C++: Define sources better so that we catch all the test cases.

Author: geoffw0

cpp/ql/src/experimental/Security/CWE/CWE-020/NoCheckBeforeUnsafePutUser.ql

@@ -17,6 +17,33 @@
 import cpp
 import semmle.code.cpp.dataflow.DataFlow
 
+/**
+ * A Linux system call.
+ */
+class SystemCallFunction extends Function {
+  SystemCallFunction() {
+    this.getName().matches("SYSC\\_%")
+  }
+}
+
+/**
+ * A value that comes from a Linux system call (sources).
+ */
+class SystemParameterSource extends DataFlow::Node {
+  SystemParameterSource() {
+    exists(FunctionCall fc |
+      fc.getTarget() instanceof SystemCallFunction and
+      (
+        this.asDefiningArgument() = fc.getAnArgument().getAChild*() or
+        this.asExpr() = fc
+      )
+    )
+  }
+}
+
+/**
+ * Macros used to check the value (barriers).
+ */
 class WriteAccessCheckMacro extends Macro {
   VariableAccess va;
 
@@ -28,6 +55,9 @@ class WriteAccessCheckMacro extends Macro {
   VariableAccess getArgument() { result = va }
 }
 
+/**
+ * The `unsafe_put_user` macro and its uses (sinks).
+ */
 class UnSafePutUserMacro extends Macro {
   PointerDereferenceExpr writeUserPtr;
 
@@ -42,15 +72,13 @@ class UnSafePutUserMacro extends Macro {
   }
 }
 
-class ExploitableUserModePtrParam extends Parameter {
+class ExploitableUserModePtrParam extends SystemParameterSource {
   ExploitableUserModePtrParam() {
-    not exists(WriteAccessCheckMacro writeAccessCheck |
-      DataFlow::localFlow(DataFlow::parameterNode(this),
-        DataFlow::exprNode(writeAccessCheck.getArgument()))
-    ) and
     exists(UnSafePutUserMacro unsafePutUser |
-      DataFlow::localFlow(DataFlow::parameterNode(this),
-        DataFlow::exprNode(unsafePutUser.getUserModePtr()))
+      DataFlow::localFlow(this, DataFlow::exprNode(unsafePutUser.getUserModePtr()))
+    ) and
+    not exists(WriteAccessCheckMacro writeAccessCheck |
+      DataFlow::localFlow(this, DataFlow::exprNode(writeAccessCheck.getArgument()))
     )
   }
 }

cpp/ql/test/experimental/query-tests/Security/CWE/CWE-020/NoCheckBeforeUnsafePutUser/NoCheckBeforeUnsafePutUser.expected

@@ -1 +1,3 @@
-| test.cpp:14:16:14:16 | p | unsafe_put_user write user-mode pointer $@ without check. | test.cpp:14:16:14:16 | p | p |
+| test.cpp:16:22:16:23 | ref arg & ... | unsafe_put_user write user-mode pointer $@ without check. | test.cpp:16:22:16:23 | ref arg & ... | ref arg & ... |
+| test.cpp:37:22:37:23 | ref arg & ... | unsafe_put_user write user-mode pointer $@ without check. | test.cpp:37:22:37:23 | ref arg & ... | ref arg & ... |
+| test.cpp:65:22:65:28 | ref arg & ... | unsafe_put_user write user-mode pointer $@ without check. | test.cpp:65:22:65:28 | ref arg & ... | ref arg & ... |

cpp/ql/test/experimental/query-tests/Security/CWE/CWE-020/NoCheckBeforeUnsafePutUser/test.cpp

@@ -36,7 +36,7 @@ void test3()
 
 	SYSC_SOMESYSTEMCALL(&v);
 
-	unsafe_put_user(123, &v); // BAD [NOT DETECTED]
+	unsafe_put_user(123, &v); // BAD
 }
 
 void test4()
@@ -64,7 +64,7 @@ void test5()
 
 	SYSC_SOMESYSTEMCALL(&myData);
 
-	unsafe_put_user(123, &(myData.x)); // BAD [NOT DETECTED]
+	unsafe_put_user(123, &(myData.x)); // BAD
 }
 
 void test6()