Description of problem:

When performing a lookup over netgroups using nss_ldap, this one will always
return success and print the netgroup even though this one doesn't exist... 

The issue happens when using setnetgrent(), getnetgrent(), endnetgrent().
The first call to set the nss lookup key will always return 1 (Success) even if
it didn't find a result... this makes tools like getent netgroup fake_group
always succeed. In fact, getent will do the following:

//
     if (!setnetgrent (key[i]))
       result = 2;               <-- No results found following the manpage, but
with nss_ldap we never fall into this case.
//

Checking the nss_ldap/ldap-nss.c and nss_ldap/ldap-netgrp.c, there are two parts
to fix:

- by the end of the function that answers to setnetgrent() there is a macro that
overrides what ldap_search_s() returns...
- in ldap_search_s() there is no notion from where there was no key set, and
therefore we miss the result report...

I was thinking of something similar to this, it does fix the problem for us.
//
+  /* If we didn't set any key yet (not yet called LOOKUP_SETENT - setXXent()), 
+   * check if we should do it, because if we didn't find any of the results 
+   * then there is no point setting a key. -- jmp
+   */
+  if (sd == NULL &&                                        /* No key yet */
+      (stat == NSS_SUCCESS &&                              /* No transport
issues */
+       ldap_count_entries (__session.ls_conn, *res) == 0)) /* No results found */
+    {
+       debug ("<== _nss_ldap_search_s");
+       return NSS_NOTFOUND;
+    }
+
   /* If no entry was returned, try the next search descriptor. */
   if (sd != NULL && sd->lsd_next != NULL)
     {
//

Version-Release number of selected component (if applicable):
nss_ldap-254-2 (rawhide)
nss_ldap-226-20 (for this BZ)

How reproducible:
Always.

Steps to Reproduce:
1. Setup /etc/nsswitch.conf with netgroup: files ldap
2. Setup an LDAP directory server with an ldif as follows (optional really as
you check non-existant netgroups)
--
dn: cn=real,ou=netgroup,dc=seg,dc=redhat,dc=com
cn: real
ObjectClass: nisNetgroup
ObjectClass: top
nisNetgroupTriple: (,jmp,)
--
3. Succesful case:

   % getent netgroup real
   real (,jmp,)
   % echo $?
   0

4. Failure case:
   
   % getent netgroup unreal
   unreal
   % echo $?
   0
  
Actual results:
Show the non-existant entry and return 0

Expected results:
Don't show anything, fall back into return 2

Additional info:
[PATCH] attached.
Fixes the issue if the query didn't return any contents and we didn't set yet a
key. Notice that in the setnetgrent() call, by the end there is that macro that
sets the key and doesn't remember if we had or not any successful results from
the first ldap_search...  This prevents this from happening by testing
NSS_NOTFOUND previously returned by the fact the LDAP server returned 0 contents
if these were not present.

    Jose