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extensions.go
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extensions.go
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package tls
import (
"fmt"
"strconv"
"github.com/elastic/beats/libbeat/common"
"github.com/elastic/beats/libbeat/logp"
)
type extensionParser func(reader bufferView) interface{}
type extension struct {
label string
parser extensionParser
}
var (
// returned when the extension should go into the unparsed section
notParsedExtension interface{}
// Returned when the extension should have its own entry without a value
emptyExtension = ""
)
var extensionMap = map[uint16]extension{
0: {"server_name_indication", parseSni},
1: {"max_fragment_length", parseMaxFragmentLen},
2: {"client_certificate_url", expectEmpty},
3: {"trusted_ca_keys", ignoreContent},
4: {"truncated_hmac", expectEmpty},
5: {"status_request", ignoreContent},
6: {"user_mapping", ignoreContent},
7: {"client_authz", ignoreContent},
8: {"server_authz", ignoreContent},
9: {"cert_type", parseCertType},
10: {"supported_groups", parseSupportedGroups},
11: {"ec_points_formats", parseEcPoints},
12: {"srp", parseSrp},
13: {"signature_algorithms", parseSignatureSchemes},
16: {"application_layer_protocol_negotiation", parseALPN},
35: {"session_ticket", parseTicket},
0xff01: {"renegotiation_info", ignoreContent},
}
func parseExtensions(buffer bufferView) common.MapStr {
var extensionsLength uint16
if !buffer.read16Net(0, &extensionsLength) || extensionsLength == 0 {
// No extensions
return nil
}
limit := 2 + int(extensionsLength)
result := common.MapStr{}
var unknown []string
for base := 2; base < limit; {
var code, length uint16
if !buffer.read16Net(base, &code) || !buffer.read16Net(base+2, &length) {
logp.Warn("failed parsing extensions")
return nil
}
label, content := parseExtension(code, buffer.subview(base+4, int(length)))
if content != notParsedExtension {
result[label] = content
} else {
unknown = append(unknown, label)
}
base += 4 + int(length)
}
if len(unknown) != 0 {
result["_unparsed_"] = unknown
}
return result
}
func parseExtension(code uint16, buffer bufferView) (string, interface{}) {
if ext, ok := extensionMap[code]; ok {
return ext.label, ext.parser(buffer)
}
return strconv.Itoa(int(code)), nil
}
func parseSni(buffer bufferView) interface{} {
var listLength uint16
if !buffer.read16Net(0, &listLength) {
return notParsedExtension
}
var hosts []string
for pos, limit := 2, 2+int(listLength); pos+3 <= limit; {
var nameType uint8
var nameLen uint16
var host string
if !buffer.read8(pos, &nameType) || !buffer.read16Net(pos+1, &nameLen) ||
limit < pos+3+int(nameLen) || !buffer.readString(pos+3, int(nameLen), &host) {
logp.Warn("SNI hostname list truncated")
break
}
if nameType == 0 {
hosts = append(hosts, host)
}
pos += 3 + int(nameLen)
}
return hosts
}
func parseMaxFragmentLen(buffer bufferView) interface{} {
var val uint8
if buffer.length() == 1 && buffer.read8(0, &val) {
if val > 0 && val < 5 {
return fmt.Sprintf("2^%d", 8+val)
}
return fmt.Sprintf("(unknown:%d)", val)
}
return notParsedExtension
}
func ignoreContent(_ bufferView) interface{} {
return notParsedExtension
}
func expectEmpty(buffer bufferView) interface{} {
if buffer.length() != 0 {
return fmt.Sprintf("(expected empty: found %d bytes)", buffer.length())
}
return emptyExtension
}
func parseCertType(buffer bufferView) interface{} {
var value uint8
var types []string
pos, limit := 0, buffer.length()
if limit > 1 {
buffer.read8(0, &value)
pos = 1
if int(value)+1 < limit {
limit = 1 + int(value)
}
}
for ; pos < limit && buffer.read8(pos, &value); pos++ {
var label string
switch value {
case 0:
label = "X.509"
case 1:
label = "OpenPGP"
case 2:
label = "RawPubKey"
default:
label = fmt.Sprintf("(unknown:%d)", value)
}
types = append(types, label)
}
return types
}
func parseSupportedGroups(buffer bufferView) interface{} {
var value uint16
if !buffer.read16Net(0, &value) || int(value)+2 != buffer.length() {
return notParsedExtension
}
var groups []string
for pos := 0; buffer.read16Net(pos+2, &value); pos += 2 {
groups = append(groups, pointsGroup(value).String())
}
return groups
}
func parseEcPoints(buffer bufferView) interface{} {
var value, length uint8
if !buffer.read8(0, &length) || int(length)+1 != buffer.length() {
return notParsedExtension
}
var formats []string
for pos := 0; pos < int(length) && buffer.read8(1+pos, &value); pos++ {
formats = append(formats, ecPointsFormat(value).String())
}
return formats
}
func parseSrp(buffer bufferView) interface{} {
var length uint8
if !buffer.read8(0, &length) || int(length)+1 > buffer.length() {
return notParsedExtension
}
var user string
if !buffer.readString(1, int(length), &user) {
return notParsedExtension
}
return user
}
func parseSignatureSchemes(buffer bufferView) interface{} {
var value uint16
if !buffer.read16Net(0, &value) || int(value)+2 != buffer.length() {
return notParsedExtension
}
var groups []string
for pos := 2; buffer.read16Net(pos, &value); pos += 2 {
groups = append(groups, signatureScheme(value).String())
}
return groups
}
func parseTicket(buffer bufferView) interface{} {
if buffer.length() > 0 {
return fmt.Sprintf("(%d bytes)", buffer.length())
}
return emptyExtension
}
func parseALPN(buffer bufferView) interface{} {
var length uint16
if !buffer.read16Net(0, &length) || int(length)+2 != buffer.length() {
return notParsedExtension
}
var strlen uint8
var proto string
var protos []string
for pos := 2; buffer.read8(pos, &strlen); {
if !buffer.readString(pos+1, int(strlen), &proto) {
return notParsedExtension
}
protos = append(protos, proto)
pos += 1 + int(strlen)
}
return protos
}