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fail2drop.go
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fail2drop.go
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package main
import (
_ "embed"
"errors"
"fmt"
"log"
"net"
"os"
"os/exec"
"regexp"
"strings"
"sync"
"syscall"
nf "github.com/google/nftables"
"github.com/google/nftables/expr"
"github.com/nxadm/tail"
"gopkg.in/yaml.v3"
)
const (
version = "0.14.8"
name = "fail2drop"
prefix = "/usr/local/bin/"
)
type logsearch struct {
set string
logfile string
tag string
ipregex string
bancount int
}
var (
//go:embed unit.tmpl
unittmpl string
//go:embed fail2drop.yml
cfgtmpl string
whitelist []string
config = "/etc/" + name + ".yml"
varlog = "/var/log/" + name + ".log"
unitname = "/etc/systemd/system/" + name + ".service"
noaction = false
once = false
wg sync.WaitGroup
)
func usage(msg string) {
help := name + " v" + version + " - Drop repeat-offending IP addresses in-kernel (netfilter)\n" +
"Repo: github.com/pepa65/fail2drop\n" +
"Usage: " + name + " [ OPTION | CONFIGFILE ]\n" +
" OPTION:\n" +
" -o|once: Add to-be-banned IPs in a single run (or from 'cron').\n" +
" -n|noaction: Do a 'once' single run without affecting the system.\n" +
" -i|install: Install the binary, a template for the configfile, the\n" +
" systemd unit file and enable & start the service.\n" +
" -u|uninstall: Stop & disable the service and remove the unit file.\n" +
" -h|help: Show this help text.\n" +
" -V|version: Show the version.\n" +
" CONFIGFILE: Used if given, otherwise '" + name + ".yml' in the current\n" +
" directory or finally '/etc/" + name + ".yml' will get used.\n" +
" Privileges are required to run, except for 'noaction', 'help' and 'version'."
fmt.Println(help)
if msg != "" {
fmt.Println("\n", msg)
os.Exit(1)
}
os.Exit(0)
}
func banip(ipaddr, set string) {
if !noaction {
var err error
conn := &nf.Conn{}
fail2drop := &nf.Table{}
tables, _ := conn.ListTablesOfFamily(nf.TableFamilyINet)
for _, t := range tables {
if t.Name == "fail2drop" {
fail2drop = t
break
}
}
if fail2drop.Name != "fail2drop" {
log.Fatalln("Error: nftable table inet fail2drop not found")
}
chain := &nf.Chain{}
chains, _ := conn.ListChainsOfTableFamily(nf.TableFamilyINet)
for _, c := range chains {
if c.Name == "FAIL2DROP" {
chain = c
break
}
}
if chain.Name != "FAIL2DROP" {
log.Fatalln("Error: nftable chain FAIL2DROP on table inet fail2drop not found")
}
rule := &nf.Rule{}
rules, _ := conn.GetRules(fail2drop, chain)
for _, r := range rules { // Use UserData (IP) as ID for a rule
if string(r.UserData) == ipaddr {
return
}
}
if strings.Contains(ipaddr, ":") { // IPv6
// nft add rule inet fail2drop FAIL2DROP ip6 saddr IPADDR counter drop
rule = &nf.Rule{
UserData: []byte(ipaddr),
Table: fail2drop,
Chain: chain,
Exprs: []expr.Any{
// payload ip6 => reg 1
&expr.Payload{
DestRegister: 1,
Base: expr.PayloadBaseNetworkHeader,
Offset: 8,
Len: 16,
},
// compare reg 1 eq to IPADDR
&expr.Cmp{
Op: expr.CmpOpEq,
Register: 1,
Data: []byte(net.ParseIP(ipaddr)),
},
&expr.Counter{Bytes: 0, Packets: 0},
// immediate reg 0 drop
