pledge and unveil on OpenBSD

[amrfti]

This patch implements native OpenBSD hardening for the i2pd daemon with unveil(2) and pledge(2) by placing a privledge restriction block at the end of Daemon::init. We get paths for tunconf, tunnelsdir, datadir, and certsdir from the config map.

Paths for name resolution (/etc/resolv.conf and /etc/hosts) are automatically unveiled by the dns promise.

[amrfti]

Upon further testing I believe this still has some issues. In my first commit, I was lacking some additional paths that may have conditionally needed to be unveiled based on given arguments. Yet even still there are some strange issues that I believe are a result of some arguments not being initialized to their default fallback options until after we've finished unveiling. For example, I created this error while testing:

# i2pd --logfile /root/.i2pd/i2pd.log
i2pd: Could not create pid file /root/.i2pd/i2pd.pid: No such file or directory

I believe at the time I unveil the pidfile path, it's unintialized, which causes it to never get unveiled. I need to do more testing, feedback welcome.

[orignal]

daemon/Daemon.cpp:317:76: error: function definition is not allowed here
317 | static void UnveilConfigOption(const std::string& key, const char* mask) {
| ^
daemon/Daemon.cpp:337:4: error: use of undeclared identifier 'UnveilConfigOption'
337 | UnveilConfigOption(rule.first, rule.second);
| ^

Please refrain from using nested functions.

[sonya-blade]

suppose it'd be best to go the "official" way:

• submit the patch to the ports@openbsd.org, where it'd be reviewed and tested;
• after the acceptance of the patch by community - merge in upstream from OpenBSD cvsweb or git
  thank you

[daviduhden]

Thanks for working on OpenBSD hardening. I agree with the issue reported by orignal, and here is the precise correction.

C++ does not allow defining a named function inside another function. In this patch, static void UnveilConfigOption(...) is defined inside Daemon::init, which causes the compile error: function definition is not allowed here.

Please move that helper out of Daemon::init, for example to anonymous namespace file scope, or replace it with a local lambda and keep the rest of the logic unchanged.

Also please fix the PR text typo: privledge -> privilege.