OpenBSD has the wonderful pledge() and unveil() syscalls:

https://www.youtube.com/watch?v=bXO6nelFt-E

Not only are they super useful (the program itself can drop privileges – like, it can initialize itself, read some files, whatever, and then tell the kernel that it will never do anything like that again; if it does, e.g. by being exploited through a bug, it gets killed by the kernel), but they are also extremely easy to use.

Imagine a server program with a connected socket in file descriptor 0. Before reading any data from the client, the program can do this:

unveil("/var/www/whatever", "r");
unveil(NULL, NULL);
pledge("stdio rpath", NULL);

Done. It’s now limited to reading files from that directory, communicating with the existing socket, stuff like that. But it cannot ever read any other files or exec() into something else.

I can’t wait for the day when we have something like this on Linux. There have been some attempts, but it’s not that easy. And it’s certainly not mainstream, yet.

I need to have a closer look at Linux’s Landlock soon (“soon”), but this is considerably more complicated than pledge()/unveil():

https://landlock.io/

(#v7d7d4a) @movq@www.uninformativ.de I like this idea 👌 Very neat!

(#v7d7d4a) @movq@www.uninformativ.de That sounds great! (Well, they actually must have recorded the audio with a potato or so.) You talked about pledge(…) and unveil(…) before, right? I somewhere ran across them once before. Never tried them out, but these syscalls seem to be really useful. They also have the potential to make one really rethink about software architecture. I should probably give this a try and see how I can improve my own programs.