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libstdc++: Fix use-after-free in std::format [PR119671]

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When formatting floating-point values to wide strings there's a case
where we invalidate a std::wstring buffer while a std::wstring_view is
still referring to it.

libstdc++-v3/ChangeLog:

	PR libstdc++/119671
	* include/std/format (__formatter_fp::format): Do not invalidate
	__wstr unless _M_localized returns a valid string.
	* testsuite/std/format/functions/format.cc: Check wide string
	formatting of floating-point types with classic locale.

Reviewed-by: Tomasz Kaminski <tkaminsk@redhat.com>
This commit is contained in:
Jonathan Wakely 2025-04-07 19:52:55 +01:00 • committed by Jonathan Wakely
parent a9bbb60b7c
commit e33b62eed7
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2 changed files with 15 additions and 3 deletions
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6
libstdc++-v3/include/std/format
View file

@ -1838,9 +1838,9 @@ namespace __format
if (_M_spec._M_localized && __builtin_isfinite(__v))
{
__wstr = _M_localize(__str, __expc, __fc.locale());
if (!__wstr.empty())
__str = __wstr;
auto __s = _M_localize(__str, __expc, __fc.locale());
if (!__s.empty())
__str = __wstr = std::move(__s);
}
size_t __width = _M_spec._M_get_width(__fc);

12
libstdc++-v3/testsuite/std/format/functions/format.cc
View file

@ -370,6 +370,18 @@ test_wchar()
// P2909R4 Fix formatting of code units as integers (Dude, where’s my char?)
s = std::format(L"{:d} {:d}", wchar_t(-1), char(-1));
VERIFY( s.find('-') == std::wstring::npos );
auto ws = std::format(L"{:L}", 0.5);
VERIFY( ws == L"0.5" );
// The default C locale.
std::locale cloc = std::locale::classic();
// PR libstdc++/119671 use-after-free formatting floating-point to wstring
ws = std::format(cloc, L"{:L}", 0.5);
VERIFY( ws == L"0.5" );
// A locale with no name, but with the same facets as the C locale.
std::locale locx(cloc, &std::use_facet<std::ctype<char>>(cloc));
ws = std::format(locx, L"{:L}", 0.5);
VERIFY( ws == L"0.5" );
}
void