Merge pull request #16128 from erik-krogh/java-info

Java: add link to the source variable in the alert-message for `java/implicit-cast-in-compound-assignment`

Author: erik-krogh

java/ql/src/Likely Bugs/Arithmetic/InformationLoss.ql

@@ -27,10 +27,23 @@ class DangerousAssignOpExpr extends AssignOp {
 
 predicate problematicCasting(Type t, Expr e) { e.getType().(NumType).widerThan(t) }
 
-from DangerousAssignOpExpr a, Expr e
+Variable getVariable(Expr dest) {
+  result = dest.(VarAccess).getVariable()
+  or
+  result = dest.(ArrayAccess).getArray().(VarAccess).getVariable()
+}
+
+from DangerousAssignOpExpr a, Expr e, Top v
 where
   e = a.getSource() and
-  problematicCasting(a.getDest().getType(), e)
+  problematicCasting(a.getDest().getType(), e) and
+  (
+    v = getVariable(a.getDest())
+    or
+    // fallback, in case we can't easily determine the variable
+    not exists(getVariable(a.getDest())) and
+    v = a.getDest()
+  )
 select a,
-  "Implicit cast of source type " + e.getType().getName() + " to narrower destination type " +
-    a.getDest().getType().getName() + "."
+  "Implicit cast of source type " + e.getType().getName() + " to narrower destination type $@.", v,
+  a.getDest().getType().getName()

java/ql/test/query-tests/security/CWE-190/semmle/tests/InformationLoss.expected

@@ -1,2 +1,4 @@
-| Test.java:68:5:68:25 | ...+=... | Implicit cast of source type long to narrower destination type int. |
-| Test.java:87:4:87:9 | ...+=... | Implicit cast of source type long to narrower destination type int. |
+| Test.java:68:5:68:25 | ...+=... | Implicit cast of source type long to narrower destination type $@. | Test.java:64:4:64:13 | int i | int |
+| Test.java:87:4:87:9 | ...+=... | Implicit cast of source type long to narrower destination type $@. | Test.java:81:4:81:13 | int i | int |
+| Test.java:289:5:289:30 | ...+=... | Implicit cast of source type long to narrower destination type $@. | Test.java:285:4:285:27 | int[] arr | int |
+| Test.java:293:7:293:44 | ...+=... | Implicit cast of source type long to narrower destination type $@. | Test.java:293:7:293:24 | ...[...] | int |

java/ql/test/query-tests/security/CWE-190/semmle/tests/Test.java

@@ -279,12 +279,29 @@ public static void main(String[] args) {
 			// subsequently cast to narrower type int
 			int widenedThenNarrowed = (int) (data2 + 10L);
 		}
+
+    // InformationLoss
+		{
+			int[] arr = new int[10];
+			while (arr[2] < 1000000) {
+				// BAD: getLargeNumber is implicitly narrowed to an integer
+				// which will result in overflows if it is large
+				arr[2] += getLargeNumber();
+			}
+
+      // BAD.
+      getAnIntArray()[0] += getLargeNumber();
+		}
 	}
 
 	public static long getLargeNumber() {
 		return Long.MAX_VALUE / 2;
 	}
 
+  public static int[] getAnIntArray() {
+    return new int[10];
+  }
+
 	public static boolean properlyBounded(int i) {
 		return i < Integer.MAX_VALUE;
 	}