CPP: Add query for CWE-476: NULL Pointer Dereference when using exception handling blocks

cpp/ql/src/experimental/Security/CWE/CWE-476/DangerousUseOfExceptionBlocks.cpp

@@ -0,0 +1,48 @@
+...
+try {
+  if (checkValue) throw exception();
+  bufMyData =  new myData*[sizeInt];
+
+  } 
+  catch (...) 
+  {
+    for (size_t i = 0; i < sizeInt; i++)
+    {
+    	delete[] bufMyData[i]->buffer; // BAD
+        delete bufMyData[i];
+    }
+...
+try {
+  if (checkValue) throw exception();
+  bufMyData =  new myData*[sizeInt];
+
+  } 
+  catch (...) 
+  {
+    for (size_t i = 0; i < sizeInt; i++)
+    {
+      if(bufMyData[i])
+      {
+    	delete[] bufMyData[i]->buffer; // GOOD
+        delete bufMyData[i];
+      }
+    }
+
+...
+  catch (const exception &) {
+	  delete valData;
+	  throw;
+  }
+  catch (...) 
+  {
+    delete valData; // BAD
+...
+  catch (const exception &) {
+	  delete valData;
+    valData = NULL;
+	  throw;
+  }
+  catch (...) 
+  {
+    delete valData; // GOOD  
+...

cpp/ql/src/experimental/Security/CWE/CWE-476/DangerousUseOfExceptionBlocks.qhelp

@@ -0,0 +1,23 @@
+<!DOCTYPE qhelp PUBLIC
+  "-//Semmle//qhelp//EN"
+  "qhelp.dtd">
+<qhelp>
+<overview>
+<p>When releasing memory in a catch block, be sure that the memory was allocated and has not already been released.</p>
+
+</overview>
+
+<example>
+<p>The following example shows erroneous and fixed ways to use exception handling.</p>
+<sample src="DangerousUseOfExceptionBlocks.cpp" />
+
+</example>
+<references>
+
+<li>
+  CERT C Coding Standard:
+  <a href="https://wiki.sei.cmu.edu/confluence/display/c/EXP34-C.+Do+not+dereference+null+pointers">EXP34-C. Do not dereference null pointers</a>.
+</li>
+
+</references>
+</qhelp>

