[Opendnssec-develop] Again: Sharing PIN through POSIX message queues

[Rick van Rein]

Hello Rickard,

I was pretty accurate with my "two years ago" estimate -- here is the PIN daemon
that I proposed in August 2009.  It is based on message queues, the principle
of which is documented in most UNIX manuals, but it is not widely used by
programmers:

http://linux.die.net/man/7/mq_overview
http://www.users.pjwstk.edu.pl/~jms/qnx/help/watcom/clibref/mq_overview.html

Note that the attached code uses the older SysV API, which caught critisism
back then.  The POSIX references above are a little different, but capture
the same idea.  The SysV API is documented here:

http://linux.die.net/man/2/msgget
http://linux.die.net/man/2/msgctl
http://linux.die.net/man/2/msgsnd
http://linux.die.net/man/2/msgrcv

The driving reason for preferring this mechanism for security reasons are:

1. The announcement is not as public as a filesystem reference; that is, it is
   not only protected by user/access settings like a file, but it actually
   is under full control of the PIN serving daemon;

2. The ability to lookup the sender's PID makes it possible to limit service
   to very specific processes, such as those whose PID is stored in a certain
   file in a certain location.

I've been looking through the POSIX mq_ documentation, and cannot find the
process identifier back.  That means that the mileage of this approach may
vary with the platform.  (But now that OpenDNSSEC is ported to Windows, I
suppose that is a basic issue underpinning OpenDNSSEC security anyway!)


Let me know if you need more information!


Cheers,
 -Rick
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