codeql/change-notes/1.19/analysis-cpp.md

Improvements to C/C++ analysis

General improvements

New queries

Query	Tags	Purpose
Cast between HRESULT and a Boolean type (cpp/hresult-boolean-conversion)	external/cwe/cwe-253	Finds logic errors caused by mistakenly treating the Windows HRESULT type as a Boolean instead of testing it with the appropriate macros. Enabled by default.
Setting a DACL to NULL in a SECURITY_DESCRIPTOR (cpp/unsafe-dacl-security-descriptor)	external/cwe/cwe-732	This query finds code that creates world-writable objects on Windows by setting their DACL to NULL. Enabled by default.
Cast from char* to wchar_t*	security, external/cwe/cwe-704	Detects potentially dangerous casts from char* to wchar_t*. Enabled by default on LGTM.
Dead code due to goto or break statement (cpp/dead-code-goto)	maintainability, external/cwe/cwe-561	Detects dead code following a goto or break statement. Enabled by default on LGTM.

Changes to existing queries

Query	Expected impact	Change
Empty branch of conditional	Fewer false positive results	The query now recognizes commented blocks more reliably.
Expression has no effect	Fewer false positive results	Expressions in template instantiations are now excluded from this query.
Resource not released in destructor	Fewer false positive results	Placement new is now excluded from the query. Also fixed an issue where false positives could occur if the destructor body was not in the snapshot.
Missing return statement (cpp/missing-return)	Visible by default	The precision of this query has been increased from 'medium' to 'high', which makes it visible by default in LGTM. It was 'medium' in release 1.17 and 1.18 because it had false positives due to an extractor bug that was fixed in 1.18.
Missing return statement	Fewer false positive results	The query is now produces correct results when a function returns a template-dependent type.
Call to memory access function may overflow buffer	More correct results	Array indexing with a negative index is now detected by this query.
Suspicious call to memset	Fewer false positive results	Types involving decltype are now correctly compared.
Suspicious add with sizeof	Fewer false positive results	Arithmetic with void pointers (where allowed) is now excluded from this query.
Wrong type of arguments to formatting function	Fewer false positive results	False positive results involving typedefs have been removed. Expected argument types are determined more accurately, especially for wide string and pointer types. Custom (non-standard) formatting functions are also identified more accurately.

Changes to QL libraries

• Added a hash consing library for structural comparison of expressions.
• getBufferSize now detects variable size structs more reliably.
• Buffer.qll now treats arrays of zero size as a special case.