cpp/ql/src/experimental/Security/CWE/CWE-476/DangerousUseOfExceptionBlocks.ql

@@ -0,0 +1,199 @@
+/**
+ * @name Dangerous use of exception blocks.
+ * @description When clearing the data in the catch block, you must be sure that the memory was allocated before the exception.
+ * @kind problem
+ * @id cpp/dangerous-use-of-exception-blocks
+ * @problem.severity warning
+ * @precision medium
+ * @tags correctness
+ *       security
+ *       external/cwe/cwe-476
+ *       external/cwe/cwe-415
+ */
+
+import cpp
+
+/** Holds if `vr` may be released in the `try` block associated with `cb`, or in a `catch` block prior to `cb`. */
+pragma[inline]
+predicate doubleCallDelete(BlockStmt b, CatchAnyBlock cb, Variable vr) {
+  // Search for exceptions after freeing memory.
+  exists(Expr e1 |
+    // `e1` is a delete of `vr`
+    (
+      e1 = vr.getAnAccess().getEnclosingStmt().(ExprStmt).getExpr().(DeleteArrayExpr) or
+      e1 = vr.getAnAccess().getEnclosingStmt().(ExprStmt).getExpr().(DeleteExpr)
+    ) and
+    e1.getEnclosingFunction() = cb.getEnclosingFunction() and
+    // there is no assignment `vr = 0` in the `try` block after `e1`
+    not exists(AssignExpr ae |
+      ae.getLValue().(VariableAccess).getTarget() = vr and
+      ae.getRValue().getValue() = "0" and
+      e1.getASuccessor+() = ae and
+      ae.getEnclosingStmt().getParentStmt*() = b
+    ) and
+    // `e2` is a `throw` (or a function call that may throw) that occurs in the `try` or `catch` block after `e1`
+    exists(Expr e2, ThrowExpr th |
+      (
+        e2 = th or
+        e2 = th.getEnclosingFunction().getACallToThisFunction()
+      ) and
+      e2.getEnclosingStmt().getParentStmt*() = b and
+      e1.getASuccessor+() = e2
+    ) and
+    e1.getEnclosingStmt().getParentStmt*() = b and
+    (
+      // Search for a situation where there is a release in the block of `try`.
+      b = cb.getTryStmt().getStmt()
+      or
+      // Search for a situation when there is a higher catch block that also frees memory.
+      exists(b.(CatchBlock).getParameter())
+    ) and
+    // Exclude the presence of a check in catch block.
+    not exists(IfStmt ifst | ifst.getEnclosingStmt().getParentStmt*() = cb.getAStmt())
+  )
+}
+
+/** Holds if an exception can be thrown before the memory is allocated, and when the exception is handled, an attempt is made to access unallocated memory in the catch block. */
+pragma[inline]
+predicate pointerDereference(CatchAnyBlock cb, Variable vr, Variable vro) {
+  // Search exceptions before allocating memory.
+  exists(Expr e0, Expr e1 |
+    (
+      // `e0` is a `new` expression (or equivalent function call) assigned to `vro`
+      exists(AssignExpr ase |
+        ase = vro.getAnAccess().getEnclosingStmt().(ExprStmt).getExpr() and
+        (
+          e0 = ase.getRValue().(NewOrNewArrayExpr) or
+          e0 = ase.getRValue().(NewOrNewArrayExpr).getEnclosingFunction().getACallToThisFunction()
+        ) and
+        vro = ase.getLValue().(VariableAccess).getTarget()
+      )
+      or
+      // `e0` is a `new` expression (or equivalent function call) assigned to the array element `vro`
+      exists(AssignExpr ase |
+        ase = vro.getAnAccess().(Qualifier).getEnclosingStmt().(ExprStmt).getExpr() and
+        (
+          e0 = ase.getRValue().(NewOrNewArrayExpr) or
+          e0 = ase.getRValue().(NewOrNewArrayExpr).getEnclosingFunction().getACallToThisFunction()
+        ) and
+        not ase.getLValue() instanceof VariableAccess and
+        vro = ase.getLValue().getAPredecessor().(VariableAccess).getTarget()
+      )
+    ) and
+    // `e1` is a `new` expression (or equivalent function call) assigned to `vr`
+    exists(AssignExpr ase |
+      ase = vr.getAnAccess().getEnclosingStmt().(ExprStmt).getExpr() and
+      (
+        e1 = ase.getRValue().(NewOrNewArrayExpr) or
+        e1 = ase.getRValue().(NewOrNewArrayExpr).getEnclosingFunction().getACallToThisFunction()
+      ) and
+      vr = ase.getLValue().(VariableAccess).getTarget()
+    ) and
+    e0.getASuccessor*() = e1 and
+    e0.getEnclosingStmt().getParentStmt*() = cb.getTryStmt().getStmt() and
+    e1.getEnclosingStmt().getParentStmt*() = cb.getTryStmt().getStmt() and
+    // `e2` is a `throw` (or a function call that may throw) that occurs in the `try` block before `e0`
+    exists(Expr e2, ThrowExpr th |
+      (
+        e2 = th or
+        e2 = th.getEnclosingFunction().getACallToThisFunction()
+      ) and
+      e2.getEnclosingStmt().getParentStmt*() = cb.getTryStmt().getStmt() and
+      e2.getASuccessor+() = e0
+    )
+  ) and
+  // We exclude checking the value of a variable or its parent in the catch block.
+  not exists(IfStmt ifst |
+    ifst.getEnclosingStmt().getParentStmt*() = cb.getAStmt() and
+    (
+      ifst.getCondition().getAChild*().(VariableAccess).getTarget() = vr or
+      ifst.getCondition().getAChild*().(VariableAccess).getTarget() = vro
+    )
+  )
+}
+
+/** Holds if `vro` may be released in the `catch`. */
+pragma[inline]
+predicate newThrowDelete(CatchAnyBlock cb, Variable vro) {
+  exists(Expr e0, AssignExpr ase, NewOrNewArrayExpr nae |
+    ase = vro.getAnAccess().getEnclosingStmt().(ExprStmt).getExpr() and
+    nae = ase.getRValue() and
+    not nae.getAChild*().toString() = "nothrow" and
+    (
+      e0 = nae or
+      e0 = nae.getEnclosingFunction().getACallToThisFunction()
+    ) and
+    vro = ase.getLValue().(VariableAccess).getTarget() and
+    e0.getEnclosingStmt().getParentStmt*() = cb.getTryStmt().getStmt() and
+    not exists(AssignExpr ase1 |
+      vro = ase1.getLValue().(VariableAccess).getTarget() and
+      ase1.getRValue().getValue() = "0" and
+      ase1.getASuccessor*() = e0
+    )
+  ) and
+  not exists(Initializer it |
+    vro.getInitializer() = it and
+    it.getExpr().getValue() = "0"
+  ) and
+  not exists(ConstructorFieldInit ci | vro = ci.getTarget())
+}
+
+from CatchAnyBlock cb, string msg
+where
+  exists(Variable vr, Variable vro, Expr exp |
+    exp.getEnclosingStmt().getParentStmt*() = cb and
+    exists(VariableAccess va |
+      (
+        (
+          va = exp.(DeleteArrayExpr).getExpr().getAPredecessor+().(Qualifier) or
+          va = exp.(DeleteArrayExpr).getExpr().getAPredecessor+()
+        ) and
+        vr = exp.(DeleteArrayExpr).getExpr().(VariableAccess).getTarget()
+        or
+        (
+          va = exp.(DeleteExpr).getExpr().getAPredecessor+().(Qualifier) or
+          va = exp.(DeleteExpr).getExpr().getAPredecessor+()
+        ) and
+        vr = exp.(DeleteExpr).getExpr().(VariableAccess).getTarget()
+      ) and
+      va.getEnclosingStmt() = exp.getEnclosingStmt() and
+      vro = va.getTarget() and
+      vr != vro
+    ) and
+    pointerDereference(cb, vr, vro) and
+    msg =
+      "it is possible to dereference a pointer when accessing a " + vr.getName() +
+        ", since it is possible to throw an exception before the memory for the " + vro.getName() +
+        " is allocated"
+  )
+  or
+  exists(Expr exp, Variable vr |
+    (
+      exp.(DeleteExpr).getEnclosingStmt().getParentStmt*() = cb and
+      vr = exp.(DeleteExpr).getExpr().(VariableAccess).getTarget()
+      or
+      exp.(DeleteArrayExpr).getEnclosingStmt().getParentStmt*() = cb and
+      vr = exp.(DeleteArrayExpr).getExpr().(VariableAccess).getTarget()
+    ) and
+    doubleCallDelete(_, cb, vr) and
+    msg =
+      "This allocation may have been released in the try block or a previous catch block." +
+        vr.getName()
+  )
+  or
+  exists(Variable vro, Expr exp |
+    exp.getEnclosingStmt().getParentStmt*() = cb and
+    exists(VariableAccess va |
+      (
+        va = exp.(DeleteArrayExpr).getExpr() or
+        va = exp.(DeleteExpr).getExpr()
+      ) and
+      va.getEnclosingStmt() = exp.getEnclosingStmt() and
+      vro = va.getTarget()
+    ) and
+    newThrowDelete(cb, vro) and
+    msg =
+      "If the allocation in the try block fails, then an unallocated pointer " + vro.getName() +
+        " will be freed in the catch block."
+  )
+select cb, msg

