Ralf's Ramblings

Jun 10, 2018 • SysadminPermalink

Fighting Mailman Subscription Spam: Leveling Up

Last week, I blogged about my efforts to fight mailman subscription spam. Enabling SUBSCRIBE_FORM_SECRET as described there indeed helped to drastically reduce the amount of subscription spam from more than 1000 to less than 10 mails sent per day, but some attackers still got through. My guess is that those machines were just so slow that they managed to wait the required five seconds before submitting the form.

So, clearly I had to level up my game. I decided to pull through on my plan to write a simple CAPTCHA for mailman (that doesn’t expose your users to Google). This post describes how to configure and install that CAPTCHA.

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Jun 2, 2018 • SysadminPermalink

Fighting Mailman Subscription Spam: The Easy Way

I recently noticed that both of the Mailman setups that I am running are being abused for subscription spam: Bots would automatically attempt to subscribe foreign email addresses to public mailing lists, resulting in a subscription notification being sent to that address. I am still extremely saddened by the fact that this is a thing—whoever sends this spam has no direct benefit and no way of selling anything (they don’t control the content of the message); the only effect is to annoy the owner of that email address, the victim. That seems to be enough for some. :(

Oh, and my servers’ reputation goes down because people mark these emails as spam. So, more than enough reasons to try and stop this.

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May 28, 2018 • SysadminPermalink

Syncing Contacts Without Exposing Them to the Cloud

I finally have a setup that I am happy with for syncing contacts between my phone and my laptop. Most would probably consider that a solved problem, but I have an extra requirement that rules out most existing solutions:

The data of my contacts must not be exposed in clear text to any machine I do not physically control.

I’m not happy about my own personal data being shared with third parties, and consequently, I will not share the personal data others entrust to me with third parties. This obviously rules out all of these “free” cloud services out there that Apple, Google and others offer—services that are paid with data, and in the case of contact sync frequently paid with the data of others. (This leaves me wonder whether under the GDPR, it is even legal for someone else to consent to my contact data being shared with a cloud provider. I certainly never consented and still my data sits in multiple synced address books. But that’s a discussion for another day.) Moreover, this also rules out putting them e.g. into an ownCloud or Nextcloud hosted on ralfj.de, because that is a VPS that I do not have any physical control over.

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Apr 10, 2018 • Research, RustPermalink

Safe Intrusive Collections with Pinning

In my last post, I talked about the new “pinned references” which guarantee that the data at the memory it points to will not, ever, be moved elsewhere. I explained how they enable giving a safe API to code that could previously only be exposed with unsafe, and how one could go about proving such a thing. This post is about another application of pinned references—another API whose safety relies on the pinning guarantees: Intrusive collections. It turns out that pinned references can almost be used for this, but not quite. However, this can be fixed by extending the guarantees provided by pinned references, as suggested by @cramertj.

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Apr 5, 2018 • Research, RustPermalink

A Formal Look at Pinning

Recently, a new API for “pinned references” has landed as a new unstable feature in the standard library. The purpose of these references is to express that the data at the memory it points to will not, ever, be moved elsewhere. @withoutboats has written about how this solves a problem in the context of async IO. In this post, we take a closer, more formal look at that API: We are going to take a stab at extending the RustBelt model of types with support for pinning.

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Jan 31, 2018 • Research, RustPermalink

Sharing for a Lifetime

This post is about an aspect of the RustBelt paper. Concretely, I’d like to share some of our thoughts on the nature of types and shared references. Let’s see how well this goes. :)

Shared references are an extremely powerful mechanism in the Rust type system, and we’ve had quite some trouble finding a good way of handling them in our formal model. In this post, I will present the model that we came up with.

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Jan 21, 2018 • Research, RustPermalink

RustBelt Conference Talk

Last week, I was in Los Angeles at POPL 2018 to present our paper RustBelt: Securing the Foundations of the Rust Programming Language. The talk has been recorded, so if you want to get a 20-minute summary of the paper, go watch it on YouTube. If you have any questions, feel free to join the forum thread linked below :)

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Dec 26, 2017 • SysadminPermalink

Let's Encrypt Tiny

I think all HTTP communication on the internet should be encrypted – and thanks to Let’s Encrypt, we are now much closer to this goal than we were two years ago. However, when I set up Let’s Encrypt on my server (which is more than a year ago by now), I was not very happy with the official client: The client manages multiple certificates with different sets of domains per certificate, but I found it entirely unclear which commands would replace existing certificates or create a new one. Moreover, I have some special needs: I’ve set up DNSSEC with TLSA records containing hashes of my certificates, so replacing a certificate has to also update DNS and deal with the fact that DNS entries get cached. Lucky enough, Let’s Encrypt is based on open standards, so I was not forced to use their client!

