Disabling dynamic interface updates is impossible with POSIX capabilities

[israel-lugo]

Hello,

I am using ntpd on a Linux router, with a large routing table and many Netlink messages going on. I want to disable dynamic interface updates, due to a constant error "routing socket reports: No buffer space available". I don't really need it, as new interfaces come up perhaps once a year.

The manpage states that one is supposed to be able to disable dynamic interface list updating, by setting -U 0. Except that is impossible: in ntpd/ntpd.c:ntpdmain(), lines 1063-1075 determine whether dynamic updates are performed:

#  if !defined(HAVE_LINUX_CAPABILITIES) && !defined(HAVE_SOLARIS_PRIVS)
		/*
		 * for now assume that the privilege to bind to privileged ports
		 * is associated with running with uid 0 - should be refined on
		 * ports that allow binding to NTP_PORT with uid != 0
		 */
		disable_dynamic_updates |= (sw_uid != 0);  /* also notifies routing message listener */
#  endif /* !HAVE_LINUX_CAPABILITIES && !HAVE_SOLARIS_PRIVS */

		if (disable_dynamic_updates && interface_interval) {
			interface_interval = 0;
			msyslog(LOG_INFO, "running as non-root disables dynamic interface tracking");
		}

These are the only two references to disable_dynamic_updates anywhere in the file. It is never set to 1 anywhere. The only way this is set to 1 would be if we don't have POSIX capabilities and are running non-root. Setting interface_interval to 0 makes absolutely no difference in this case.

[israel-lugo]

I realize that ntp_timer.c:timer() only calls interface_update() if interface_interval is non-zero, but the fact that I am still getting that message constantly means ntp_io.c:process_routing_msgs() is being called by someone, somewhere, in a timer loop. I have of course verified that the process is running with the proper arguments:

ps u -p 15532 
USER       PID %CPU %MEM    VSZ   RSS TTY      STAT START   TIME COMMAND
ntp      15532  0.5  0.0 110176  5832 ?        Ssl  18:40   0:10 /usr/sbin/ntpd -p /var/run/ntpd.pid -g -U 0 -u 123:123

[hstenn]

Would you please open up an "enhancement" request for this issue at bugs.ntp.org?

[israel-lugo]

Thank you for the feedback, @hstenn. I've opened bug 3428.

I've added some further information there, as I assume bugs.ntp.org is the preferred venue, correct?

[hstenn]

Hi @israel-lugo - yes, bugs.ntp.org is the better place for this. We'll be looking at your issue after 4.2.8p11 comes out.