Hacker News Reader

What's required for something to be a shell? IMO a minimal shell would have some command line editing and parser, the ability to launch applications, job control, scripting ability, and I/O redirection. These can all be done in the context of a Capsicum-sandboxed shell, where the applications that can be run, and files that can be read/written by the shell, are only those explicitly made available to the shell.

View on HN

If the result of your sandboxed shell is that it can run any program in PATH, which is sort of the basic function of a shell, then what is the value of the sandbox? I'd say one core feature is the ability to use su or sudo to escalate privileges and install a new application, and then run that application. If you have some whitelist of PATH applications at _start, that's impossible. Meanwhile, you can run dd or cc or rm or chmod and do whatever you like. So I'm just not seeing the value of sandboxing a shell.

I think there's a lot of value in sandboxing more constrained applications, especially with untrusted inputs, like web browsers, individual commands, etc. But I don't buy that you can meaningfully reduce the privileges of a shell without losing the quintessential features of a shell.

Reply on news.ycombinator.com