To make a long story short, I decided to write my own Let’s Encrypt client, which I describe in this post.

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Dec 15, 2017 • ResearchPermalink

Interview for People of Programming Languages

POPL 2018, the conference where I will present our RustBelt paper, is doing a series of interviews with senior and junior people from the community: People of Programming Languages. They also asked me if I wanted to be part of this, and of course I accepted. This was the first time I was asked to give an interview, so needless to say, I was super excited! I got the opportunity to talk about how I came to do research in PL, what my research is about, and ramble a bit about why I think Coq is great. If you want to read more, check out my interview. Be sure to also have a look at the other interviews.

Thanks a lot to Jean Yang, the Publicity Chair for POPL 2018, for making this a very pleasant experience. (Though, as you can see, I had to send them a picture, which was certainly the least pleasant part of this. ;)

PS: It seems I have consistent bad luck with my POPL talk slots, because my talk is again in the very last session of the conference. This time, in fact, it’s the very last talk of the main track. Maybe some people read this interview and consider staying anyway :D

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Aug 12, 2017 • Internship, RustPermalink

So Long, and Thanks for All the Fish

Yesterday was the last day of my Rust internship at Mozilla. I can hardly believe that twelve weeks have passed since that post, but my calendar insists. If you want to see what I have done, you can go read the posts that I wrote during the internship. (I almost kept up with the plan of bi-weekly blog posts…) You can also watch the 10-minute video version of this that I made for the internship presentation. The recording is available on Air Mozilla; my talk starts at 2h 14:30.

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Aug 11, 2017 • Internship, RustPermalink

Types as Contracts: Implementation and Evaluation

Some weeks ago, I described Types as Contracts as an approach for how to go about defining Rust’s aliasing-related undefined behavior. One key property of this approach is that it is executable, which means we can actually have a program (in this case, miri) tell us whether some particular Rust test case exhibits undefined behavior or not. I have since then spent most of my time completing and refining this implementation, and running it on miri’s test suite to exercise various bits of the standard library and see whether they are actually following the rules I have been suggesting.

This post is my report on what I found, and how the approach itself changed in response to these findings. It also explains how you can run miri yourself and have it check your code for undefined behavior according to this model. Finally, I discuss some of the things that I would like to look at going forward.

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Jul 17, 2017 • Internship, RustPermalink

Types as Contracts

Over the last couple of weeks of my internship, I have been working on a proposal for the “Unsafe Code Guidelines”. I got some very encouraging feedback at the Mozilla All-Hands, and now I’d like to put this proposal out there and start having a discussion.

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Jul 14, 2017 • Internship, RustPermalink

Undefined Behavior and Unsafe Code Guidelines

Last year, the Rust unsafe code guidelines strike team was founded, and I am on it. :-) So, finally, just one year later, this post is my take at what the purpose of that team is.

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Jul 8, 2017 • Research, RustPermalink

RustBelt: Securing the Foundations of the Rust Programming Language

Just yesterday, we submitted our paper RustBelt: Securing the Foundations of the Rust Programming Language. Quoting from the abstract:

Rust is a new systems programming language that promises to overcome the seemingly fundamental tradeoff between high-level safety guarantees and low-level control over resource management. Unfortunately, none of Rust’s safety claims have been formally proven, and there is good reason to question whether they actually hold. Specifically, Rust employs a strong, ownership-based type system, but then extends the expressive power of this core type system through libraries that internally use unsafe features. In this paper, we give the first formal (and machine-checked) safety proof for a language representing a realistic subset of Rust. Our proof is extensible in the sense that, for each new Rust library that uses unsafe features, we can say what verification condition it must satisfy in order for it to be deemed a safe extension to the language. We have carried out this verification for some of the most important libraries that are used throughout the Rust ecosystem.

