C++: Fix an issue with cpp/suspicious-add-sizeof in BMN databases

cpp/ql/src/Security/CWE/CWE-468/SuspiciousAddWithSizeof.ql

@@ -18,7 +18,8 @@ import IncorrectPointerScalingCommon
 private predicate isCharSzPtrExpr(Expr e) {
   exists(PointerType pt | pt = e.getFullyConverted().getUnspecifiedType() |
     pt.getBaseType() instanceof CharType or
-    pt.getBaseType() instanceof VoidType
+    pt.getBaseType() instanceof VoidType or
+    pt.getBaseType() instanceof ErroneousType // this could be char / void type in a successful compilation
   )
 }
 

cpp/ql/src/change-notes/2026-03-19-suspicious-add-sizeof.md

@@ -0,0 +1,4 @@
+---
+category: minorAnalysis
+---
+* Fixed an issue with the "Suspicious add with sizeof" (`cpp/suspicious-add-sizeof`) query causing false positive results in `build-mode: none` databases.

cpp/ql/test/query-tests/Security/CWE/CWE-468/semmle/SuspiciousAddWithSizeof/SuspiciousAddWithSizeof.expected

@@ -1,3 +1,5 @@
+| buildless.cpp:5:15:5:25 | sizeof(int) | Suspicious sizeof offset in a pointer arithmetic expression. The type of the pointer is $@. | file://:0:0:0:0 | const short * | const short * |
+| buildless.cpp:6:13:6:23 | sizeof(int) | Suspicious sizeof offset in a pointer arithmetic expression. The type of the pointer is $@. | file://:0:0:0:0 | const int * | const int * |
 | test.cpp:6:30:6:40 | sizeof(int) | Suspicious sizeof offset in a pointer arithmetic expression. The type of the pointer is $@. | file://:0:0:0:0 | int * | int * |
 | test.cpp:14:30:14:40 | sizeof(int) | Suspicious sizeof offset in a pointer arithmetic expression. The type of the pointer is $@. | file://:0:0:0:0 | int * | int * |
 | test.cpp:22:25:22:35 | sizeof(int) | Suspicious sizeof offset in a pointer arithmetic expression. The type of the pointer is $@. | file://:0:0:0:0 | int * | int * |

cpp/ql/test/query-tests/Security/CWE/CWE-468/semmle/SuspiciousAddWithSizeof/buildless.cpp

@@ -0,0 +1,10 @@
+// semmle-extractor-options: --expect_errors
+
+void test_buildless(const char *p_c, const short *p_short, const int *p_int, const uint8_t *p_8, const uint16_t *p_16, const uint32_t *p_32) {
+  *(p_c + sizeof(int)); // GOOD (`sizeof(char)` is 1)
+  *(p_short + sizeof(int)); // BAD
+  *(p_int + sizeof(int)); // BAD
+  *(p_8 + sizeof(int)); // GOOD (`sizeof(uint8_t)` is 1, but there's an error in the type)
+  *(p_16 + sizeof(int)); // BAD [NOT DETECTED]
+  *(p_32 + sizeof(int)); // BAD [NOT DETECTED]
+}

cpp/ql/test/query-tests/Security/CWE/CWE-468/semmle/SuspiciousAddWithSizeof/test.cpp

@@ -93,3 +93,9 @@ class MyTest8Class
   myChar * const myCharsPointer;
   myInt * const myIntsPointer;
 };
+
+typedef unsigned char uint8_t;
+typedef unsigned short uint16_t;
+typedef unsigned int uint32_t;
+
+void test_buildless(const char *p_c, const short *p_short, const int *p_int, const uint8_t *p_8, const uint16_t *p_16, const uint32_t *p_32);