stdio-common: Add test for vfscanf with matches longer than INT_MAX [BZ #27650]

Complement commit b03e4d7bd2 ("stdio: fix vfscanf with matches longer
than INT_MAX (bug 27650)") and add a test case for the issue, inspired
by the reproducer provided with the bug report.

This has been verified to succeed as from the commit referred and fail
beforehand.

As the test requires 2GiB of data to be passed around its performance
has been evaluated using a choice of systems and the execution time
determined to be respectively in the range of 9s for POWER9@2.166GHz,
24s for FU740@1.2GHz, and 40s for 74Kf@950MHz.  As this is on the verge
of and beyond the default timeout it has been increased by the factor of
8.  Regardless, following recent practice the test has been added to the
standard rather than extended set.

Reviewed-by: DJ Delorie <dj@redhat.com>

stdio-common/Makefile

@@ -240,6 +240,7 @@ tests := \
   tst-scanf-binary-c23 \
   tst-scanf-binary-gnu11 \
   tst-scanf-binary-gnu89 \
+  tst-scanf-bz27650 \
   tst-scanf-intn \
   tst-scanf-round \
   tst-scanf-to_inpunct \
@@ -328,6 +329,7 @@ generated += \
   tst-printf-fp-free.mtrace \
   tst-printf-fp-leak-mem.out \
   tst-printf-fp-leak.mtrace \
+  tst-scanf-bz27650.mtrace \
   tst-vfprintf-width-prec-mem.out \
   tst-vfprintf-width-prec.mtrace \
   # generated
@@ -419,6 +421,9 @@ tst-printf-fp-free-ENV = \
 tst-printf-fp-leak-ENV = \
   MALLOC_TRACE=$(objpfx)tst-printf-fp-leak.mtrace \
   LD_PRELOAD=$(common-objpfx)/malloc/libc_malloc_debug.so
+tst-scanf-bz27650-ENV = \
+  MALLOC_TRACE=$(objpfx)tst-scanf-bz27650.mtrace \
+  LD_PRELOAD=$(common-objpfx)malloc/libc_malloc_debug.so
 
 $(objpfx)tst-unbputc.out: tst-unbputc.sh $(objpfx)tst-unbputc
 	$(SHELL) $< $(common-objpfx) '$(test-program-prefix)'; \

stdio-common/tst-scanf-bz27650.c

@@ -0,0 +1,108 @@
+/* Test for BZ #27650, formatted input matching beyond INT_MAX.
+   Copyright (C) 2024 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 <error.h>
+#include <errno.h>
+#include <limits.h>
+#include <mcheck.h>
+#include <stddef.h>
+#include <stdio.h>
+#include <stdlib.h>
+#include <string.h>
+
+#include <sys/types.h>
+
+#include <support/check.h>
+#include <support/test-driver.h>
+
+/* Produce a stream of more than INT_MAX characters via buffer BUF of
+   size SIZE according to bookkeeping in COOKIE and then return EOF.  */
+
+static ssize_t
+io_read (void *cookie, char *buf, size_t size)
+{
+  unsigned int *written = cookie;
+  unsigned int w = *written;
+
+  if (w > INT_MAX)
+    return 0;
+
+  memset (buf, 'a', size);
+  *written = w + size;
+  return size;
+}
+
+/* Consume a stream of more than INT_MAX characters from an artificial
+   input stream of which none is the new line character.  The call to
+   fscanf is supposed to complete upon the EOF condition of input,
+   however in the presence of BZ #27650 it will terminate prematurely
+   with characters still outstanding in input.  Diagnose the condition
+   and return status accordingly.  */
+
+int
+do_test (void)
+{
+  static cookie_io_functions_t io_funcs = { .read = io_read };
+  unsigned int written = 0;
+  FILE *in;
+  int v;
+
+  mtrace ();
+
+  in = fopencookie (&written, "r", io_funcs);
+  if (in == NULL)
+    {
+      FAIL ("fopencookie: %m");
+      goto out;
+    }
+
+  v = fscanf (in, "%*[^\n]");
+  if (ferror (in))
+    {
+      FAIL ("fscanf: input failure, at %u: %m", written);
+      goto out_close;
+    }
+  else if (v == EOF)
+    {
+      FAIL ("fscanf: unexpected end of file, at %u", written);
+      goto out_close;
+    }
+
+  if (!feof (in))
+    {
+      v = fgetc (in);
+      if (ferror (in))
+	FAIL ("fgetc: input failure: %m");
+      else if (v == EOF)
+	FAIL ("fgetc: unexpected end of file after missing end of file");
+      else if (v == '\n')
+	FAIL ("unexpected new line character received");
+      else
+	FAIL ("character received after end of file expected: \\x%02x", v);
+    }
+
+out_close:
+  if (fclose (in) != 0)
+    FAIL ("fclose: %m");
+
+out:
+  return EXIT_SUCCESS;
+}
+
+#define TIMEOUT (DEFAULT_TIMEOUT * 8)
+#include <support/test-driver.c>