osconfig: install root ssh keys to /var/roothome

The current location via tmpfiles.d to install the root ssh keys
seems to be not working. There is an error that `/root/.ssh` does
not exist from `systemd-tmpfiles-setup` and indeed the authorized_keys
file is on in `/root/.ssh`.

It seems like everything else in the firstboot in
tmpfiles.d is refering to `/var/roothome` instead of `/root` and
switching to this for the location of the ssh keys solves the
issue.

Co-authored-by: Colin Walters <walters@verbum.org>

lib/src/install/osconfig.rs

@@ -1,8 +1,10 @@
+use std::borrow::Cow;
 use std::io::Write;
 
-use anyhow::Result;
+use anyhow::{Context, Result};
+use camino::{Utf8Path, Utf8PathBuf};
 use cap_std::fs::Dir;
-use cap_std_ext::cap_std;
+use cap_std_ext::{cap_std, dirext::CapStdExtDirExt};
 use fn_error_context::context;
 use ostree_ext::ostree;
 
@@ -17,8 +19,22 @@ pub(crate) fn inject_root_ssh_authorized_keys(
 ) -> Result<()> {
     // While not documented right now, this one looks like it does not newline wrap
     let b64_encoded = ostree_ext::glib::base64_encode(contents.as_bytes());
+
+    // Eagerly resolve the path of /root in order to avoid tmpfiles.d clashes/problems.
+    // If it's local state (i.e. /root -> /var/roothome) then we resolve that symlink now.
+    let roothome_meta = root.symlink_metadata_optional("root")?;
+    let root_path = if roothome_meta.as_ref().filter(|m| m.is_symlink()).is_some() {
+        let path = root.read_link("root")?;
+        Utf8PathBuf::try_from(path)
+            .context("Reading /root symlink")
+            .map(Cow::Owned)?
+    } else {
+        Cow::Borrowed(Utf8Path::new("root"))
+    };
+
     // See the example in https://systemd.io/CREDENTIALS/
-    let tmpfiles_content = format!("f~ /root/.ssh/authorized_keys 600 root root - {b64_encoded}\n");
+    let tmpfiles_content =
+        format!("f~ /{root_path}/.ssh/authorized_keys 600 root root - {b64_encoded}\n");
 
     crate::lsm::ensure_dir_labeled(root, ETC_TMPFILES, None, 0o755.into(), sepolicy)?;
     let tmpfiles_dir = root.open_dir(ETC_TMPFILES)?;
@@ -40,6 +56,35 @@ fn test_inject_root_ssh() -> Result<()> {
 
     // The code expects this to exist, reasonably so
     root.create_dir("etc")?;
+    // Test with a symlink
+    root.symlink("var/roothome", "root")?;
+    inject_root_ssh_authorized_keys(root, None, "ssh-ed25519 ABCDE example@demo\n").unwrap();
+
+    let content = root.read_to_string(format!("etc/tmpfiles.d/{ROOT_SSH_TMPFILE}"))?;
+    assert_eq!(
+        content,
+        "f~ /var/roothome/.ssh/authorized_keys 600 root root - c3NoLWVkMjU1MTkgQUJDREUgZXhhbXBsZUBkZW1vCg==\n"
+    );
+
+    root.create_dir("etc")?;
+    root.remove_file("root")?;
+    root.create_dir("root")?;
+    inject_root_ssh_authorized_keys(root, None, "ssh-ed25519 ABCDE example@demo\n").unwrap();
+
+    let content = root.read_to_string(format!("etc/tmpfiles.d/{ROOT_SSH_TMPFILE}"))?;
+    assert_eq!(
+        content,
+        "f~ /var/roothome/.ssh/authorized_keys 600 root root - c3NoLWVkMjU1MTkgQUJDREUgZXhhbXBsZUBkZW1vCg==\n"
+    );
+    Ok(())
+}
+
+#[test]
+fn test_inject_root_ssh_dir() -> Result<()> {
+    let root = &cap_std_ext::cap_tempfile::TempDir::new(cap_std::ambient_authority())?;
+
+    root.create_dir("etc")?;
+    root.create_dir("root")?;
     inject_root_ssh_authorized_keys(root, None, "ssh-ed25519 ABCDE example@demo\n").unwrap();
 
     let content = root.read_to_string(format!("etc/tmpfiles.d/{ROOT_SSH_TMPFILE}"))?;