fail2ban: never ban the operator's own addresses, and say a failure from one (hq issue 238, ADR 0339)

An agent polling the forge from the operator's home got that home banned for a day and then four weeks, and nothing in the house reached the control-node. Every jail spared only private ranges. The mesh-wide setting own-addresses reaches the machine as a mergeable file whose own content is the empty list, so the module composes while it is unset. A new watch process (root) writes its entries into a list every jail's base ignoreip names as file:, which fail2ban reloads without a restart; it checks every jail names that list and keeps each failure a jail ignored because of it for a day. The new fail2ban_health tool judges the watch, so the controller raises a warning naming node, jail, address and count. The ban verb refuses an address on the setting or on the jail's ignore list before the daemon is asked.
2026-10-13 10:54:49 +02:00
parent 5cd608ba88
commit 93d58f3740
8 changed files with 916 additions and 9 deletions
@@ -17,7 +17,8 @@
    }
  ],
  "tools": [
-    "fail2ban_settings"
+    "fail2ban_settings",
+    "fail2ban_health"
  ],
  "jailing": {
    "into": "/etc/fail2ban/jail.d/mesh.conf",
@@ -29,6 +30,20 @@
      "type": "package",
      "package": "fail2ban"
    },
+    {
+      "id": "state-dir",
+      "type": "directory",
+      "path": "/var/lib/mesh-fail2ban",
+      "mode": "0755"
+    },
+    {
+      "id": "own-addresses-list",
+      "type": "file",
+      "path": "/var/lib/mesh-fail2ban/own-addresses",
+      "mode": "0644",
+      "create-once": true,
+      "content": ""
+    },
    {
      "id": "jail-d",
      "type": "directory",
@@ -58,7 +73,7 @@
      "type": "file",
      "path": "/etc/fail2ban/jail.local",
      "mode": "0644",
-      "content": "[INCLUDES]\n\nbefore = paths-arch.conf\n\n[DEFAULT]\n\n# Never act on the machine itself or on a tunnel peer: the mesh's private range is\n# ${machine:mesh-range}, named here rather than written as a value the module cannot\n# know (novox/hq ADR 0112). Without this, fail2ban could ban the mesh's own nodes.\n# **A ban list never holds a neighbour.** The mesh's own range is named rather than written\n# (novox/hq ADR 0112), and every private range beside it: a source on one is somebody's own\n# network, not the internet. On a machine behind a router that reflects local traffic, every\n# client in the house arrives as the gateway's address — so one mistyped local request banned\n# 192.168.1.1 on the home server and would have cut the whole house off from it (ADR 0186).\nignoreip = 127.0.0.1/8 ::1 ${machine:mesh-range} 10.0.0.0/8 172.16.0.0/12 192.168.0.0/16 169.254.0.0/16 fc00::/7 fe80::/10\n\n# Three failures in a day ban for a day (novox/hq ADR 0179). The attackers this mesh sees pace\n# themselves at one try every ten minutes, under any ten-minute window; a day's window counts\n# them, and a day's ban costs a person who mistyped three times once, from one address, while\n# the mesh's own range is never banned at all.\nbantime  = 1d\nfindtime = 1d\nmaxretry = 3\n\n# Ban through iptables, not through a firewall front-end the machine may not have. ufw is\n# installed on two of this mesh's machines and absent on the other two, and fail2ban finds out\n# only at ban time: the service reports healthy, the jail counts the attempt, the ban command\n# exits 127, and nothing is blocked. Proven on 2026-09-28 -- 'ufw: command not found' on a\n# machine the mesh reported as protected.\n#\n# The action below is this module's own, already used by the recidive jail on every machine\n# here, and it bans in DOCKER-USER as well as INPUT, so a container's published port is\n# covered too.\nbanaction = iptables-allports-dualchain\nbanaction_allports = iptables-allports-dualchain\n\n[sshd]\nenabled = true\nport    = ssh\nlogpath = %(sshd_log)s\nbackend = %(sshd_backend)s\n"
