Swift: Proof of concept fix.

Author: geoffw0

swift/ql/lib/codeql/swift/dataflow/internal/DataFlowPrivate.qll

@@ -211,6 +211,8 @@ private predicate modifiable(Argument arg) {
   arg.getExpr() instanceof InOutExpr
   or
   arg.getExpr().getType() instanceof NominalType
+  or
+  arg.getLabel() = "ptr"
 }
 
 predicate modifiableParam(ParamDecl param) {

swift/ql/test/library-tests/dataflow/taint/libraries/unsafepointer.swift

@@ -25,7 +25,7 @@ func taintPointer(ptr: UnsafeMutablePointer<String>) {
 }
 
 func clearPointer2(ptr: UnsafeMutablePointer<String>) {
-  sink(arg: ptr.pointee) // $ MISSING: tainted=21
+  sink(arg: ptr.pointee) // $ tainted=21
   sink(arg: ptr)
 
   ptr.pointee = "abc"
@@ -42,12 +42,12 @@ func testMutatingPointerInCall(ptr: UnsafeMutablePointer<String>) {
 
   taintPointer(ptr: ptr) // mutates `ptr` pointee with a tainted value
 
-  sink(arg: ptr.pointee) // $ MISSING: tainted=21
+  sink(arg: ptr.pointee) // $ tainted=21
   sink(arg: ptr)
 
   clearPointer2(ptr: ptr)
 
-  sink(arg: ptr.pointee)
+  sink(arg: ptr.pointee) // $ SPURIOUS: tainted=21
   sink(arg: ptr)
 }
 
@@ -96,6 +96,6 @@ func testMutatingMyPointerInCall(ptr: MyPointer) {
 
   taintMyPointer(ptr: ptr) // mutates `ptr` pointee with a tainted value
 
-  sink(arg: ptr.pointee) // $ MISSING: tainted=87
+  sink(arg: ptr.pointee) // $ tainted=87
   sink(arg: ptr)
 }