C++: Add false positive testcase when an absolute value is used in comparison.

Author: MathiasVP

cpp/ql/test/query-tests/Security/CWE/CWE-190/semmle/tainted/ArithmeticTainted.expected

@@ -3,6 +3,10 @@
 | test5.cpp:17:6:17:18 | call to getTaintedInt | $@ flows to here and is used in arithmetic, potentially causing an overflow. | test5.cpp:9:7:9:9 | buf | User-provided value |
 | test5.cpp:19:6:19:6 | y | $@ flows to here and is used in arithmetic, potentially causing an overflow. | test5.cpp:9:7:9:9 | buf | User-provided value |
 | test5.cpp:19:6:19:6 | y | $@ flows to here and is used in arithmetic, potentially causing an underflow. | test5.cpp:9:7:9:9 | buf | User-provided value |
+| test5.cpp:30:17:30:23 | tainted | $@ flows to here and is used in arithmetic, potentially causing an overflow. | test5.cpp:9:7:9:9 | buf | User-provided value |
+| test5.cpp:30:17:30:23 | tainted | $@ flows to here and is used in arithmetic, potentially causing an underflow. | test5.cpp:9:7:9:9 | buf | User-provided value |
+| test5.cpp:30:27:30:33 | tainted | $@ flows to here and is used in arithmetic, potentially causing an overflow. | test5.cpp:9:7:9:9 | buf | User-provided value |
+| test5.cpp:30:27:30:33 | tainted | $@ flows to here and is used in arithmetic, potentially causing an underflow. | test5.cpp:9:7:9:9 | buf | User-provided value |
 | test.c:14:15:14:28 | maxConnections | $@ flows to here and is used in arithmetic, potentially causing an overflow. | test.c:11:29:11:32 | argv | User-provided value |
 | test.c:14:15:14:28 | maxConnections | $@ flows to here and is used in arithmetic, potentially causing an underflow. | test.c:11:29:11:32 | argv | User-provided value |
 | test.c:44:7:44:10 | len2 | $@ flows to here and is used in arithmetic, potentially causing an underflow. | test.c:41:17:41:20 | argv | User-provided value |

cpp/ql/test/query-tests/Security/CWE/CWE-190/semmle/tainted/test5.cpp

@@ -18,3 +18,15 @@ void useTaintedInt()
 	y = getTaintedInt();
 	y = y * 1024; // BAD: arithmetic on a tainted value
 }
+
+typedef long long int intmax_t;
+
+intmax_t imaxabs(intmax_t j);
+
+void useTaintedIntWithGuard() {
+	int tainted = getTaintedInt();
+
+	if(imaxabs(tainted) <= 100) {
+		int product = tainted * tainted; // GOOD: can't underflow/overflow [FALSE POSITIVE]
+	}
+}