C++: Tweak the bounded barrier

cpp/ql/src/Security/CWE/CWE-190/Bounded.qll

@@ -1,27 +1,25 @@
 /**
- * This file provides the `bounded` predicate that is used in both `cpp/uncontrolled-arithmetic`
- * and `cpp/tainted-arithmetic`.
+ * This file provides the `bounded` predicate that is used in `cpp/uncontrolled-arithmetic`,
+ * `cpp/tainted-arithmetic` and `cpp/uncontrolled-allocation-size`.
  */
 
 private import cpp
 private import semmle.code.cpp.rangeanalysis.SimpleRangeAnalysis
 private import semmle.code.cpp.rangeanalysis.RangeAnalysisUtils
 
 /**
- * An operand `e` of a bitwise and expression `andExpr` (i.e., `andExpr` is either an `BitwiseAndExpr`
- * or an `AssignAndExpr`) with operands `operand1` and `operand2` is the operand that is not `e` is upper
- * bounded by some number that is less than the maximum integer allowed by the result type of `andExpr`.
+ * An operand `operand` of a bitwise and expression `andExpr` (i.e., `andExpr` is either a
+ * `BitwiseAndExpr` or an `AssignAndExpr`) is upper bounded by some number that is less than the
+ * maximum integer allowed by the result type of `andExpr`.
  */
 pragma[inline]
-private predicate boundedBitwiseAnd(Expr e, Expr andExpr, Expr operand1, Expr operand2) {
-  operand1 != operand2 and
-  e = operand1 and
-  upperBound(operand2.getFullyConverted()) < exprMaxVal(andExpr.getFullyConverted())
+private predicate boundedBitwiseAnd(Expr operand, Expr andExpr) {
+  upperBound(operand.getFullyConverted()) < exprMaxVal(andExpr.getFullyConverted())
 }
 
 /**
- * Holds if `e` is an arithmetic expression that cannot overflow, or if `e` is an operand of an
- * operation that may greatly reduce the range of possible values.
+ * Holds if `e` is an arithmetic expression that cannot overflow, or if `e` is an operation that
+ * may greatly reduce the range of possible values.
  */
 predicate bounded(Expr e) {
   // There can be two separate reasons for `convertedExprMightOverflow` not holding:
@@ -35,25 +33,25 @@ predicate bounded(Expr e) {
   ) and
   not convertedExprMightOverflow(e)
   or
-  // Optimistically assume that a remainder expression always yields a much smaller value.
-  e = any(RemExpr rem).getLeftOperand()
+  // Optimistically assume that the following operations always yields a much smaller value.
+  e instanceof RemExpr
   or
-  e = any(AssignRemExpr rem).getLValue()
+  e instanceof DivExpr
   or
-  exists(BitwiseAndExpr andExpr |
-    boundedBitwiseAnd(e, andExpr, andExpr.getAnOperand(), andExpr.getAnOperand())
-  )
+  e instanceof RShiftExpr
   or
-  exists(AssignAndExpr andExpr |
-    boundedBitwiseAnd(e, andExpr, andExpr.getAnOperand(), andExpr.getAnOperand())
+  exists(BitwiseAndExpr andExpr |
+    e = andExpr and boundedBitwiseAnd(andExpr.getAnOperand(), andExpr)
   )
   or
-  // Optimistically assume that a division always yields a much smaller value.
-  e = any(DivExpr div).getLeftOperand()
+  // For the assignment variant of the operations we place the barrier on the assigned lvalue.
+  e = any(AssignRemExpr rem).getLValue()
   or
   e = any(AssignDivExpr div).getLValue()
   or
-  e = any(RShiftExpr shift).getLeftOperand()
-  or
   e = any(AssignRShiftExpr div).getLValue()
+  or
+  exists(AssignAndExpr andExpr |
+    e = andExpr.getLValue() and boundedBitwiseAnd(andExpr.getRValue(), andExpr)
+  )
 }

