commit 31d0a4fa646db8b8c97ce24e0ec0a7b73de4fca1
Author: Florian Weimer <fweimer@redhat.com>
Date:   Sat Jun 11 12:12:56 2016 +0200

    nss_db: Fix initialization of iteration position [BZ #20237]
    
    When get*ent is called without a preceding set*ent, we need
    to set the initial iteration position in get*ent.
    
    Reproducer: Add “services: db files” to /etc/nsswitch.conf, then run
    “perl -e getservent”.  It will segfault before this change, and exit
    silently after it.

Index: b/nss/nss_db/db-XXX.c
===================================================================
--- a/nss/nss_db/db-XXX.c
+++ b/nss/nss_db/db-XXX.c
@@ -76,7 +76,7 @@ CONCAT(_nss_db_set,ENTNAME) (int stayope
       keep_db |= stayopen;
 
       /* Reset the sequential index.  */
-      entidx  = (const char *) state.header + state.header->valstroffset;
+      entidx  = NULL;
     }
 
   __libc_lock_unlock (lock);
@@ -249,8 +249,14 @@ CONCAT(_nss_db_get,ENTNAME_r) (struct ST
 	  H_ERRNO_SET (NETDB_INTERNAL);
 	  goto out;
 	}
+      entidx = NULL;
     }
 
+  /* Start from the beginning if freshly initialized or reset
+     requested by set*ent.  */
+  if (entidx == NULL)
+    entidx = (const char *) state.header + state.header->valstroffset;
+
   status = NSS_STATUS_UNAVAIL;
   if (state.header != MAP_FAILED)
     {