&expr.Verdict{
Kind: expr.VerdictDrop,
},
},
}
} else { // IPv4
// nft add rule inet fail2drop FAIL2DROP ip saddr IPADDR counter drop
rule = &nf.Rule{
UserData: []byte(ipaddr),
Table: fail2drop,
Chain: chain,
Exprs: []expr.Any{
// payload ip => reg 1
&expr.Payload{
DestRegister: 1,
Base: expr.PayloadBaseNetworkHeader,
Offset: 12,
Len: 4,
},
// compare reg 1 eq to IPADDR
&expr.Cmp{
Op: expr.CmpOpEq,
Register: 1,
Data: []byte(net.ParseIP(ipaddr).To4()),
},
&expr.Counter{Bytes: 0, Packets: 0},
// immediate reg 0 drop
&expr.Verdict{
Kind: expr.VerdictDrop,
},
},
}
}
conn.AddRule(rule)
err = conn.Flush()
if err != nil {
log.Fatalln(err)
}
}
log.Printf("[%s v%s] '%s' ban %s\n", name, version, set, ipaddr)
}
func process(logsearch logsearch, line string, ipcount map[string]int) {
if !strings.Contains(line, logsearch.tag) {
return
}
regex := regexp.MustCompile(logsearch.ipregex)
results := regex.FindStringSubmatch(line)
if len(results) == 0 {
return
}
// Search for IPv4
regex = regexp.MustCompile(`[1-9][0-9]*\.[1-9][0-9]*\.[1-9][0-9]*\.[1-9][0-9]*`)
ipaddrs := regex.FindStringSubmatch(results[0])
if len(ipaddrs) == 0 { // Search for IPv6
regex = regexp.MustCompile(`[0-9a-fA-F]{1,4}(:[0-9a-fA-F]{1,4}){7}`)
if len(ipaddrs) == 0 {
return
}
}
ipaddr := ipaddrs[0]
for _, ip := range whitelist {
if ip == ipaddr {
return
}
}
n := ipcount[ipaddr]
if n == -1 { // Banned already
return
}
n += 1
if n > logsearch.bancount {
ipcount[ipaddr] = -1
banip(ipaddr, logsearch.set)
} else {
ipcount[ipaddr] = n
}
}
func follow(logsearch logsearch) {
defer wg.Done()
ipcount := map[string]int{}
var t *tail.Tail
var err error
if once {
t, err = tail.TailFile(logsearch.logfile, tail.Config{MustExist: true, CompleteLines: true})
} else {
t, err = tail.TailFile(logsearch.logfile, tail.Config{MustExist: true, CompleteLines: true, Follow: true, ReOpen: true})
}
if err == nil {
for line := range t.Lines {
process(logsearch, line.Text, ipcount)
}
}
}
func initnf() {
if noaction {
return
}
conn := &nf.Conn{}
// nft delete table inet fail2drop
conn.DelTable(&nf.Table{Name: "fail2drop"})
conn.Flush()
fail2drop := &nf.Table{
Family: nf.TableFamilyINet,
Name: "fail2drop",
}
// nft add table inet fail2drop
fail2drop = conn.AddTable(fail2drop)
// nft add chain inet fail2drop FAIL2DROP
chain := &nf.Chain{
Name: "FAIL2DROP",
Table: fail2drop,
Type: nf.ChainTypeFilter,
Hooknum: nf.ChainHookPrerouting,
Priority: nf.ChainPriorityRaw,
}
chain = conn.AddChain(chain)
conn.Flush()
}
func install() {
// Write the binary if not in PATH
exec.Command("systemctl", "stop", name).Run()
bin, err := os.ReadFile(os.Args[0])
if err == nil {
err = os.WriteFile(prefix+name, bin, 0755)
if err != nil {
if errors.Is(err, syscall.EACCES) || errors.Is(err, syscall.ETXTBSY) {
log.Fatalln("insufficient permissions, run with root privileges")
}
log.Fatalln(err)
}
os.Chown(prefix+name, 0, 0)
}
var f *os.File
f, err = os.OpenFile(config, os.O_CREATE|os.O_EXCL|os.O_WRONLY, 0644)
if err == nil {
f.WriteString(cfgtmpl)
}
f.Close()
f, err = os.Create(unitname)
if err != nil {
