commit 99135114ba23c3110b7e4e650fabdc5e639746b7
Author: DJ Delorie <dj@redhat.com>
Date:   Fri Jun 28 18:30:00 2019 -0500

    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.

Note: the test case has not been included in this backport as the
required test harness infrastructure does not exist.
    
diff --git a/nss/nss_db/db-open.c b/nss/nss_db/db-open.c
index 8a83d6b..3fa11e9 100644
--- a/nss/nss_db/db-open.c
+++ b/nss/nss_db/db-open.c
@@ -63,5 +63,9 @@ internal_setent (const char *file, struct nss_db_map *mapping)
 void
 internal_endent (struct nss_db_map *mapping)
 {
-  munmap (mapping->header, mapping->len);
+  if (mapping->header != NULL)
+    {
+      munmap (mapping->header, mapping->len);
+      mapping->header = NULL;
+    }
 }