revert deleted file

plugin/internal/workingdir/workingdir.go

@@ -0,0 +1,166 @@
+package workingdir
+
+import (
+	"bufio"
+	"crypto/subtle"
+	"fmt"
+	"os"
+	"path"
+	"regexp"
+	"strings"
+
+	"github.com/tg123/sshpiper/libplugin"
+	"golang.org/x/crypto/ssh"
+
+	log "github.com/sirupsen/logrus"
+)
+
+type Workingdir struct {
+	Path        string
+	NoCheckPerm bool
+	Strict      bool
+}
+
+var (
+	usernameRule *regexp.Regexp
+)
+
+const (
+	userAuthorizedKeysFile = "authorized_keys"
+	userKeyFile            = "id_rsa"
+	userUpstreamFile       = "sshpiper_upstream"
+	userKnownHosts         = "known_hosts"
+)
+
+func init() {
+	// Base username validation on Debians default: https://sources.debian.net/src/adduser/3.113%2Bnmu3/adduser.conf/#L85
+	// -> NAME_REGEX="^[a-z][-a-z0-9_]*\$"
+	// The length is limited to 32 characters. See man 8 useradd: https://linux.die.net/man/8/useradd
+	usernameRule, _ = regexp.Compile("^[a-z_][-a-z0-9_]{0,31}$")
+}
+
+func IsUsernameSecure(user string) bool {
+	return usernameRule.MatchString(user)
+}
+
+func (w *Workingdir) Mapkey(pub []byte) ([]byte, error) {
+
+	var rest []byte
+	rest, err := w.Readfile(userAuthorizedKeysFile)
+	if err != nil {
+		return nil, err
+	}
+
+	var authedPubkey ssh.PublicKey
+
+	for len(rest) > 0 {
+		authedPubkey, _, _, rest, err = ssh.ParseAuthorizedKey(rest)
+
+		if err != nil {
+			return nil, err
+		}
+
+		if subtle.ConstantTimeCompare(authedPubkey.Marshal(), pub) == 1 {
+			log.Infof("found mapping key %v", w.fullpath(userKeyFile))
+			return w.Readfile(userKeyFile)
+		}
+	}
+
+	return nil, fmt.Errorf("no matching key found")
+}
+
+func (w *Workingdir) CreateUpstream() (*libplugin.Upstream, error) {
+
+	data, err := w.Readfile(userUpstreamFile)
+	if err != nil {
+		return nil, err
+	}
+
+	host, port, user, err := parseUpstreamFile(string(data))
+	if err != nil {
+		return nil, err
+	}
+
+	return &libplugin.Upstream{
+		Host:          host,
+		Port:          int32(port),
+		UserName:      user,
+		IgnoreHostKey: !w.Strict,
+	}, nil
+}
+
+func (w *Workingdir) VerifyHostKey(hostname, netaddr string, key []byte) error {
+	if !w.Strict {
+		return nil
+	}
+
+	f, err := os.Open(w.fullpath(userKnownHosts))
+	if err != nil {
+		return err
+	}
+	defer f.Close()
+
+	return libplugin.VerifyHostKeyFromKnownHosts(f, hostname, netaddr, key)
+}
+
+func (w *Workingdir) checkPerm(file string) error {
+	filename := path.Join(w.Path, file)
+	f, err := os.Open(filename)
+	if err != nil {
+		return err
+	}
+	defer f.Close()
+
+	fi, err := f.Stat()
+	if err != nil {
+		return err
+	}
+
+	if w.NoCheckPerm {
+		return nil
+	}
+
+	if fi.Mode().Perm()&0077 != 0 {
+		return fmt.Errorf("%v's perm is too open", filename)
+	}
+
+	return nil
+}
+
+func (w *Workingdir) fullpath(file string) string {
+	return path.Join(w.Path, file)
+}
+
+func (w *Workingdir) Readfile(file string) ([]byte, error) {
+	if err := w.checkPerm(file); err != nil {
+		return nil, err
+	}
+
+	return os.ReadFile(w.fullpath(file))
+}
+
+func parseUpstreamFile(data string) (host string, port int, user string, err error) {
+	r := bufio.NewReader(strings.NewReader(data))
+	for {
+		host, err = r.ReadString('\n')
+		if err != nil {
+			break
+		}
+
+		host = strings.TrimSpace(host)
+
+		if host != "" && host[0] != '#' {
+			break
+		}
+	}
+
+	t := strings.SplitN(host, "@", 2)
+
+	if len(t) > 1 {
+		user = t[0]
+		host = t[1]
+	}
+
+	host, port, err = libplugin.SplitHostPortForSSH(host)
+	return
+}