Use reserved port only when required for NIS look-ups

[Honza Horak]

On 08/10/2012 07:41 PM, Jeff Law wrote:
> On 08/10/2012 07:22 AM, Honza Horak wrote:
>> when root asks NIS server for any information, reserved port is used
>> every-time. Having a client with many look-ups with root privileges we
>> can get to a state where all reserved ports are exhausted and some other
>> services that need to bind to a reserved port can eventually fail.
> Certainly using privileged ports when they're not strictly necessary is
> a problem.  Both in terms of being unable to get one when it's needed
> and in terms of grabbing a reserved port that prevents another service
> from running.
>
> Not being familiar with the development history behind YP, is there a
> particular reason why privileged ports were always used for lookups from
> processes with root privs?

I think it was designed as a cheap way to authorize requests.

>> One ancient discussion about limited reserved ports count with regards
>> to well-known ports is available at [1], but this is something different.
> Agreed.  FWIW, there's been some talk of a whitelist/blacklist to deal
> with that particular problem.
>
>> NIS server is able to be "secured" with a configuration, where
>> administrator marks some maps as "secure" (basically maps with
>> passwords) and only connections form a reserved port are served in that
>> case. So if we used non-reserved ports for all look-ups, some of them
>> wouldn't be served.
> Understood.  Presumably there's no way for the client to get that
> information from the server?

Afaik there is no such way currently and I don't think another remote 
request would be a good idea with regards to performance.

>> "Reserved ports are the ports from 0 to 1024. Only root users can bind
>> to these ports. In previous releases, NIS commands attempted to bind to
>> reserved ports by default. If there are numerous client requests, all
>> the reserved ports can be consumed. This version of NIS enables binding
>> to reserved ports for select commands or daemons when accessing secure
>> maps which results in reduced usage of reserved ports by NIS. This
>> change does not compromise performance or security."
> Just to be clear, this is what HP did for HPUX11, right?  They're really
> looking for glibc to do something similar for Linux.

Yes, exactly.

> How did they handle the client side configuration for hpux11?  Did we
> ever get information from HP about that?

I haven't found any info by myself, but asked Paul in 
https://bugzilla.redhat.com/show_bug.cgi?id=689424.

> As far as the patch itself:
> +
> +      if ((res = __get_clnt_socket(&clnt_sock, &clnt_sin, inmap)) !=
> YPERR_SUCCESS)
> +        return res;
>
> Do you have the test inverted here?  Don't you want to return "res" for
> YPERR_SUCCESS?

No, we want to continue for YPERR_SUCCESS and interrupt function for 
anything else.

Regards,
Honza