cpp/ql/test/experimental/query-tests/Security/CWE/CWE-476/semmle/tests/DangerousUseOfExceptionBlocks.expected

@@ -0,0 +1,8 @@
+| test.cpp:63:3:71:3 | { ... } | If the allocation in the try block fails, then an unallocated pointer bufMyData will be freed in the catch block. |
+| test.cpp:63:3:71:3 | { ... } | If the allocation in the try block fails, then an unallocated pointer buffer will be freed in the catch block. |
+| test.cpp:63:3:71:3 | { ... } | it is possible to dereference a pointer when accessing a buffer, since it is possible to throw an exception before the memory for the bufMyData is allocated |
+| test.cpp:91:3:100:3 | { ... } | If the allocation in the try block fails, then an unallocated pointer buffer will be freed in the catch block. |
+| test.cpp:120:3:128:3 | { ... } | If the allocation in the try block fails, then an unallocated pointer buffer will be freed in the catch block. |
+| test.cpp:143:3:151:3 | { ... } | If the allocation in the try block fails, then an unallocated pointer buffer will be freed in the catch block. |
+| test.cpp:181:3:183:3 | { ... } | This allocation may have been released in the try block or a previous catch block.valData |
+| test.cpp:219:3:221:3 | { ... } | This allocation may have been released in the try block or a previous catch block.valData |

cpp/ql/test/experimental/query-tests/Security/CWE/CWE-476/semmle/tests/DangerousUseOfExceptionBlocks.qlref

@@ -0,0 +1 @@
+experimental/Security/CWE/CWE-476/DangerousUseOfExceptionBlocks.ql