mirror of
https://codeberg.org/forgejo/forgejo
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311 lines
9.2 KiB
Go
311 lines
9.2 KiB
Go
// Copyright 2021 The Gitea Authors. All rights reserved.
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// Use of this source code is governed by a MIT-style
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// license that can be found in the LICENSE file.
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package models
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import (
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"crypto/rsa"
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"crypto/x509"
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"encoding/asn1"
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"encoding/base64"
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"encoding/binary"
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"encoding/pem"
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"errors"
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"fmt"
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"math/big"
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"os"
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"strconv"
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"strings"
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"code.gitea.io/gitea/modules/log"
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"code.gitea.io/gitea/modules/process"
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"code.gitea.io/gitea/modules/setting"
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"code.gitea.io/gitea/modules/util"
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"golang.org/x/crypto/ssh"
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)
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// ____ __. __________
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// | |/ _|____ ___.__. \______ \_____ _______ ______ ___________
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// | <_/ __ < | | | ___/\__ \\_ __ \/ ___// __ \_ __ \
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// | | \ ___/\___ | | | / __ \| | \/\___ \\ ___/| | \/
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// |____|__ \___ > ____| |____| (____ /__| /____ >\___ >__|
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// \/ \/\/ \/ \/ \/
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//
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// This file contains functiosn for parsing ssh-keys
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//
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// TODO: Consider if these functions belong in models - no other models function call them or are called by them
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// They may belong in a service or a module
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const ssh2keyStart = "---- BEGIN SSH2 PUBLIC KEY ----"
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func extractTypeFromBase64Key(key string) (string, error) {
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b, err := base64.StdEncoding.DecodeString(key)
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if err != nil || len(b) < 4 {
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return "", fmt.Errorf("invalid key format: %v", err)
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}
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keyLength := int(binary.BigEndian.Uint32(b))
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if len(b) < 4+keyLength {
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return "", fmt.Errorf("invalid key format: not enough length %d", keyLength)
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}
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return string(b[4 : 4+keyLength]), nil
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}
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// parseKeyString parses any key string in OpenSSH or SSH2 format to clean OpenSSH string (RFC4253).
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func parseKeyString(content string) (string, error) {
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// remove whitespace at start and end
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content = strings.TrimSpace(content)
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var keyType, keyContent, keyComment string
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if strings.HasPrefix(content, ssh2keyStart) {
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// Parse SSH2 file format.
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// Transform all legal line endings to a single "\n".
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content = strings.NewReplacer("\r\n", "\n", "\r", "\n").Replace(content)
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lines := strings.Split(content, "\n")
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continuationLine := false
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for _, line := range lines {
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// Skip lines that:
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// 1) are a continuation of the previous line,
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// 2) contain ":" as that are comment lines
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// 3) contain "-" as that are begin and end tags
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if continuationLine || strings.ContainsAny(line, ":-") {
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continuationLine = strings.HasSuffix(line, "\\")
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} else {
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keyContent += line
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}
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}
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t, err := extractTypeFromBase64Key(keyContent)
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if err != nil {
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return "", fmt.Errorf("extractTypeFromBase64Key: %v", err)
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}
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keyType = t
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} else {
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if strings.Contains(content, "-----BEGIN") {
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// Convert PEM Keys to OpenSSH format
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// Transform all legal line endings to a single "\n".
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content = strings.NewReplacer("\r\n", "\n", "\r", "\n").Replace(content)
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block, _ := pem.Decode([]byte(content))
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if block == nil {
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return "", fmt.Errorf("failed to parse PEM block containing the public key")
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}
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pub, err := x509.ParsePKIXPublicKey(block.Bytes)
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if err != nil {
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var pk rsa.PublicKey
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_, err2 := asn1.Unmarshal(block.Bytes, &pk)
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if err2 != nil {
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return "", fmt.Errorf("failed to parse DER encoded public key as either PKIX or PEM RSA Key: %v %v", err, err2)
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}
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pub = &pk
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}
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sshKey, err := ssh.NewPublicKey(pub)
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if err != nil {
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return "", fmt.Errorf("unable to convert to ssh public key: %v", err)
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}
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content = string(ssh.MarshalAuthorizedKey(sshKey))
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}
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// Parse OpenSSH format.
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// Remove all newlines
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content = strings.NewReplacer("\r\n", "", "\n", "").Replace(content)
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parts := strings.SplitN(content, " ", 3)
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switch len(parts) {
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case 0:
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return "", errors.New("empty key")
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case 1:
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keyContent = parts[0]
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case 2:
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keyType = parts[0]
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keyContent = parts[1]
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default:
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keyType = parts[0]
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keyContent = parts[1]
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keyComment = parts[2]
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}
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// If keyType is not given, extract it from content. If given, validate it.
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t, err := extractTypeFromBase64Key(keyContent)
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if err != nil {
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return "", fmt.Errorf("extractTypeFromBase64Key: %v", err)
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}
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if len(keyType) == 0 {
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keyType = t
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} else if keyType != t {
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return "", fmt.Errorf("key type and content does not match: %s - %s", keyType, t)
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}
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}
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// Finally we need to check whether we can actually read the proposed key:
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_, _, _, _, err := ssh.ParseAuthorizedKey([]byte(keyType + " " + keyContent + " " + keyComment))
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if err != nil {
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return "", fmt.Errorf("invalid ssh public key: %v", err)
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}
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return keyType + " " + keyContent + " " + keyComment, nil
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}
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// CheckPublicKeyString checks if the given public key string is recognized by SSH.
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// It returns the actual public key line on success.
