deploy: add firewalld direct-rule flood-mitigation script (per-IP hashlimit on the IRC ports); gitignore the pinned bin/ artifact

.gitignore

@@ -15,3 +15,4 @@ Cargo.lock
 *.xlines
 *.metadata
 *.reputation
+bin/

deploy/firewalld-echoircd.sh

@@ -0,0 +1,64 @@
+#!/usr/bin/env bash
+# echoIRCd kernel-layer flood mitigation — defense-in-depth on top of the ircd's own
+# per-IP `accept_rate` limiter. Drops excess NEW connections to the IRC client ports
+# (per source IP) in the kernel, before they ever reach the daemon.
+#
+# THIS BOX RUNS firewalld, so the rule is installed through firewalld's DIRECT interface
+# (`firewall-cmd --direct`). firewalld then owns the rule — it won't be flushed on a
+# `firewall-cmd --reload`, and `--permanent` persists it across reboot. (A raw
+# `iptables -I INPUT ...` would be silently wiped the next time firewalld rebuilds its
+# ruleset, which is why that approach is wrong here.)
+#
+# SAFE: it only DROPs the rate-limited *excess* to 6767/6770. It changes no zone,
+# service, or default policy; ports 6767/6770 stay open as firewalld already has them.
+# Loopback is exempt (the liveness probe + local tools). Idempotent and one-command
+# removable.
+#
+#   Apply:   sudo deploy/firewalld-echoircd.sh add
+#   Remove:  sudo deploy/firewalld-echoircd.sh del
+#   Show:    sudo deploy/firewalld-echoircd.sh show
+#
+# Uses iptables `hashlimit` (per-source-IP). firewalld rich rules can't express this —
+# their `limit` is a single global token bucket, not per-source — so a direct rule is
+# the right tool. IPv4 only (the ircd binds 0.0.0.0); add an ipv6 rule if you ever bind ::.
+set -u
+
+PORTS="6767,6770"       # IRC client ports (plaintext + TLS); S2S 7700 intentionally left alone
+RATE="30/second"        # sustained NEW connections/sec per source IP
+BURST="60"              # instantaneous burst allowed per source IP
+ACTION="${1:-}"
+
+# the raw rule (added into INPUT at priority 0 = top): drop NEW conns to the IRC ports
+# from any single source IP that exceeds the rate. `! -i lo` exempts loopback.
+RULE=(ipv4 filter INPUT 0
+    ! -i lo -p tcp -m multiport --dports "$PORTS"
+    -m conntrack --ctstate NEW
+    -m hashlimit --hashlimit-name ircrate --hashlimit-mode srcip
+    --hashlimit-above "$RATE" --hashlimit-burst "$BURST"
+    -j DROP)
+
+add_one() { firewall-cmd "$@" --direct --add-rule "${RULE[@]}"; }
+del_one() { firewall-cmd "$@" --direct --remove-rule "${RULE[@]}" >/dev/null 2>&1 || true; }
+
+case "$ACTION" in
+    add)
+        del_one            # runtime: clear any prior copy (idempotent)
+        del_one --permanent
+        add_one            # runtime (takes effect now)
+        add_one --permanent  # persists across reboot / reload
+        echo "echoircd rate-limit added via firewalld direct rule: ports ${PORTS}, ${RATE} burst ${BURST} per source IP (runtime + permanent)"
+        ;;
+    del)
+        del_one
+        del_one --permanent
+        echo "echoircd rate-limit removed (runtime + permanent)"
+        ;;
+    show)
+        echo "== runtime direct rules =="; firewall-cmd --direct --get-all-rules
+        echo "== permanent direct rules =="; firewall-cmd --permanent --direct --get-all-rules
+        ;;
+    *)
+        echo "usage: $0 {add|del|show}" >&2
+        exit 1
+        ;;
+esac