[PATCH 2/2] wcsmbs: Add gconv module ref counter overflow test

[Adhemerval Zanella Netto]

On 29/04/26 11:59, Frédéric Bérat wrote:
> Adds a new xtest, tst-wcsmbs-clone-overflow, to detect reference count
> leaks in gconv modules.
> 
> The test specifically targets an issue where functions like swscanf
> trigger __wcsmbs_clone_conv without a corresponding release when
> processing wide character strings from stack-allocated buffers. This
> results in a leaked reference count for the gconv module.
> 
> The test performs 0x80000000 iterations to ensure a 32-bit signed
> integer reference counter overflows, thus reliably reproducing and
> verifying the leak. It is marked as an xtest due to its long runtime.
> 
> Assisted-by: LLM

I usually see xtests are not that useful, they are not actively tested 
and usually require some specific configuration to run (like some kernel
support).  And requiring 3-5 minutes on a recent chip does not really
help the test-suite, which requires a lot of time already.

Maybe you can make it an unit test / internal test that calls 
__vfwscanf_internal / _IO_wstrfile_fclose_stack and checks the counter
value directly.

> ---
>  wcsmbs/Makefile                    |  3 +-
>  wcsmbs/tst-wcsmbs-clone-overflow.c | 50 ++++++++++++++++++++++++++++++
>  2 files changed, 52 insertions(+), 1 deletion(-)
>  create mode 100644 wcsmbs/tst-wcsmbs-clone-overflow.c
> 
> diff --git a/wcsmbs/Makefile b/wcsmbs/Makefile
> index 849a47971e..e9db577220 100644
> --- a/wcsmbs/Makefile
> +++ b/wcsmbs/Makefile
> @@ -208,7 +208,7 @@ tests := \
>    # tests
>  
>  # This test runs for a long time.
> -xtests += test-wcsncmp-nonarray
> +xtests += test-wcsncmp-nonarray tst-wcsmbs-clone-overflow

It should be

xtests += \
  test-wcsncmp-nonarray \
  tst-wcsmbs-clone-overflow \
  # xtest

>  
>  
>  include ../Rules
> @@ -241,6 +241,7 @@ $(objpfx)tst-c32-state.out: $(gen-locales)
>  $(objpfx)test-c8rtomb.out: $(gen-locales)
>  $(objpfx)test-mbrtoc8.out: $(gen-locales)
>  $(objpfx)tst-wscanf-to_inpunct.out: $(gen-locales)
> +$(objpfx)tst-wcsmbs-clone-overflow.out: $(gen-locales)
>  endif
>  
>  $(objpfx)tst-wcstod-round: $(libm)
> diff --git a/wcsmbs/tst-wcsmbs-clone-overflow.c b/wcsmbs/tst-wcsmbs-clone-overflow.c
> new file mode 100644
> index 0000000000..a6f0a25685
> --- /dev/null
> +++ b/wcsmbs/tst-wcsmbs-clone-overflow.c
> @@ -0,0 +1,50 @@
> +/* Test for gconv module reference counter overflow.
> +   Copyright (C) 2026 Free Software Foundation, Inc.
> +   This file is part of the GNU C Library.
> +
> +   The GNU C Library is free software; you can redistribute it and/or
> +   modify it under the terms of the GNU Lesser General Public
> +   License as published by the Free Software Foundation; either
> +   version 2.1 of the License, or (at your option) any later version.
> +
> +   The GNU C Library is distributed in the hope that it will be useful,
> +   but WITHOUT ANY WARRANTY; without even the implied warranty of
> +   MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the GNU
> +   Lesser General Public License for more details.
> +
> +   You should have received a copy of the GNU Lesser General Public
> +   License along with the GNU C Library; if not, see
> +   <https://www.gnu.org/licenses/>.  */
> +
> +#include <stdio.h>
> +#include <wchar.h>
> +#include <locale.h>
> +#include <support/check.h>
> +#include <support/support.h>
> +
> +static int
> +do_test (int argc, char **argv)
> +{
> +  if (setlocale (LC_ALL, "de_DE.ISO-8859-1") == NULL)
> +    FAIL_EXIT1 ("setlocale failed, check if de_DE.ISO-8859-1 is generated");
> +
> +  /* The reproduction loop. 0x80000000 iterations are required to overflow
> +     a 32-bit signed integer. This typically takes 3-5 minutes.  */
> +  wchar_t buf[32] = L"123";
> +  int j;
> +  for (long long i = 0; i < 0x80000000LL; i++)
> +    {
> +      /* swscanf on a stack-allocated buffer triggers __wcsmbs_clone_conv
> +         without a corresponding release, leaking a reference count.  */
> +      if (swscanf (buf, L"%d", &j) < 1)
> +        FAIL_EXIT1 ("swscanf failed at iteration %lld", i);
> +      /* Prevent compiler from optimizing the loop away. */
> +      __asm__ volatile ("" : : "g" (j) : "memory");
> +    }
> +
> +  return 0;
> +}
> +
> +/* This test is slow because it requires billions of iterations.  */
> +#define TIMEOUT 600
> +#include "../test-skeleton.c"

#include <support/test-driver.c>