Deploying `felis nano` to a real Rocky Linux 10 host surfaced four defects that
no local check could see. Fixed together because they all sit on the same path
from `curl|bash` to a running felis-nano.service.
* docker killed the nano install on EL10. `acquire_nano_binary` pulled in
docker purely to build the binary; on Rocky 10.2 the docker-ce el10 rpms
install but dockerd refuses to start, so the install died at
`systemctl enable --now docker`. nano needs one static binary, not an image,
so the docker dependency is gone: fetch_source -> install_go_toolchain
(pinned FELIS_GO_VERSION, default 1.26.4, amd64/arm64) -> build_nano_binary.
* the built binary could not be exec'd by systemd (203/EXEC). The Go linker
renames its output out of $TMPDIR, and a same-filesystem rename carries the
source SELinux label, so `go build -o /usr/local/bin/felis` produced a binary
labelled user_tmp_t rather than bin_t. root is unconfined and could run it by
hand, which is what made this look fine, but the DynamicUser service could
not. build_nano_binary now stages the output and installs it as a fresh file
so the policy type transition labels it bin_t, with restorecon as a belt.
* re-running the installer did not converge. `systemctl enable --now` is a
no-op on an already-active unit, so a rebuilt binary was installed while the
old process kept running. Now enable + restart.
* the Velocity wiring comment in cmd/felis/nano.go was wrong. authlib appends
/session/minecraft/hasJoined itself, so -Dmojang.sessionserver takes the base
URL only, as the installer has always printed.
Also bind to loopback by default. hasJoined is unauthenticated by protocol --
authlib speaks the vanilla sessionserver dialect and sends no token -- so a
public bind is an open auth relay: anyone can point their own proxy at it and
spend this host's egress IP on Mojang until Mojang rate-limits it and the
operator's own players stop getting in. It is not an identity bypass (a caller
still needs a serverId hash bound to their own server key, which the upstream
Yggdrasil validates), but it is someone else's traffic on your address.
FELIS_NANO_LISTEN and the -listen flag now default to 127.0.0.1:8081, which a
same-host Velocity reaches unchanged; serving an off-host proxy is an explicit
opt-in. configure_nano_firewall no longer opens a port for a loopback bind, and
summary_nano prints the real bind address plus the relay warning.
Verified on the target host: installs with no docker present, service active,
binary labelled bin_t, `ss` shows LISTEN 127.0.0.1:8081, an external request is
unreachable, and an in-host request returns 204 with the login logged.
BREAKING CHANGE: felis nano defaults to 127.0.0.1:8081 instead of 0.0.0.0:8081.
A Velocity proxy on another machine must now set FELIS_NANO_LISTEN (or -listen)
to a reachable address, and should allow that port only from the proxy's IP.
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