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/