Complete overhaul

client/cmd/ssh_sftp_unix.go

@@ -0,0 +1,94 @@
+//go:build unix
+
+package cmd
+
+import (
+	"errors"
+	"io"
+	"os"
+
+	"github.com/pkg/sftp"
+	log "github.com/sirupsen/logrus"
+	"github.com/spf13/cobra"
+
+	sshserver "github.com/netbirdio/netbird/client/ssh/server"
+)
+
+var (
+	sftpUID        uint32
+	sftpGID        uint32
+	sftpGroupsInt  []uint
+	sftpWorkingDir string
+)
+
+var sshSftpCmd = &cobra.Command{
+	Use:    "sftp",
+	Short:  "SFTP server with privilege dropping (internal use)",
+	Hidden: true,
+	RunE:   sftpMain,
+}
+
+func init() {
+	sshSftpCmd.Flags().Uint32Var(&sftpUID, "uid", 0, "Target user ID")
+	sshSftpCmd.Flags().Uint32Var(&sftpGID, "gid", 0, "Target group ID")
+	sshSftpCmd.Flags().UintSliceVar(&sftpGroupsInt, "groups", nil, "Supplementary group IDs (can be repeated)")
+	sshSftpCmd.Flags().StringVar(&sftpWorkingDir, "working-dir", "", "Working directory")
+}
+
+func sftpMain(cmd *cobra.Command, _ []string) error {
+	privilegeDropper := sshserver.NewPrivilegeDropper()
+
+	var groups []uint32
+	for _, groupInt := range sftpGroupsInt {
+		groups = append(groups, uint32(groupInt))
+	}
+
+	config := sshserver.ExecutorConfig{
+		UID:        sftpUID,
+		GID:        sftpGID,
+		Groups:     groups,
+		WorkingDir: sftpWorkingDir,
+		Shell:      "",
+		Command:    "",
+	}
+
+	log.Tracef("dropping privileges for SFTP to UID=%d, GID=%d, groups=%v", config.UID, config.GID, config.Groups)
+
+	if err := privilegeDropper.DropPrivileges(config.UID, config.GID, config.Groups); err != nil {
+		cmd.PrintErrf("privilege drop failed: %v\n", err)
+		os.Exit(sshserver.ExitCodePrivilegeDropFail)
+	}
+
+	if config.WorkingDir != "" {
+		if err := os.Chdir(config.WorkingDir); err != nil {
+			cmd.PrintErrf("failed to change to working directory %s: %v\n", config.WorkingDir, err)
+		}
+	}
+
+	sftpServer, err := sftp.NewServer(struct {
+		io.Reader
+		io.WriteCloser
+	}{
+		Reader:      os.Stdin,
+		WriteCloser: os.Stdout,
+	})
+	if err != nil {
+		cmd.PrintErrf("SFTP server creation failed: %v\n", err)
+		os.Exit(sshserver.ExitCodeShellExecFail)
+	}
+
+	defer func() {
+		if err := sftpServer.Close(); err != nil {
+			cmd.PrintErrf("SFTP server close error: %v\n", err)
+		}
+	}()
+
+	log.Tracef("starting SFTP server with dropped privileges")
+	if err := sftpServer.Serve(); err != nil && !errors.Is(err, io.EOF) {
+		cmd.PrintErrf("SFTP server error: %v\n", err)
+		os.Exit(sshserver.ExitCodeShellExecFail)
+	}
+
+	os.Exit(sshserver.ExitCodeSuccess)
+	return nil
+}