login: chdir to home (file scheme) before restricting the namespace

The login shell spawn was failing/hanging because login inherits its CWD
from init, which on the live image is on the 'initfs' scheme.
apply_login_schemes() switches to a namespace with only DEFAULT_SCHEMES
(no 'initfs'), leaving that inherited CWD fd unresolvable; relibc resolves
paths through the CWD fd (AT_REDOX_CWD_FD), so the shell child's chdir +
execve then fail with ENOENT (getty respawns login in a loop) or hang.
chdir into the user's home (on the always-present 'file' scheme, fallback
'/') while still in the full namespace, so the CWD fd stays valid after
the restriction and the shell spawns.

src/bin/login.rs

@@ -154,6 +154,22 @@ pub fn main() {
                     continue;
                 }
                 Some(user) => {
+                    // Establish a working directory on the `file` scheme (the
+                    // user's home) BEFORE any namespace restriction. login runs
+                    // with the CWD inherited from init, which on the live image
+                    // lives on the `initfs` scheme. apply_login_schemes() below
+                    // switches to a namespace containing only DEFAULT_SCHEMES
+                    // (which excludes `initfs`), after which that inherited CWD
+                    // fd is unresolvable — and because relibc resolves paths via
+                    // the CWD fd (AT_REDOX_CWD_FD), the login shell's spawn
+                    // (Command child chdir + execve) then fails or hangs. Doing
+                    // this chdir here, while still in the full namespace, points
+                    // the CWD at `file:` (home, fallback `/`), which remains
+                    // valid inside the restricted login namespace.
+                    if std::env::set_current_dir(&user.home).is_err() {
+                        let _ = std::env::set_current_dir("/");
+                    }
+
                     if user.is_passwd_blank() {
                         if let Ok(mut motd) = File::open(MOTD_FILE) {
                             io::copy(&mut motd, &mut stdout).r#try(&mut stderr);