From 789c57bc5fe023fc6dc72ade4afcb0916ff788d3 Mon Sep 17 00:00:00 2001 From: Jonathan Wakely Date: Tue, 4 May 2021 15:49:38 +0100 Subject: [PATCH] libstdc++: Fix undefined behaviour in std::string This fixes a ubsan error when constructing a string with a null pointer: bits/basic_string.h:534:21: runtime error: applying non-zero offset 18446744073709551615 to null pointer The _M_construct function only cares whether the second pointer is non-null, so create a non-null value without undefined arithmetic. We can also pass the random_access_iterator_tag directly to the _M_construct function, to avoid going via the tag dispatching _M_construct_aux, because we know we have pointers not integers here. libstdc++-v3/ChangeLog: * include/bits/basic_string.h (basic_string(const CharT*, const A&)): Do not do arithmetic on null pointer. --- libstdc++-v3/include/bits/basic_string.h | 7 ++++++- 1 file changed, 6 insertions(+), 1 deletion(-) diff --git a/libstdc++-v3/include/bits/basic_string.h b/libstdc++-v3/include/bits/basic_string.h index fba7c6f..84356ad 100644 --- a/libstdc++-v3/include/bits/basic_string.h +++ b/libstdc++-v3/include/bits/basic_string.h @@ -531,7 +531,12 @@ _GLIBCXX_BEGIN_NAMESPACE_CXX11 #endif basic_string(const _CharT* __s, const _Alloc& __a = _Alloc()) : _M_dataplus(_M_local_data(), __a) - { _M_construct(__s, __s ? __s + traits_type::length(__s) : __s+npos); } + { + const _CharT* __end = __s ? __s + traits_type::length(__s) + // We just need a non-null pointer here to get an exception: + : reinterpret_cast(__alignof__(_CharT)); + _M_construct(__s, __end, random_access_iterator_tag()); + } /** * @brief Construct string as multiple characters. -- 2.7.4