log.Fatalln(err, "could not create systemd unit file "+unitname)
}
exec.Command("systemctl", "stop", name).Run()
_, err = f.WriteString(fmt.Sprintf(unittmpl, name, version, name, varlog, varlog))
f.Close()
if err != nil {
log.Fatalln(err, "could not instantiate systemd unit file "+unitname)
}
err = exec.Command("systemctl", "daemon-reload").Run()
if err != nil {
log.Fatalln(err, "could not reload the systemd service daemons")
}
err = exec.Command("systemctl", "start", name).Run()
if err != nil {
log.Fatalln(err, "could not start systemd service "+name)
}
err = exec.Command("systemctl", "enable", name).Run()
if err != nil {
log.Fatalln(err, "could not enable systemd service "+name)
}
os.Exit(0)
}
func uninstall() {
exec.Command("systemctl", "stop", name).Run()
exec.Command("systemctl", "disable", name).Run()
err := os.Remove(unitname)
if err != nil && !errors.Is(err, syscall.ENOENT) {
log.Fatalln(err, "failure to remove unit file "+unitname)
}
os.Exit(0)
}
func main() {
if len(os.Args) > 2 {
usage("Too many arguments")
}
doinstall, given := false, false
if len(os.Args) > 1 {
switch os.Args[1] {
case "help", "-h", "--help":
usage("")
case "version", "-V", "--version":
fmt.Println(name + " v" + version)
os.Exit(0)
case "uninstall", "-u", "--uninstall":
uninstall()
case "install", "-i", "--install":
doinstall = true
case "noaction", "-n", "--noaction", "check", "-c", "--check":
noaction, once = true, true
case "once", "-o", "--once":
once = true
default:
config = os.Args[1]
given = true
}
}
var cfgdata []byte
var err error
if given { // If specified, only use that as config source
cfgdata, err = os.ReadFile(config)
if err != nil {
log.Fatalln("Given configfile not found: " + config)
}
} else { // If not specified, check PWD
cfgdata, err = os.ReadFile(name + ".yml")
if err != nil { // If not in PWD, check /etc
cfgdata, err = os.ReadFile(config)
if err != nil {
if doinstall {
install()
}
log.Println("No configfile '" + name + ".yml' found in the current directory,")
log.Fatalln("nor at the default location: " + config)
}
}
}
var cfg interface{}
err = yaml.Unmarshal(cfgdata, &cfg)
if err != nil {
log.Fatalln("syntax error in the configfile: " + config)
}
cfgslice := cfg.(map[string]interface{})
if doinstall {
l, ok := cfgslice["varlog"]
if ok {
varlog = l.(string)
}
install()
}
initnf()
var logsearches []logsearch
for key, value := range cfgslice {
switch key {
case "varlog":
varlog = value.(string)
case "whitelist":
if value != nil {
for _, ip := range value.([]interface{}) {
whitelist = append(whitelist, ip.(string))
}
}
default:
var logsearch logsearch
logsearch.set = key
count := 0
values := value.(map[string]interface{})
for k, v := range values {
switch k {
case "logfile":
logsearch.logfile = v.(string)
count += 1
case "tag":
logsearch.tag = v.(string)
count += 1
case "ipregex":
logsearch.ipregex = v.(string)
count += 1
case "bancount":
logsearch.bancount = v.(int)
count += 1
}
}
if count == 4 { // All 4 properties are needed
logsearches = append(logsearches, logsearch)
}
}
}
for _, logsearch := range logsearches {
wg.Add(1)
go follow(logsearch)
}
wg.Wait()
}