gomonop/cmd/sslcert/main.go

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package sslcert // import nocternity.net/gomonop/cmd/sslcert
import (
"bufio"
"crypto/tls"
"crypto/x509"
"fmt"
"net"
"net/textproto"
"os"
"strconv"
"strings"
"time"
"github.com/karrick/golf"
"nocternity.net/gomonop/pkg/perfdata"
"nocternity.net/gomonop/pkg/plugin"
"nocternity.net/gomonop/pkg/program"
)
//--------------------------------------------------------------------------------------------------------
// Interface that can be implemented to fetch TLS certificates.
type certGetter interface {
getCertificate(tlsConfig *tls.Config, address string) (*x509.Certificate, error)
}
// Full TLS certificate fetcher.
type fullTLSGetter struct{}
func (f fullTLSGetter) getCertificate(tlsConfig *tls.Config, address string) (*x509.Certificate, error) {
conn, err := tls.Dial("tcp", address, tlsConfig)
if err != nil {
return nil, err
}
defer conn.Close()
if err := conn.Handshake(); err != nil {
return nil, err
}
return conn.ConnectionState().PeerCertificates[0], nil
}
// SMTP+STARTTLS certificate getter.
type smtpGetter struct{}
func (f smtpGetter) cmd(tcon *textproto.Conn, expectCode int, text string) error {
id, err := tcon.Cmd("%s", text)
if err != nil {
return err
}
tcon.StartResponse(id)
defer tcon.EndResponse(id)
_, _, err = tcon.ReadResponse(expectCode)
return err
}
func (f smtpGetter) getCertificate(tlsConfig *tls.Config, address string) (*x509.Certificate, error) {
conn, err := net.Dial("tcp", address)
if err != nil {
return nil, err
}
text := textproto.NewConn(conn)
defer text.Close()
if _, _, err := text.ReadResponse(220); err != nil {
return nil, err
}
if err := f.cmd(text, 250, "HELO localhost"); err != nil {
return nil, err
}
if err := f.cmd(text, 220, "STARTTLS"); err != nil {
return nil, err
}
t := tls.Client(conn, tlsConfig)
if err := t.Handshake(); err != nil {
return nil, err
}
return t.ConnectionState().PeerCertificates[0], nil
}
// ManageSieve STARTTLS certificate getter.
type sieveGetter struct{}
type sieveError struct {
msg string
}
func (e sieveError) Error() string {
return "Sieve error: " + e.msg
}
func (f sieveGetter) waitOK(conn net.Conn) error {
scanner := bufio.NewScanner(conn)
for scanner.Scan() {
line := scanner.Text()
if strings.HasPrefix(line, "OK") {
return nil
}
if strings.HasPrefix(line, "NO ") {
return sieveError{msg: line[3:]}
}
if strings.HasPrefix(line, "BYE ") {
return sieveError{msg: line[4:]}
}
}
return scanner.Err()
}
func (f sieveGetter) runCmd(conn net.Conn, cmd string) error {
if _, err := fmt.Fprintf(conn, "%s\r\n", cmd); err != nil {
return err
}
return f.waitOK(conn)
}
func (f sieveGetter) getCertificate(tlsConfig *tls.Config, address string) (*x509.Certificate, error) {
conn, err := net.Dial("tcp", address)
if err != nil {
return nil, err
}
defer conn.Close()
if err := f.waitOK(conn); err != nil {
return nil, err
}
if err := f.runCmd(conn, "STARTTLS"); err != nil {
return nil, err
}
t := tls.Client(conn, tlsConfig)
if err := t.Handshake(); err != nil {
return nil, err
}
return t.ConnectionState().PeerCertificates[0], nil
}
// Supported StartTLS protocols.
var certGetters = map[string]certGetter{
"": fullTLSGetter{},
"smtp": &smtpGetter{},
"sieve": &sieveGetter{},
}
// Get a string that represents supported StartTLS protocols.
func listSupportedGetters() string {
strBuilder := strings.Builder{}
for key := range certGetters {
if strBuilder.Len() != 0 {
strBuilder.WriteString(", ")
}
strBuilder.WriteString(key)
}
return strBuilder.String()
}
//--------------------------------------------------------------------------------------------------------
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// Command line flags that have been parsed.
type programFlags struct {
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hostname string // Main host name to connect to
port int // TCP port to connect to
warn int // Threshold for warning state (days)
crit int // Threshold for critical state (days)
ignoreCnOnly bool // Do not warn about SAN-less certificates
extraNames []string // Extra names the certificate should include
startTLS string // Protocol to use before requesting a switch to TLS.
}
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// Program data including configuration and runtime data.
type checkProgram struct {
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programFlags // Flags from the command line
plugin *plugin.Plugin // Plugin output state
certificate *x509.Certificate // X.509 certificate from the server
}
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// Parse command line arguments and store their values. If the -h flag is present,
// help will be displayed and the program will exit.
func (flags *programFlags) parseArguments() {
var (
names string
help bool
)
golf.BoolVarP(&help, 'h', "help", false, "Display usage information")
golf.StringVarP(&flags.hostname, 'H', "hostname", "", "Host name to connect to.")
golf.IntVarP(&flags.port, 'P', "port", -1, "Port to connect to.")
golf.IntVarP(&flags.warn, 'W', "warning", -1,
"Validity threshold below which a warning state is issued, in days.")
golf.IntVarP(&flags.crit, 'C', "critical", -1,
"Validity threshold below which a critical state is issued, in days.")
golf.BoolVar(&flags.ignoreCnOnly, "ignore-cn-only", false,
"Do not issue warnings regarding certificates that do not use SANs at all.")
