nsswitch: do not reload if "/" changes

https://sourceware.org/bugzilla/show_bug.cgi?id=27077

Before reloading nsswitch.conf, verify that the root directory
hasn't changed - if it has, it's likely that we've entered a
container and should not trust the nsswitch inside the container
nor load any shared objects therein.

Reviewed-by: Carlos O'Donell <carlos@redhat.com>

1 files changed, 126 insertions, 0 deletions

diff --git a/nss/tst-reload2.c b/nss/tst-reload2.c
new file mode 100644
index 0000000..128db25
--- /dev/null
+++ b/nss/tst-reload2.c
@@ -0,0 +1,126 @@
+/* Test that reloading is disabled after a chroot.
+   Copyright (C) 2020-2021 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 <nss.h>
+#include <stdio.h>
+#include <stdlib.h>
+#include <string.h>
+#include <limits.h>
+#include <sys/types.h>
+#include <errno.h>
+#include <pwd.h>
+#include <grp.h>
+#include <unistd.h>
+
+#include <support/support.h>
+#include <support/check.h>
+#include <support/xunistd.h>
+
+#include "nss_test.h"
+
+static struct passwd pwd_table1[] =
+  {
+   PWD_N (1234, "test1"),
+   PWD_N (4321, "test2"),
+   PWD_LAST ()
+  };
+
+static const char *group_4[] = {
+  "alpha", "beta", "gamma", "fred", NULL
+};
+
+static struct group group_table_data[] =
+  {
+   GRP (4),
+   GRP_LAST ()
+  };
+
+void
+_nss_test1_init_hook (test_tables *t)
+{
+  t->pwd_table = pwd_table1;
+  t->grp_table = group_table_data;
+}
+
+static struct passwd pwd_table2[] =
+  {
+   PWD_N (5, "test1"),
+   PWD_N (2468, "test2"),
+   PWD_LAST ()
+  };
+
+void
+_nss_test2_init_hook (test_tables *t)
+{
+  t->pwd_table = pwd_table2;
+}
+
+static int
+do_test (void)
+{
+  struct passwd *pw;
+  struct group *gr;
+  char buf1[PATH_MAX];
+  char buf2[PATH_MAX];
+
+  sprintf (buf1, "/subdir%s", support_slibdir_prefix);
+  xmkdirp (buf1, 0777);
+
+  /* Copy this DSO into the chroot so it *could* be loaded.  */
+  sprintf (buf1, "%s/libnss_files.so.2", support_slibdir_prefix);
+  sprintf (buf2, "/subdir%s/libnss_files.so.2", support_slibdir_prefix);
+  support_copy_file (buf1, buf2);
+
+  /* Check we're using the "outer" nsswitch.conf.  */
+
+  /* This uses the test1 DSO.  */
+  pw = getpwnam ("test1");
+  TEST_VERIFY (pw != NULL);
+  if (pw)
+    TEST_COMPARE (pw->pw_uid, 1234);
+
+  /* This just loads the test2 DSO.  */
+  gr = getgrnam ("name4");
+
+  /* Change the root dir.  */
+
+  TEST_VERIFY (chroot ("/subdir") == 0);
+  chdir ("/");
+
+  /* Check we're NOT using the "inner" nsswitch.conf.  */
+
+  /* Both DSOs are loaded, which is used?  */
+  pw = getpwnam ("test2");
+  TEST_VERIFY (pw != NULL);
+  if (pw)
+    TEST_VERIFY (pw->pw_uid != 2468);
+
+  /* The "files" DSO should not be loaded.  */
+  gr = getgrnam ("test3");
+  TEST_VERIFY (gr == NULL);
+
+  /* We should still be using the old configuration.  */
+  pw = getpwnam ("test1");
+  TEST_VERIFY (pw != NULL);
+  if (pw)
+    TEST_COMPARE (pw->pw_uid, 1234);
+
+  return 0;
+}
+
+#include <support/test-driver.c>