[ntp:hackers] Protocol specification modification for MS-SNTP
abartlet at samba.org
Mon Jul 13 01:19:26 UTC 2009
On Sun, 2009-07-12 at 19:42 +0000, Dave Hart wrote:
> On Sun, Jul 12, 2009 at 7:31 PM, Danny Mayer wrote:
> > Andrew Bartlett wrote:
> >> mssntp allows certain networks to use the NTP server as the time source
> >> in an Active Directory-like domain. (A member of an AD domain will
> >> contact it's domain controller to obtain authenticated time). Used in
> >> conjunction with Samba4 as an AD domain controller, when domain members
> >> attempt to obtain authenticated time from the NTP server, the Samba4
> >> instance on the same host is contacted to provide a signature for the
> >> reply.
> > So why not try and contact the domain controller instead of involving Samba?
> Samba4 is the domain controller in this case. Someone could
> theoretically write similar code to run on Windows domain controllers,
> but it hasn't happened yet. Keep in mind that Windows domain members
> looking for domain-signed time are asking only their own domain
> controllers for such signed NTP replies. When that domain controller
> is Samba4 operating as a DC, ntpd integrates with Samba to accomplish
> the [MS-SNTP] style of signed NTP replies to unsigned requests, using
> a secret shared between the DC(s) and the member machine.
Indeed. This code path only happens on a machine that is already
running Samba4 as an Active Directory Domain Controller, and only (as I
understand it) only when a network is specifically blessed by the
administrator (the mssntp restrict bit) as containing such clients.
> >> See ntpd_signd_socket to set the location of the unix domain socket over
> >> which NTPd and Samba4 communicate.
> > The code should not be using Unix domain sockets. It needs to use either
> > AF_INET or AF_INET6.
> The communication is with other software running on the same host, why
> tie up UDP or TCP ports and involve the stack in purely local
> interprocess communication?
It is actually more important than that, and the decision was more
deliberate. The use of a unix domain socket allows the use of file
system access control to strictly ensure that only NTPd can sign
authenticated time requests.
Samba creates the ntp_signd_socket directory with strict permissions to
ensure this feature isn't abused by other users on the system.
Authentication Developer, Samba Team http://samba.org
Samba Developer, Cisco Inc.
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