[gcc r12-7690] libstdc++: Rewrite __moneypunct_cache::_M_cache [PR104966]

[Jonathan Wakely <redi@gcc.gnu.org>]

https://gcc.gnu.org/g:38ce4489635f2d65de965af3ec5d5c4adf7762d9

commit r12-7690-g38ce4489635f2d65de965af3ec5d5c4adf7762d9
Author: Jonathan Wakely <jwakely@redhat.com>
Date:   Thu Mar 17 13:33:07 2022 +0000

    libstdc++: Rewrite __moneypunct_cache::_M_cache [PR104966]
    
    GCC thinks the following can lead to a buffer overflow when __ns.size()
    equals zero:
    
              const basic_string<_CharT>& __ns = __mp.negative_sign();
              _M_negative_sign_size = __ns.size();
              __negative_sign = new _CharT[_M_negative_sign_size];
              __ns.copy(__negative_sign, _M_negative_sign_size);
    
    This happens because operator new might be replaced with something that
    writes to this->_M_negative_sign_size and so the basic_string::copy call
    could use a non-zero size to write to a zero-length buffer.
    
    The solution suggested by Richi is to cache the size in a local variable
    so that the compiler knows it won't be changed between the allocation
    and the copy.
    
    This commit goes further and rewrites the whole function to use RAII and
    delay all modifications of *this until after all allocations have
    succeeded. The RAII helper type caches the size and copies the string
    and owns the memory until told to release it.
    
    libstdc++-v3/ChangeLog:
    
            PR middle-end/104966
            * include/bits/locale_facets_nonio.tcc
            (__moneypunct_cache::_M_cache): Replace try-catch with RAII and
            make all string copies before any stores to *this.

Diff:
---
 libstdc++-v3/include/bits/locale_facets_nonio.tcc | 102 +++++++++++-----------
 1 file changed, 51 insertions(+), 51 deletions(-)

diff --git a/libstdc++-v3/include/bits/locale_facets_nonio.tcc b/libstdc++-v3/include/bits/locale_facets_nonio.tcc
index 98442418f51..8c37a706db8 100644
--- a/libstdc++-v3/include/bits/locale_facets_nonio.tcc
+++ b/libstdc++-v3/include/bits/locale_facets_nonio.tcc
@@ -71,61 +71,61 @@ _GLIBCXX_BEGIN_NAMESPACE_VERSION
       const moneypunct<_CharT, _Intl>& __mp =
 	use_facet<moneypunct<_CharT, _Intl> >(__loc);
 
+      struct _Scoped_str
+      {
+	size_t _M_len;
+	_CharT* _M_str;
+
+	explicit
+	_Scoped_str(const basic_string<_CharT>& __str)
+	: _M_len(__str.size()), _M_str(new _CharT[_M_len])
+	{ __str.copy(_M_str, _M_len); }
+
+	~_Scoped_str() { delete[] _M_str; }
+
+	void
+	_M_release(const _CharT*& __p, size_t& __n)
+	{
+	  __p = _M_str;
+	  __n = _M_len;
+	  _M_str = 0;
+	}
+      };
+
+      _Scoped_str __curr_symbol(__mp.curr_symbol());
+      _Scoped_str __positive_sign(__mp.positive_sign());
+      _Scoped_str __negative_sign(__mp.negative_sign());
+
+      const string& __g = __mp.grouping();
+      const size_t __g_size = __g.size();
+      char* const __grouping = new char[__g_size];
+      __g.copy(__grouping, __g_size);
+
+      // All allocations succeeded without throwing, OK to modify *this now.
+
+      _M_grouping = __grouping;
+      _M_grouping_size = __g_size;
+      _M_use_grouping = (__g_size
+			 && static_cast<signed char>(__grouping[0]) > 0
+			 && (__grouping[0]
+			     != __gnu_cxx::__numeric_traits<char>::__max));
+
       _M_decimal_point = __mp.decimal_point();
       _M_thousands_sep = __mp.thousands_sep();
+
+      __curr_symbol._M_release(_M_curr_symbol, _M_curr_symbol_size);
+      __positive_sign._M_release(_M_positive_sign, _M_positive_sign_size);
+      __negative_sign._M_release(_M_negative_sign, _M_negative_sign_size);
+
       _M_frac_digits = __mp.frac_digits();
+      _M_pos_format = __mp.pos_format();
+      _M_neg_format = __mp.neg_format();
 
-      char* __grouping = 0;
-      _CharT* __curr_symbol = 0;
-      _CharT* __positive_sign = 0;
-      _CharT* __negative_sign = 0;     
-      __try
-	{
-	  const string& __g = __mp.grouping();
-	  _M_grouping_size = __g.size();
-	  __grouping = new char[_M_grouping_size];
-	  __g.copy(__grouping, _M_grouping_size);
-	  _M_use_grouping = (_M_grouping_size
-			     && static_cast<signed char>(__grouping[0]) > 0
-			     && (__grouping[0]
-				 != __gnu_cxx::__numeric_traits<char>::__max));
-
-	  const basic_string<_CharT>& __cs = __mp.curr_symbol();
-	  _M_curr_symbol_size = __cs.size();
-	  __curr_symbol = new _CharT[_M_curr_symbol_size];
-	  __cs.copy(__curr_symbol, _M_curr_symbol_size);
-
-	  const basic_string<_CharT>& __ps = __mp.positive_sign();
-	  _M_positive_sign_size = __ps.size();
-	  __positive_sign = new _CharT[_M_positive_sign_size];
-	  __ps.copy(__positive_sign, _M_positive_sign_size);
-
-	  const basic_string<_CharT>& __ns = __mp.negative_sign();
-	  _M_negative_sign_size = __ns.size();
-	  __negative_sign = new _CharT[_M_negative_sign_size];
-	  __ns.copy(__negative_sign, _M_negative_sign_size);
-
-	  _M_pos_format = __mp.pos_format();
-	  _M_neg_format = __mp.neg_format();
-
-	  const ctype<_CharT>& __ct = use_facet<ctype<_CharT> >(__loc);
-	  __ct.widen(money_base::_S_atoms,
-		     money_base::_S_atoms + money_base::_S_end, _M_atoms);
-
-	  _M_grouping = __grouping;
-	  _M_curr_symbol = __curr_symbol;
-	  _M_positive_sign = __positive_sign;
-	  _M_negative_sign = __negative_sign;
-	  _M_allocated = true;
-	}
-      __catch(...)
-	{
-	  delete [] __grouping;
-	  delete [] __curr_symbol;
-	  delete [] __positive_sign;
-	  delete [] __negative_sign;
-	  __throw_exception_again;
-	}
+      const ctype<_CharT>& __ct = use_facet<ctype<_CharT> >(__loc);
+      __ct.widen(money_base::_S_atoms,
+		 money_base::_S_atoms + money_base::_S_end, _M_atoms);
+
+      _M_allocated = true;
     }
 
 _GLIBCXX_BEGIN_NAMESPACE_LDBL_OR_CXX11