golf.StringVarP(&names, 'a', "additional-names", "",
"A comma-separated list of names that the certificate should also provide.")
golf.StringVarP(&flags.startTLS, 's', "start-tls", "",
fmt.Sprintf(
"Protocol to use before requesting a switch to TLS. "+
"Supported protocols: %s.",
listSupportedGetters()))
golf.Parse()
if help {
golf.Usage()
os.Exit(0)
}
if names == "" {
flags.extraNames = make([]string, 0)
} else {
flags.extraNames = strings.Split(names, ",")
}
}
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// Initialise the monitoring check program.
func NewProgram() program.Program {
program := &checkProgram{
plugin: plugin.New("Certificate check"),
}
program.parseArguments()
return program
}
// Return the program's output value.
func (program *checkProgram) Output() *plugin.Plugin {
return program.plugin
}
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// Check the values that were specified from the command line. Returns true
// if the arguments made sense.
func (program *checkProgram) CheckArguments() bool {
if program.hostname == "" {
program.plugin.SetState(plugin.StatusUnknown, "no hostname specified")
return false
}
if program.port < 1 || program.port > 65535 {
program.plugin.SetState(plugin.StatusUnknown, "invalid or missing port number")
return false
}
if program.warn != -1 && program.crit != -1 && program.warn <= program.crit {
program.plugin.SetState(plugin.StatusUnknown, "nonsensical thresholds")
return false
}
if _, ok := certGetters[program.startTLS]; !ok {
errstr := "unsupported StartTLS protocol " + program.startTLS
program.plugin.SetState(plugin.StatusUnknown, errstr)
return false
}
program.hostname = strings.ToLower(program.hostname)
return true
}
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// Connect to the remote host and obtain the certificate. Returns an error
// if connecting or performing the TLS handshake fail.
func (program *checkProgram) getCertificate() error {
tlsConfig := &tls.Config{
//nolint:gosec // The whole point is to read the certificate.
InsecureSkipVerify: true,
MinVersion: tls.VersionTLS10,
}
connString := fmt.Sprintf("%s:%d", program.hostname, program.port)
certificate, err := certGetters[program.startTLS].getCertificate(tlsConfig, connString)
program.certificate = certificate
return err
}
// Check that the CN of a certificate that doesn't contain a SAN actually
// matches the requested host name.
func (program *checkProgram) checkSANlessCertificate() bool {
if !program.ignoreCnOnly || len(program.extraNames) != 0 {
program.plugin.SetState(plugin.StatusWarning,
"certificate doesn't have SAN domain names")
return false
}
dn := strings.ToLower(program.certificate.Subject.String())
if !strings.HasPrefix(dn, fmt.Sprintf("cn=%s,", program.hostname)) {
program.plugin.SetState(plugin.StatusCritical, "incorrect certificate CN")
return false
}
return true
}
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// Checks whether a name is listed in the certificate's DNS names. If the name
// cannot be found, a line will be added to the plugin output and false will
// be returned.
func (program *checkProgram) checkHostName(name string) bool {
for _, n := range program.certificate.DNSNames {
if strings.ToLower(n) == name {
return true
}
}
program.plugin.AddLine("missing DNS name " + name + " in certificate")
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return false
}
// Ensure the certificate matches the specified names. Returns false if it
// doesn't.
func (program *checkProgram) checkNames() bool {
if len(program.certificate.DNSNames) == 0 {
return program.checkSANlessCertificate()
}
certificateIsOk := program.checkHostName(program.hostname)
for _, name := range program.extraNames {
certificateIsOk = program.checkHostName(name) && certificateIsOk
}
if !certificateIsOk {
program.plugin.SetState(plugin.StatusCritical, "names missing from SAN domain names")
}
return certificateIsOk
}
// Check a certificate's time to expiry against the warning and critical
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// thresholds, returning a status code and description based on these
// values.
func (program *checkProgram) checkCertificateExpiry(tlDays int) (plugin.Status, string) {
if tlDays <= 0 {
return plugin.StatusCritical, "certificate expired"
}
var limitStr string
var state plugin.Status
switch {
case program.crit > 0 && tlDays <= program.crit:
limitStr = fmt.Sprintf(" (<= %d)", program.crit)
state = plugin.StatusCritical
case program.warn > 0 && tlDays <= program.warn:
limitStr = fmt.Sprintf(" (<= %d)", program.warn)
state = plugin.StatusWarning
default:
limitStr = ""
state = plugin.StatusOK
}
statusString := fmt.Sprintf("certificate will expire in %d days%s",
tlDays, limitStr)
return state, statusString
}
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// Set the plugin's performance data based on the time left before the
// certificate expires and the thresholds.
func (program *checkProgram) setPerfData(tlDays int) {
pdat := perfdata.New("validity", perfdata.UomNone, strconv.Itoa(tlDays))
if program.crit > 0 {
pdat.SetCrit(perfdata.RangeMax(strconv.Itoa(program.crit)))
}
if program.warn > 0 {
pdat.SetWarn(perfdata.RangeMax(strconv.Itoa(program.warn)))
}
program.plugin.AddPerfData(pdat)
}
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// Run the check: fetch the certificate, check its names then check its time
// to expiry and update the plugin's performance data.
func (program *checkProgram) RunCheck() {
err := program.getCertificate()
if err != nil {
program.plugin.SetState(plugin.StatusUnknown, err.Error())
} else if program.checkNames() {
timeLeft := time.Until(program.certificate.NotAfter)
tlDays := int((timeLeft + 86399*time.Second) / (24 * time.Hour))
program.plugin.SetState(program.checkCertificateExpiry(tlDays))
program.setPerfData(tlDays)
}
}