C++: Propagate flow from instruction's to non-exact operands for arrays and unions, and accept test changes.

Author: MathiasVP

cpp/ql/src/semmle/code/cpp/ir/dataflow/DefaultTaintTracking.qll

@@ -210,6 +210,19 @@ private predicate commonTaintStep(DataFlow::Node fromNode, DataFlow::Node toNode
 }
 
 private predicate instructionToOperandTaintStep(Instruction fromInstr, Operand toOperand) {
+  // Propagate flow from the definition of an operand to the operand, even when the overlap is inexact.
+  // We only do this in certain cases:
+  // 1. The instruction's result must not be conflated, and
+  // 2. The instruction's result type is one the types where we expect element-to-object flow. Currently
+  // this array types and union types. This matches the other two cases of element-to-object flow in
+  // `DefaultTaintTracking`.
+  toOperand.getAnyDef() = fromInstr and
+  not fromInstr.isResultConflated() and
+  (
+    fromInstr.getResultType() instanceof ArrayType or
+    fromInstr.getResultType() instanceof Union
+  )
+  or
   exists(ReadSideEffectInstruction readInstr |
     fromInstr = readInstr.getArgumentDef() and
     toOperand = readInstr.getSideEffectOperand()

cpp/ql/test/query-tests/Security/CWE/CWE-134/semmle/globalVars/UncontrolledFormatStringThroughGlobalVar.expected

@@ -4,12 +4,14 @@ edges
 | globalVars.c:8:7:8:10 | copy | globalVars.c:27:9:27:12 | copy |
 | globalVars.c:8:7:8:10 | copy | globalVars.c:30:15:30:18 | copy |
 | globalVars.c:8:7:8:10 | copy | globalVars.c:30:15:30:18 | copy |
+| globalVars.c:8:7:8:10 | copy | globalVars.c:30:15:30:18 | copy |
 | globalVars.c:8:7:8:10 | copy | globalVars.c:35:11:35:14 | copy |
 | globalVars.c:9:7:9:11 | copy2 | globalVars.c:38:9:38:13 | copy2 |
 | globalVars.c:9:7:9:11 | copy2 | globalVars.c:38:9:38:13 | copy2 |
 | globalVars.c:9:7:9:11 | copy2 | globalVars.c:38:9:38:13 | copy2 |
 | globalVars.c:9:7:9:11 | copy2 | globalVars.c:41:15:41:19 | copy2 |
 | globalVars.c:9:7:9:11 | copy2 | globalVars.c:41:15:41:19 | copy2 |
+| globalVars.c:9:7:9:11 | copy2 | globalVars.c:41:15:41:19 | copy2 |
 | globalVars.c:9:7:9:11 | copy2 | globalVars.c:50:9:50:13 | copy2 |
 | globalVars.c:9:7:9:11 | copy2 | globalVars.c:50:9:50:13 | copy2 |
 | globalVars.c:9:7:9:11 | copy2 | globalVars.c:50:9:50:13 | copy2 |
@@ -25,9 +27,15 @@ edges
 | globalVars.c:24:11:24:14 | argv | globalVars.c:11:22:11:25 | argv |
 | globalVars.c:27:9:27:12 | copy | globalVars.c:27:9:27:12 | (const char *)... |
 | globalVars.c:27:9:27:12 | copy | globalVars.c:27:9:27:12 | copy |
+| globalVars.c:30:15:30:18 | copy | globalVars.c:30:15:30:18 | copy |
+| globalVars.c:30:15:30:18 | copy | globalVars.c:30:15:30:18 | copy |
+| globalVars.c:30:15:30:18 | copy | globalVars.c:30:15:30:18 | copy |
 | globalVars.c:35:11:35:14 | copy | globalVars.c:15:21:15:23 | val |
 | globalVars.c:38:9:38:13 | copy2 | globalVars.c:38:9:38:13 | (const char *)... |
 | globalVars.c:38:9:38:13 | copy2 | globalVars.c:38:9:38:13 | copy2 |
+| globalVars.c:41:15:41:19 | copy2 | globalVars.c:41:15:41:19 | copy2 |
+| globalVars.c:41:15:41:19 | copy2 | globalVars.c:41:15:41:19 | copy2 |
+| globalVars.c:41:15:41:19 | copy2 | globalVars.c:41:15:41:19 | copy2 |
 | globalVars.c:50:9:50:13 | copy2 | globalVars.c:50:9:50:13 | (const char *)... |
 | globalVars.c:50:9:50:13 | copy2 | globalVars.c:50:9:50:13 | copy2 |
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