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func CheckPublicKeyString(content string) (_ string, err error) {
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if setting.SSH.Disabled {
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return "", ErrSSHDisabled{}
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}
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content, err = parseKeyString(content)
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if err != nil {
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return "", err
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}
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content = strings.TrimRight(content, "\n\r")
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if strings.ContainsAny(content, "\n\r") {
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return "", errors.New("only a single line with a single key please")
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}
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// remove any unnecessary whitespace now
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content = strings.TrimSpace(content)
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if !setting.SSH.MinimumKeySizeCheck {
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return content, nil
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}
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var (
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fnName string
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keyType string
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length int
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)
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if setting.SSH.StartBuiltinServer {
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fnName = "SSHNativeParsePublicKey"
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keyType, length, err = SSHNativeParsePublicKey(content)
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} else {
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fnName = "SSHKeyGenParsePublicKey"
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keyType, length, err = SSHKeyGenParsePublicKey(content)
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}
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if err != nil {
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return "", fmt.Errorf("%s: %v", fnName, err)
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}
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log.Trace("Key info [native: %v]: %s-%d", setting.SSH.StartBuiltinServer, keyType, length)
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if minLen, found := setting.SSH.MinimumKeySizes[keyType]; found && length >= minLen {
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return content, nil
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} else if found && length < minLen {
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return "", fmt.Errorf("key length is not enough: got %d, needs %d", length, minLen)
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}
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return "", fmt.Errorf("key type is not allowed: %s", keyType)
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}
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// SSHNativeParsePublicKey extracts the key type and length using the golang SSH library.
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func SSHNativeParsePublicKey(keyLine string) (string, int, error) {
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fields := strings.Fields(keyLine)
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if len(fields) < 2 {
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return "", 0, fmt.Errorf("not enough fields in public key line: %s", keyLine)
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}
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raw, err := base64.StdEncoding.DecodeString(fields[1])
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if err != nil {
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return "", 0, err
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}
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pkey, err := ssh.ParsePublicKey(raw)
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if err != nil {
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if strings.Contains(err.Error(), "ssh: unknown key algorithm") {
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return "", 0, ErrKeyUnableVerify{err.Error()}
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}
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return "", 0, fmt.Errorf("ParsePublicKey: %v", err)
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}
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// The ssh library can parse the key, so next we find out what key exactly we have.
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switch pkey.Type() {
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case ssh.KeyAlgoDSA:
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rawPub := struct {
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Name string
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P, Q, G, Y *big.Int
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}{}
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if err := ssh.Unmarshal(pkey.Marshal(), &rawPub); err != nil {
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return "", 0, err
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}
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// as per https://bugzilla.mindrot.org/show_bug.cgi?id=1647 we should never
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// see dsa keys != 1024 bit, but as it seems to work, we will not check here
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return "dsa", rawPub.P.BitLen(), nil // use P as per crypto/dsa/dsa.go (is L)
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case ssh.KeyAlgoRSA:
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rawPub := struct {
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Name string
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E *big.Int
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N *big.Int
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}{}
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if err := ssh.Unmarshal(pkey.Marshal(), &rawPub); err != nil {
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return "", 0, err
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}
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return "rsa", rawPub.N.BitLen(), nil // use N as per crypto/rsa/rsa.go (is bits)
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case ssh.KeyAlgoECDSA256:
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return "ecdsa", 256, nil
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case ssh.KeyAlgoECDSA384:
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return "ecdsa", 384, nil
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case ssh.KeyAlgoECDSA521:
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return "ecdsa", 521, nil
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case ssh.KeyAlgoED25519:
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return "ed25519", 256, nil
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case ssh.KeyAlgoSKECDSA256:
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return "ecdsa-sk", 256, nil
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case ssh.KeyAlgoSKED25519:
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return "ed25519-sk", 256, nil
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}
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return "", 0, fmt.Errorf("unsupported key length detection for type: %s", pkey.Type())
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}
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// writeTmpKeyFile writes key content to a temporary file
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// and returns the name of that file, along with any possible errors.
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func writeTmpKeyFile(content string) (string, error) {
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tmpFile, err := os.CreateTemp(setting.SSH.KeyTestPath, "gitea_keytest")
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if err != nil {
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return "", fmt.Errorf("TempFile: %v", err)
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}
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defer tmpFile.Close()
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if _, err = tmpFile.WriteString(content); err != nil {
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return "", fmt.Errorf("WriteString: %v", err)
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}
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return tmpFile.Name(), nil
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}
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// SSHKeyGenParsePublicKey extracts key type and length using ssh-keygen.
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func SSHKeyGenParsePublicKey(key string) (string, int, error) {
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tmpName, err := writeTmpKeyFile(key)
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if err != nil {
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return "", 0, fmt.Errorf("writeTmpKeyFile: %v", err)
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}
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defer func() {
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if err := util.Remove(tmpName); err != nil {
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log.Warn("Unable to remove temporary key file: %s: Error: %v", tmpName, err)
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}
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}()
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stdout, stderr, err := process.GetManager().Exec("SSHKeyGenParsePublicKey", setting.SSH.KeygenPath, "-lf", tmpName)
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if err != nil {
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return "", 0, fmt.Errorf("fail to parse public key: %s - %s", err, stderr)
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}
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if strings.Contains(stdout, "is not a public key file") {
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return "", 0, ErrKeyUnableVerify{stdout}
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}
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fields := strings.Split(stdout, " ")
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if len(fields) < 4 {
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return "", 0, fmt.Errorf("invalid public key line: %s", stdout)
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}
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keyType := strings.Trim(fields[len(fields)-1], "()\r\n")
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length, err := strconv.ParseInt(fields[0], 10, 32)
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if err != nil {
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return "", 0, err
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}
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return strings.ToLower(keyType), int(length), nil
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}
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