+      "content": "[INCLUDES]\n\nbefore = paths-arch.conf\n\n[DEFAULT]\n\n# Never act on the machine itself or on a tunnel peer: the mesh's private range is\n# ${machine:mesh-range}, named here rather than written as a value the module cannot\n# know (novox/hq ADR 0112). Without this, fail2ban could ban the mesh's own nodes.\n# **A ban list never holds a neighbour.** The mesh's own range is named rather than written\n# (novox/hq ADR 0112), and every private range beside it: a source on one is somebody's own\n# network, not the internet. On a machine behind a router that reflects local traffic, every\n# client in the house arrives as the gateway's address — so one mistyped local request banned\n# 192.168.1.1 on the home server and would have cut the whole house off from it (ADR 0186).\n#\n# **Nor the operator's own addresses** (novox/hq ADR 0339, issue 238): the public addresses the operator names\n# as theirs, in the mesh-wide setting own-addresses. An agent polling the forge from the operator's home banned\n# that home for four weeks on 2026-10-04, and nothing in the house reached the control-node until it was found\n# among 400 bans. The file is written by this module's watch from the setting, one entry per line; fail2ban\n# reads it again within a second of a change, so a new value needs no restart. Empty until the operator\n# fills the setting. A jail that sets its own ignoreip leaves all of this out; the watch says so.\nignoreip = 127.0.0.1/8 ::1 ${machine:mesh-range} 10.0.0.0/8 172.16.0.0/12 192.168.0.0/16 169.254.0.0/16 fc00::/7 fe80::/10 file:/var/lib/mesh-fail2ban/own-addresses\n\n# Three failures in a day ban for a day (novox/hq ADR 0179). The attackers this mesh sees pace\n# themselves at one try every ten minutes, under any ten-minute window; a day's window counts\n# them, and a day's ban costs a person who mistyped three times once, from one address, while\n# the mesh's own range is never banned at all.\nbantime  = 1d\nfindtime = 1d\nmaxretry = 3\n\n# Ban through iptables, not through a firewall front-end the machine may not have. ufw is\n# installed on two of this mesh's machines and absent on the other two, and fail2ban finds out\n# only at ban time: the service reports healthy, the jail counts the attempt, the ban command\n# exits 127, and nothing is blocked. Proven on 2026-09-28 -- 'ufw: command not found' on a\n# machine the mesh reported as protected.\n#\n# The action below is this module's own, already used by the recidive jail on every machine\n# here, and it bans in DOCKER-USER as well as INPUT, so a container's published port is\n# covered too.\nbanaction = iptables-allports-dualchain\nbanaction_allports = iptables-allports-dualchain\n\n[sshd]\nenabled = true\nport    = ssh\nlogpath = %(sshd_log)s\nbackend = %(sshd_backend)s\n"
    },
    {
      "id": "jail-sshd",
@@ -67,6 +82,36 @@
      "mode": "0644",
      "content": "[sshd]\nenabled = true\nport    = ssh\nlogpath = %(sshd_log)s\nbackend = %(sshd_backend)s\nmaxretry = 3\nfindtime = 1d\nbantime  = 1d\n"
    },
+    {
+      "id": "own-addresses",
+      "type": "file",
+      "path": "/etc/fail2ban/mesh-own-addresses.json",
+      "mode": "0644",
+      "merge": "json",
+      "takes-settings": [
+        "own-addresses"
+      ],
+      "trusted": true,
+      "content": "{\n  \"own-addresses\": []\n}\n"
+    },
+    {
+      "id": "watch",
+      "type": "process",
+      "name": "fail2ban-watch",
+      "artifact": "tools",
+      "run": [
+        "./fail2ban-tools",
+        "watch"
+      ],
+      "health": {
+        "kind": "tool",
+        "tool": "fail2ban_health",
+        "interval": "60s",
+        "timeout": "10s",
+        "looks": 2,
+        "grace": "90s"
+      }
+    },
    {
      "id": "log",
      "type": "file",
@@ -108,7 +153,10 @@
        "jail-recidive",
        "action-dualchain",
        "composed-jails"
-      ]
+      ],
+      "health": {
+        "kind": "unit"
+      }
    }
  ],
  "build": {