[Bug libstdc++/51772] New: --enable-clocale=generic makes unsafe assumptions about ctype_base::mask

[redi at gcc dot gnu.org]

http://gcc.gnu.org/bugzilla/show_bug.cgi?id=51772

             Bug #: 51772
           Summary: --enable-clocale=generic makes unsafe assumptions
                    about ctype_base::mask
    Classification: Unclassified
           Product: gcc
           Version: 4.7.0
            Status: UNCONFIRMED
          Severity: normal
          Priority: P3
         Component: libstdc++
        AssignedTo: unassigned@gcc.gnu.org
        ReportedBy: redi@gcc.gnu.org
            Blocks: 51018


config/locale/generic/ctype_members.cc initializes _M_bit like so:

    for (size_t __i = 0; __i <= 15; ++__i)
      {
        _M_bit[__i] = static_cast<mask>(1 << __i);
        _M_wmask[__i] = _M_convert_to_wmask(_M_bit[__i]);
      }

This assumes that ctype_base::mask is at least 16 bits.

Each element of _M_bit has a single bit set, and is compared to the defined
mask constants in _M_convert_to_wmask:

  ctype<wchar_t>::__wmask_type
  ctype<wchar_t>::_M_convert_to_wmask(const mask __m) const throw()
  {
    __wmask_type __ret;
    switch (__m)
      {
      // ...
      case xdigit:
        __ret = wctype("xdigit");
        break;
      case alnum:
        __ret = wctype("alnum");
        break;
      case graph:
        __ret = wctype("graph");
        break;
      default:
        __ret = __wmask_type();
      }
    return __ret;
  };

If any of the mask constants has more than one bit set it will never be
matched.

e.g. on NetBSD xdigit can never be matched for ctype<wchar_t> because
config/os/bsd/netbsd/ctype_base.h defines the following

    typedef unsigned char       mask;

    static const mask xdigit    = _N | _X;

As a result, this valid program aborts:

#include <locale>
#include <assert.h>

class gnu_ctype: public std::ctype<wchar_t> { };

int main()
{
  gnu_ctype gctype;

  assert(gctype.is(std::ctype_base::xdigit, L'a'));
}