Understand syscalls better.

Author: geoffw0

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

@@ -22,15 +22,18 @@ import semmle.code.cpp.dataflow.DataFlow
  */
 class SystemCallFunction extends Function {
   SystemCallFunction() {
-    this.getName().matches("SYSC\\_%")
+    exists(MacroInvocation m |
+      m.getMacro().getName().matches("SYSCALL\\_DEFINE%") and
+      this = m.getEnclosingFunction()
+    )
   }
 }
 
 /**
  * A value that comes from a Linux system call (sources).
  */
-class SystemParameterSource extends DataFlow::Node {
-  SystemParameterSource() {
+class SystemCallSource extends DataFlow::Node {
+  SystemCallSource() {
     exists(FunctionCall fc |
       fc.getTarget() instanceof SystemCallFunction and
       (
@@ -72,7 +75,7 @@ class UnSafePutUserMacro extends Macro {
   }
 }
 
-class ExploitableUserModePtrParam extends SystemParameterSource {
+class ExploitableUserModePtrParam extends SystemCallSource {
   ExploitableUserModePtrParam() {
     exists(UnSafePutUserMacro unsafePutUser |
       DataFlow::localFlow(this, DataFlow::exprNode(unsafePutUser.getUserModePtr()))

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

@@ -1,3 +1,3 @@
-| 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 & ... |
+| test.cpp:20:21:20:22 | ref arg & ... | unsafe_put_user write user-mode pointer $@ without check. | test.cpp:20:21:20:22 | ref arg & ... | ref arg & ... |
+| test.cpp:41:21:41:22 | ref arg & ... | unsafe_put_user write user-mode pointer $@ without check. | test.cpp:41:21:41:22 | ref arg & ... | ref arg & ... |
+| test.cpp:69:21:69:27 | ref arg & ... | unsafe_put_user write user-mode pointer $@ without check. | test.cpp:69:21:69:27 | ref arg & ... | ref arg & ... |

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

@@ -1,7 +1,11 @@
 
 typedef unsigned long size_t;
 
-void SYSC_SOMESYSTEMCALL(void *param);
+#define SYSCALL_DEFINE(name, ...) \
+	void do_sys_##name(); \
+	void sys_##name(...) { do_sys_##name(); } \
+	void do_sys_##name()
+SYSCALL_DEFINE(somesystemcall, void *param) {};
 
 bool user_access_begin_impl(const void *where, size_t sz);
 void user_access_end_impl();
@@ -13,14 +17,14 @@ void unsafe_put_user_impl(int what, const void *where, size_t sz);
 
 void test1(int p)
 {
-	SYSC_SOMESYSTEMCALL(&p);
+	sys_somesystemcall(&p);
 
 	unsafe_put_user(123, &p); // BAD
 }
 
 void test2(int p)
 {
-	SYSC_SOMESYSTEMCALL(&p);
+	sys_somesystemcall(&p);
 
 	if (user_access_begin(&p, sizeof(p)))
 	{
@@ -34,7 +38,7 @@ void test3()
 {
 	int v;
 
-	SYSC_SOMESYSTEMCALL(&v);
+	sys_somesystemcall(&v);
 
 	unsafe_put_user(123, &v); // BAD
 }
@@ -43,7 +47,7 @@ void test4()
 {
 	int v;
 
-	SYSC_SOMESYSTEMCALL(&v);
+	sys_somesystemcall(&v);
 
 	if (user_access_begin(&v, sizeof(v)))
 	{
@@ -62,7 +66,7 @@ void test5()
 {
 	data myData;
 
-	SYSC_SOMESYSTEMCALL(&myData);
+	sys_somesystemcall(&myData);
 
 	unsafe_put_user(123, &(myData.x)); // BAD
 }
@@ -71,7 +75,7 @@ void test6()
 {
 	data myData;
 
-	SYSC_SOMESYSTEMCALL(&myData);
+	sys_somesystemcall(&myData);
 
 	if (user_access_begin(&myData, sizeof(myData)))
 	{