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Jun 9, 2017 • RustPermalink

How MutexGuard was Sync When It Should Not Have Been

A couple of weeks ago, our ongoing effort to formalize Rust’s type system lead to us actually discovering a bug in the Rust standard library: MutexGuard implemented Sync in cases where it should not. This could lead to data races in safe programs. Ouch.

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Jun 6, 2017 • Internship, RustPermalink

Exploring MIR Semantics through miri

It’s now been two weeks since my internship started (two weeks already, can you believe it?). In other words, if I want to post “weekly or bi-weekly” updates, I better write one today ;) .

As already mentioned, the goal for this internship is to experiment with unsafe code guidelines by implementing them in miri. Before I tackle that, however, it seemed sensible for me to grab some low-hanging fruit in miri just to make myself familiar with the codebase. It turns out I entered “unsafe code guidelines” territory much quicker than expected. This post is about what I found, and it also serves as a nice demonstration of how we envision my unsafe code guidelines workflow to look like.

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May 23, 2017 • Internship, RustPermalink

Day 1 of My Mozilla Internship, or: How to Specify Program Behavior?

This summer, I am given the awesome opportunity of spending three months in the Mozilla offices in Portland, working on Rust. I am extremely grateful that Mozilla is providing this opportunity to me; hopefully I can give something back by making some hands-on contributions to the Rust ecosystem.

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Jan 20, 2017 • Research, RustPermalink

Talk @ Paris Rust Meetup

This week, I have been at the Paris Rust Meetup. Meeting all sorts of Rust people was great fun, and the Mozilla offices in Paris are absolutely impressive. You should totally check them out if you have a chance.

On that meetup, I gave a short talk about the current status of my formalization of the Rust type system.

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Jan 9, 2016 • Research, RustPermalink

The Scope of Unsafe

I’d like to talk about an important aspect of dealing with unsafe code, that still regularly seems to catch people on the wrong foot:

When checking unsafe code, it is not enough to just check the contents of every unsafe block.

The “scope” in the title refers to the extent of the code that has to be manually checked for correctness, once unsafe is used. What I am saying is that the scope of unsafe is larger than the unsafe block itself.

It turns out that the underlying reason for this observation is also a nice illustration for the concept of semantic types that comes up in my work on formalizing Rust (or rather, its type system). Finally, this discussion will once again lead us to realize that we rely on our type systems to provide much more than just type safety.

Update (Jan 11th): Clarified the role of privacy; argued why evil is the problem.

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Oct 12, 2015 • Research, RustPermalink

Formalizing Rust

My current research project – and the main topic of my PhD thesis – is about developing a semantic model of the Rust programming language and, most importantly, its type system. Rust is an attempt of Mozilla to find a sweet spot in the design space of programming languages: A language that provides low-level resource management (making it a systems language), is convenient for programmers and guards against memory errors and thread unsafety. Other have said and written a lot on why we need such a language, so I won’t lose any more words on this. Let me just use this opportunity for a shameless plug: If you are curious and want to learn Rust, check out Rust-101, a hands-on Rust tutorial I wrote. I am going to assume some basic familiarity with Rust in the following.

Why do we want to do research on Rust? First of all, I’m (becoming) a programming languages researcher, and Rust is an interesting new language to study. It’s going to be fun! Honestly, that’s enough of a reason for me. But there are other reasons: It shouldn’t be a surprise that bugs have been found in Rust. There are lots of things that can be done about such bugs – my take on this is that we should try to prove, in a mathematical rigorous way, that no such bugs exist in Rust. This goes hand-in-hand with other approaches like testing, fuzzing and static analysis. However, we (at my research group) are into formalizing things, so that’s what we are going to do as part of the RustBelt research project.

Update: Added link to RustBelt website.

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Oct 9, 2015 • FunPermalink

Breaking All the Way Out

Do you know the feeling of having done something, and having a website for it somewhere, but not finding the right spot to put a link to that website? I certainly do, and, well… now that I have a blog, I finally do have a place for such links!

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Oct 8, 2015 • MetaPermalink

Welcome

I’ll use this blog to write random articles on things that matter to me, and that I want to share. So far, I don’t know what this will end up being about - probably mostly about programming languages research and related topics, as that’s what I do.

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