
+void modify_copy_via_strdup_ptr_111_taint_ind_ind(char** p) { // $ ast-def=p
+  // **p -> **p2, *p -> *p2, and p -> p2
+  char** p2 = strdup_ptr_111(p);
+  // source -> **p2
+  source_ref_ref(p2);
+}
+
+void sink(char*);
+
+void test_modify_copy_via_strdup_111_taint_ind_ind(char** p) { // $ ast-def=p
+  modify_copy_via_strdup_ptr_111_taint_ind_ind(p);
+  sink(**p); // $ ir MISSING: ast
+}

cpp/ql/test/library-tests/dataflow/dataflow-tests/test-source-sink.expected

@@ -174,9 +174,11 @@ irFlow
 | dispatch.cpp:144:8:144:13 | call to source | dispatch.cpp:96:8:96:8 | x |
 | flowOut.cpp:5:16:5:21 | call to source | flowOut.cpp:31:9:31:9 | x |
 | flowOut.cpp:5:16:5:21 | call to source | flowOut.cpp:61:8:61:11 | access to array |
-| flowOut.cpp:8:16:8:23 | call to source | flowOut.cpp:73:8:73:9 | * ... |
 | flowOut.cpp:84:18:84:23 | call to source | flowOut.cpp:85:8:85:9 | * ... |
 | flowOut.cpp:90:8:90:13 | call to source | flowOut.cpp:102:8:102:9 | * ... |
+| flowOut.cpp:131:15:131:20 | call to source | flowOut.cpp:161:8:161:10 | * ... |
+| flowOut.cpp:131:15:131:20 | call to source | flowOut.cpp:202:8:202:10 | * ... |
+| flowOut.cpp:168:14:168:19 | call to source | flowOut.cpp:185:8:185:9 | * ... |
 | globals.cpp:5:17:5:22 | call to source | globals.cpp:6:10:6:14 | local |
 | globals.cpp:13:23:13:28 | call to source | globals.cpp:12:10:12:24 | flowTestGlobal1 |
 | globals.cpp:23:23:23:28 | call to source | globals.cpp:19:10:19:24 | flowTestGlobal2 |