assert: Add test for CVE-2025-0395

Use the __progname symbol to override the program name to induce the
failure that CVE-2025-0395 describes.

This is related to BZ #32582

Signed-off-by: Siddhesh Poyarekar <siddhesh@sourceware.org>
Reviewed-by: Adhemerval Zanella  <adhemerval.zanella@linaro.org>

assert/Makefile

@@ -39,6 +39,7 @@ tests := \
   test-assert-perr \
   tst-assert-c++ \
   tst-assert-g++ \
+  tst-assert-sa-2025-0001 \
   # tests
 
 ifeq ($(have-cxx-thread_local),yes)

assert/tst-assert-sa-2025-0001.c

@@ -0,0 +1,92 @@
+/* Test for CVE-2025-0395.
+   Copyright The GNU Toolchain Authors.
+   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/>.  */
+
+/* Test that a large enough __progname does not result in a buffer overflow
+   when printing an assertion failure.  This was CVE-2025-0395.  */
+#include <assert.h>
+#include <inttypes.h>
+#include <signal.h>
+#include <stdbool.h>
+#include <string.h>
+#include <sys/mman.h>
+#include <support/check.h>
+#include <support/support.h>
+#include <support/xstdio.h>
+#include <support/xunistd.h>
+
+extern const char *__progname;
+
+int
+do_test (int argc, char **argv)
+{
+
+  support_need_proc ("Reads /proc/self/maps to add guards to writable maps.");
+  ignore_stderr ();
+
+  /* XXX assumes that the assert is on a 2 digit line number.  */
+  const char *prompt = ": %s:99: do_test: Assertion `argc < 1' failed.\n";
+
+  int ret = fprintf (stderr, prompt, __FILE__);
+  if (ret < 0)
+    FAIL_EXIT1 ("fprintf failed: %m\n");
+
+  size_t pagesize = getpagesize ();
+  size_t namesize = pagesize - 1 - ret;
+
+  /* Alter the progname so that the assert message fills the entire page.  */
+  char progname[namesize];
+  memset (progname, 'A', namesize - 1);
+  progname[namesize - 1] = '\0';
+  __progname = progname;
+
+  FILE *f = xfopen ("/proc/self/maps", "r");
+  char *line = NULL;
+  size_t len = 0;
+  uintptr_t prev_to = 0;
+
+  /* Pad the beginning of every writable mapping with a PROT_NONE map.  This
+     ensures that the mmap in the assert_fail path never ends up below a
+     writable map and will terminate immediately in case of a buffer
+     overflow.  */
+  while (xgetline (&line, &len, f))
+    {
+      uintptr_t from, to;
+      char perm[4];
+
+      sscanf (line, "%" SCNxPTR "-%" SCNxPTR " %c%c%c%c ",
+	      &from, &to,
+	      &perm[0], &perm[1], &perm[2], &perm[3]);
+
+      bool writable = (memchr (perm, 'w', 4) != NULL);
+
+      if (prev_to != 0 && from - prev_to > pagesize && writable)
+	xmmap ((void *) from - pagesize, pagesize, PROT_NONE,
+	       MAP_ANONYMOUS | MAP_PRIVATE, 0);
+
+      prev_to = to;
+    }
+
+  xfclose (f);
+
+  assert (argc < 1);
+  return 0;
+}
+
+#define EXPECTED_SIGNAL SIGABRT
+#define TEST_FUNCTION_ARGV do_test
+#include <support/test-driver.c>