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

@@ -32,6 +32,8 @@ edges
 | test.cpp:24:11:24:18 | call to get_rand | test.cpp:25:7:25:7 | r | provenance |  |
 | test.cpp:30:13:30:14 | get_rand2 output argument | test.cpp:31:7:31:7 | r | provenance |  |
 | test.cpp:36:13:36:13 | get_rand3 output argument | test.cpp:37:7:37:7 | r | provenance |  |
+| test.cpp:62:19:62:24 | call to rand | test.cpp:62:19:62:24 | call to rand | provenance |  |
+| test.cpp:62:19:62:24 | call to rand | test.cpp:65:9:65:9 | x | provenance |  |
 | test.cpp:86:10:86:13 | call to rand | test.cpp:86:10:86:13 | call to rand | provenance |  |
 | test.cpp:86:10:86:13 | call to rand | test.cpp:90:10:90:10 | x | provenance |  |
 | test.cpp:98:10:98:13 | call to rand | test.cpp:98:10:98:13 | call to rand | provenance |  |
@@ -105,6 +107,9 @@ nodes
 | test.cpp:31:7:31:7 | r | semmle.label | r |
 | test.cpp:36:13:36:13 | get_rand3 output argument | semmle.label | get_rand3 output argument |
 | test.cpp:37:7:37:7 | r | semmle.label | r |
+| test.cpp:62:19:62:24 | call to rand | semmle.label | call to rand |
+| test.cpp:62:19:62:24 | call to rand | semmle.label | call to rand |
+| test.cpp:65:9:65:9 | x | semmle.label | x |
 | test.cpp:86:10:86:13 | call to rand | semmle.label | call to rand |
 | test.cpp:86:10:86:13 | call to rand | semmle.label | call to rand |
 | test.cpp:90:10:90:10 | x | semmle.label | x |
@@ -156,6 +161,7 @@ subpaths
 | test.cpp:25:7:25:7 | r | test.cpp:8:9:8:12 | call to rand | test.cpp:25:7:25:7 | r | This arithmetic expression depends on an $@, potentially causing an overflow. | test.cpp:8:9:8:12 | call to rand | uncontrolled value |
 | test.cpp:31:7:31:7 | r | test.cpp:13:10:13:13 | call to rand | test.cpp:31:7:31:7 | r | This arithmetic expression depends on an $@, potentially causing an overflow. | test.cpp:13:10:13:13 | call to rand | uncontrolled value |
 | test.cpp:37:7:37:7 | r | test.cpp:18:9:18:12 | call to rand | test.cpp:37:7:37:7 | r | This arithmetic expression depends on an $@, potentially causing an overflow. | test.cpp:18:9:18:12 | call to rand | uncontrolled value |
+| test.cpp:65:9:65:9 | x | test.cpp:62:19:62:24 | call to rand | test.cpp:65:9:65:9 | x | This arithmetic expression depends on an $@, potentially causing an underflow. | test.cpp:62:19:62:22 | call to rand | uncontrolled value |
 | test.cpp:90:10:90:10 | x | test.cpp:86:10:86:13 | call to rand | test.cpp:90:10:90:10 | x | This arithmetic expression depends on an $@, potentially causing an overflow. | test.cpp:86:10:86:13 | call to rand | uncontrolled value |
 | test.cpp:102:10:102:10 | x | test.cpp:98:10:98:13 | call to rand | test.cpp:102:10:102:10 | x | This arithmetic expression depends on an $@, potentially causing an overflow. | test.cpp:98:10:98:13 | call to rand | uncontrolled value |
 | test.cpp:146:9:146:9 | y | test.cpp:137:10:137:13 | call to rand | test.cpp:146:9:146:9 | y | This arithmetic expression depends on an $@, potentially causing an overflow. | test.cpp:137:10:137:13 | call to rand | uncontrolled value |

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

@@ -62,7 +62,7 @@ unsigned int test_remainder_subtract_unsigned()
 	unsigned int x = rand();
 	unsigned int y = x % 100; // y <= x
 
-	return x - y; // GOOD (as y <= x)
+	return x - y; // GOOD (as y <= x) [FALSE POSITIVE]
 }
 
 typedef unsigned long size_t;