nss_db: fix endent wrt NULL mappings [BZ #24695] [BZ #24696]

nss_db allows for getpwent et al to be called without a set*ent,
but it only works once.  After the last get*ent a set*ent is
required to restart, because the end*ent did not properly reset
the module.  Resetting it to NULL allows for a proper restart.

If the database doesn't exist, however, end*ent erroniously called
munmap which set errno.

The test case runs "makedb" inside the testroot, so needs selinux
DSOs installed.

1 files changed, 54 insertions, 0 deletions

diff --git a/nss/tst-nss-db-endgrent.c b/nss/tst-nss-db-endgrent.c
new file mode 100644
index 0000000..367cc6c
--- /dev/null
+++ b/nss/tst-nss-db-endgrent.c
@@ -0,0 +1,54 @@
+/* Test for endgrent changing errno for BZ #24696
+   Copyright (C) 2019 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
+   <http://www.gnu.org/licenses/>.  */
+
+#include <stdlib.h>
+#include <sys/types.h>
+#include <grp.h>
+#include <unistd.h>
+#include <errno.h>
+
+#include <support/check.h>
+#include <support/support.h>
+
+/* The following test verifies that if the db NSS Service is initialized
+   with no database (getgrent), that a subsequent closure (endgrent) does
+   not set errno. In the case of the db service it is not an error to close
+   the service and so it should not set errno.  */
+
+static int
+do_test (void)
+{
+  /* Just make sure it's not there, although usually it won't be.  */
+  unlink ("/var/db/group.db");
+
+  /* This, in conjunction with the testroot's nsswitch.conf, causes
+     the nss_db module to be "connected" and initialized - but the
+     testroot has no group.db, so no mapping will be created.  */
+  getgrent ();
+
+  errno = 0;
+
+  /* Before the fix, this would call munmap (NULL) and set errno.  */
+  endgrent ();
+
+  if (errno != 0)
+    FAIL_EXIT1 ("endgrent set errno to %d\n", errno);
+
+  return 0;
+}
+#include <support/test-driver.c>