One of the medium-term possibilities we’re seriously considering for NTPsec is moving the entire codebase out of C into a language with no buffer overruns, and in general much stronger security and correctness guarantees.
This would have been a crazy pipe dream starting from the codebase we inherited in 2015, which was 231KLOC of grubby, portability-shim-laden C. But NTPsec is a lot smaller and cleaner now at 62KLOC of C (that’s just 27% of the original size). It’s been brought up to pretty tight C99/ANSI standards conformance, and the few remaining platform dependencies are either already well isolated or can easily be made so. That makes moving the whole shebang at least thinkable.
When we had our first tentative internal discussions about this, we thought of it as a far-future possibility - two or three years out at minimum. But the technological surround is changing fast, rapidly enough that we’ve actually started preparing the ground with some changes to the codebase intended to make a future translation easier. This is an easy call because they’re virtuous code cleanups even if we never move.
One such cleanup: we’ve made a strong start on banishing unions and type punning from the code. These are not going to translate into any language with the correctness properties we want.
Another necessary step will be to corral the few remaining platform dependencies into well-isolated library modules, so the vast bulk of the code will in principle translate mechanically into whatever binding of the ANSI/POSIX API the new language supports.
There aren’t many such dependencies left. In fact, by translation time we expect to have just the following:
We need adjtime()/adjtimex, obviously - the clock setting and skewing calls designed for NTP and present on all modern UNIX-like OSes.
We need to be able to extract UDP arrival timestamps from the control data returned by recvmsg(2). All Unix-likes have ways to do this but the ways aren’t standardized.
Under Linux, some SECCOMP initialization and capability dances having to do with dropping root and closing off privilege-escalation attacks as soon as possible after startup.
I specified "at translation time" because right now we have a fourth dependency; we rely on getifaddrs(3) or some local equivalent to iterate over all of the host’s network interfaces. We expect to get rid of that one, however, by relying on the standardized API for the IPv4/IPv6 wildcard address that probably didn’t exist when the NTP Classic code was written.
Now for the exciting questions: which language, and when?
We don’t have answers to those yet, but the field is narrowing and the time we might attempt a translation is getting closer - in the most optimistic case it could be as little as 6 to 9 months out. The catalyzing event is not just the emergence of two plausible candidate languages but the fact that both seem now to have reached a self-sustaining community size, so we can be reasonably confident they won’t croak and leave us stranded.
No prize for guessing that our two plausible candidates are Go and Rust.
There’s lots of web evangelism around both languages, so I’m not going to attempt a detailed comparison here. I’m just going to hit a few high points about how their traits intersect with NTPsec’s particular needs.
Probably the first question that will occur to a lot of you is: "Huh? Wouldn’t the stop-the-world pauses from garbage collection rule out Go? And the answer is…they might, but (a) the actual time-critical sections in NTP are small and wrapped tightly around the clock-manipulation calls, and (b) Go’s runtime allows you to lock out GC during critical sections.
In any case, the Go developers have a pretty convincing story about holding stop-the-world pauses down to the small-number-of-milliseconds range. We’ll have to measure, but that just might be tolerable even without the GC lockout.
Still, the absence of GC overhead is a point in Rust’s favor. So is Corrode, the automatic C-to-Rust translator. The Go developers wrote a translator to move their Go compiler from C to Go, but it has no documentation and "Here Be Dragons!" warnings in the README.
Russ Cox’s talk on the C-to-Go translator claims it handles a large subset of C that notably does not include…unions and certain kinds of goto. These are restrictions we can deal with. It may be usable. And if it’s not, maybe I can up-gun it until it is - language parsing and translation is a kind of problem I’m pretty good at and enjoy working.
In the end it might come down to which language I feel more
comfortable in. (It’s good to be
king the principal coder
at times like this.) And I don’t know which that’ll be yet.
I’ve taught myself Go (there’ll be a blog post here about that) but not yet Rust. I do have a nice medium-sized first Rust project planned, about which more when I actually do it.
I want to finish by saying that I find it rather exciting to be working at a time when replacing C in core infrastructure like NTP is even thinkable. I’ve been writing steadily in C since 1983, and am correspondingly deeply aware of its quirks and flaws. Despite my huge investment of time in the language, I’m ready.
I’m ready because buffer overruns and wild-pointer errors just suck. The pressure on systems programmers now to up our game and lower our defect rates is entirely a good thing. To the extent that NTP can set an example there, I am willing to help lead the way to a less crashy future.