feat: First version of broker based WireGuard PSK interface

This allows us to run with minimal priviledges in the Rosenpass process itself

util/Cargo.toml

@@ -14,3 +14,4 @@ readme = "readme.md"
 [dependencies]
 base64 = { workspace = true }
 anyhow = { workspace = true }
+rustix = { workspace = true }

util/src/fd.rs

@@ -0,0 +1,12 @@
+use std::os::fd::{OwnedFd, RawFd};
+
+/// Clone some file descriptor
+///
+/// If the file descriptor is invalid, an error will be raised.
+pub fn claim_fd(fd: RawFd) -> anyhow::Result<OwnedFd> {
+    use rustix::{fd::BorrowedFd, io::dup};
+
+    // This is safe since [dup] will simply raise
+    let fd = unsafe { dup(BorrowedFd::borrow_raw(fd))? };
+    Ok(fd)
+}

util/src/lib.rs

@@ -1,4 +1,5 @@
 pub mod b64;
+pub mod fd;
 pub mod file;
 pub mod functional;
 pub mod mem;