[CPP][Linux Kernel]Add ql to detect CVE-2017-5123

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

@@ -0,0 +1,56 @@
+/**
+ * @name Linux kernel no check before unsafe_put_user vulnerability detection
+ * @description unsafe_put_user which is used to write data to user-mode
+ *              memory is widely used in Linux kernel codebase,  but if
+ *              there is no security check for user-mode pointer used as
+ *              parameter of unsafe_put_user, attacker can exploit the issue
+ *              to obtain root privilege. CVE-2017-5123 is quite a good
+ *              example for your information.
+ * @kind problem
+ * @id cpp/linux-kernel-no-check-before-unsafe-put-user
+ * @problem.severity warning
+ * @security-severity 7.5
+ * @tags security
+ *       external/cwe/cwe-020
+ */
+
+import cpp
+import semmle.code.cpp.dataflow.DataFlow
+
+class WriteAccessCheckMacro extends Macro {
+  VariableAccess va;
+
+  WriteAccessCheckMacro() {
+    this.getName() = ["user_write_access_begin", "user_access_begin"] and
+    va.getEnclosingElement() = this.getAnInvocation().getAnExpandedElement()
+  }
+
+  VariableAccess getArgument() { result = va }
+}
+
+class UnSafePutUserMacro extends Macro {
+  PointerDereferenceExpr writeUserPtr;
+
+  UnSafePutUserMacro() {
+    this.getName() = "unsafe_put_user" and
+    writeUserPtr.getEnclosingElement() = this.getAnInvocation().getAnExpandedElement()
+  }
+
+  Expr getUserModePtr() {
+    result = writeUserPtr.getOperand().(AddressOfExpr).getOperand().(FieldAccess).getQualifier()
+  }
+}
+
+class ExploitableUserModePtrParam extends Parameter {
+  ExploitableUserModePtrParam() {
+    not exists(WriteAccessCheckMacro writeAccessCheck |
+      DataFlow::localFlow(DataFlow::parameterNode(this),
+        DataFlow::exprNode(writeAccessCheck.getArgument()))
+    )
+  }
+}
+
+from ExploitableUserModePtrParam p, UnSafePutUserMacro unsafePutUser
+where
+  DataFlow::localFlow(DataFlow::parameterNode(p), DataFlow::exprNode(unsafePutUser.getUserModePtr()))
+select p, "unsafe_put_user write user-mode pointer $@ without check.", p, p.toString()