[COMMITTED 2.33] nsswitch: return result when nss database is locked [BZ #27343]

[COMMITTED 2.33] nsswitch: return result when nss database is locked [BZ #27343]

[DJ Delorie]

From: Sergei Trofimovich <slyfox@gentoo.org>
Subject: nsswitch: return result when nss database is locked [BZ #27343]
(cherry picked from commit c3479fb7939898ec22c655c383454d6e8b982a67)

Before the change nss_database_check_reload_and_get() did not populate
the '*result' value when it returned success in a case of chroot
detection. This caused initgroups() to use garage pointer in the
following test (extracted from unbound):

```

int main() {
    // load some NSS modules
    struct passwd * pw = getpwnam("root");

    chdir("/tmp");
    chroot("/tmp");
    chdir("/");
    // access nsswitch.conf in a chroot
    initgroups("root", 0);
}
```

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

diff --git a/nss/nss_database.c b/nss/nss_database.c
index cf0306adc4..e1bef6bd75 100644
--- a/nss/nss_database.c
+++ b/nss/nss_database.c
@@ -398,8 +398,9 @@ nss_database_check_reload_and_get (struct nss_database_state *local,
 	  && (str.st_ino != local->root_ino
 	      ||  str.st_dev != local->root_dev)))
     {
-      /* Change detected; disable reloading.  */
+      /* Change detected; disable reloading and return current state.  */
       atomic_store_release (&local->data.reload_disabled, 1);
+      *result = local->data.services[database_index];
       __libc_lock_unlock (local->lock);
       __nss_module_disable_loading ();
       return true;