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From: "redi at gcc dot gnu.org" <gcc-bugzilla@gcc.gnu.org>
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Subject: [Bug libstdc++/102592] [11/12 Regression] heap-use-after-free when
 constructing std::filesystem::path from iterator pair
Date: Mon, 04 Oct 2021 13:22:08 +0000
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https://gcc.gnu.org/bugzilla/show_bug.cgi?id=3D102592

Jonathan Wakely <redi at gcc dot gnu.org> changed:

           What    |Removed                     |Added
----------------------------------------------------------------------------
            Summary|heap-use-after-free when    |[11/12 Regression]
                   |constructing                |heap-use-after-free when
                   |std::filesystem::path from  |constructing
                   |iterator pair               |std::filesystem::path from
                   |                            |iterator pair
     Ever confirmed|0                           |1
           Assignee|unassigned at gcc dot gnu.org      |redi at gcc dot gnu=
.org
           Keywords|                            |wrong-code
   Last reconfirmed|                            |2021-10-04
      Known to work|                            |10.3.1
             Status|UNCONFIRMED                 |ASSIGNED
      Known to fail|                            |11.2.1, 12.0

--- Comment #1 from Jonathan Wakely <redi at gcc dot gnu.org> ---
The problem is the last line of this function:

    template<typename _Tp>
      static auto
      _S_convert(const _Tp& __str)
      {
        if constexpr (is_same_v<_Tp, string_type>)
          return __str;
        else if constexpr (is_same_v<_Tp, basic_string_view<value_type>>)
          return __str;
        else if constexpr (is_same_v<typename _Tp::value_type, value_type>)
          return basic_string_view<value_type>(__str.data(), __str.size());
        else
          return _S_convert(__str.data(), __str.data() + __str.size());
      }

That returns a basic_string_view<char8_t> referring to the contents of __st=
r,
but that is an rvalue basic_string<char8_t> that goes out of scope before t=
he
result is used.=