test: Add gconv refcount leak test for swscanf

Add a new internal test, `tst-wcsmbs-clone-overflow`, to verify correct
gconv module reference counting. The Makefile is updated to include this
test in the `tests-internal` list and ensure it runs with generated locales.

This test specifically checks that the `__counter` for `gconv_fcts->towc`
does not leak references when `swscanf` is used with a stack-allocated
wide character stream. It ensures that `_IO_wstrfile_fclose_stack`
properly decrements the module reference counter, preventing a module
from staying loaded indefinitely due to unreleased references.

Assisted-by: LLM
Reviewed-by: Adhemerval Zanella  <adhemerval.zanella@linaro.org>

diff --git a/wcsmbs/Makefile b/wcsmbs/Makefile
index 849a47971e0a0278962c6564f30d4504819079b4..ee3638c0e59842b3b26138a8c1b1432b768a744a 100644 (file)
--- a/wcsmbs/Makefile
+++ b/wcsmbs/Makefile
@@ -210,6 +210,12 @@ tests := \
 # This test runs for a long time.
 xtests += test-wcsncmp-nonarray
 
+tests-internal += \
+  tst-wcsmbs-clone-overflow
+
+tests-static += \
+  tst-wcsmbs-clone-overflow
+
 
 include ../Rules
 
@@ -241,6 +247,7 @@ $(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 (file)
index 0000000..adfd4fa
--- /dev/null
+++ b/wcsmbs/tst-wcsmbs-clone-overflow.c
@@ -0,0 +1,66 @@
+/* Test for gconv module reference counter leak.
+   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 <locale.h>
+#include <stdio.h>
+#include <wchar.h>
+#include <support/check.h>
+#include <support/support.h>
+
+/* Internal headers for accessing the gconv structures.  */
+#include <locale/localeinfo.h>
+#include <iconv/gconv_int.h>
+#include <wcsmbs/wcsmbsload.h>
+
+static int
+do_test (void)
+{
+  if (setlocale (LC_ALL, "de_DE.ISO-8859-1") == NULL)
+    FAIL_EXIT1 ("setlocale failed, check if de_DE.ISO-8859-1 is generated");
+
+  wchar_t buf[32] = L"123";
+  int j;
+
+  /* First iteration initializes the gconv functions internally.  */
+  if (swscanf (buf, L"%d", &j) < 1)
+    FAIL_EXIT1 ("swscanf failed");
+
+  /* Retrieve the current gconv_fcts from the LC_CTYPE locale data.  */
+  struct __locale_data *loc = _NL_CURRENT_DATA (LC_CTYPE);
+  struct lc_ctype_data *ctype = loc->private;
+  const struct gconv_fcts *fcts = ctype->fcts;
+
+  TEST_VERIFY_EXIT (fcts != NULL);
+  TEST_VERIFY_EXIT (fcts->towc != NULL);
+
+  /* Capture the reference counter.  */
+  int initial_counter = fcts->towc->__counter;
+
+  /* Perform a second iteration of swscanf. If the stack-allocated FILE
+     leaks the gconv reference, the counter will increment.  */
+  if (swscanf (buf, L"%d", &j) < 1)
+    FAIL_EXIT1 ("swscanf failed");
+
+  /* The counter should be unchanged, as _IO_wstrfile_fclose_stack should
+     have decremented it correctly.  */
+  TEST_COMPARE (fcts->towc->__counter, initial_counter);
+
+  return 0;
+}
+
+#include <support/test-driver.c>