[client] Use setsid to avoid the parent process from being killed via HUP by login (#4900)

client/ssh/server/command_execution_unix.go

@@ -10,6 +10,7 @@ import (
 	"os"
 	"os/exec"
 	"os/user"
+	"runtime"
 	"strings"
 	"sync"
 	"syscall"
@@ -75,6 +76,29 @@ func (s *Server) detectSuPtySupport(ctx context.Context) bool {
 	return supported
 }
 
+// detectUtilLinuxLogin checks if login is from util-linux (vs shadow-utils).
+// util-linux login uses vhangup() which requires setsid wrapper to avoid killing parent.
+// See https://bugs.debian.org/1078023 for details.
+func (s *Server) detectUtilLinuxLogin(ctx context.Context) bool {
+	if runtime.GOOS != "linux" {
+		return false
+	}
+
+	ctx, cancel := context.WithTimeout(ctx, 500*time.Millisecond)
+	defer cancel()
+
+	cmd := exec.CommandContext(ctx, "login", "--version")
+	output, err := cmd.CombinedOutput()
+	if err != nil {
+		log.Debugf("login --version failed (likely shadow-utils): %v", err)
+		return false
+	}
+
+	isUtilLinux := strings.Contains(string(output), "util-linux")
+	log.Debugf("util-linux login detected: %v", isUtilLinux)
+	return isUtilLinux
+}
+
 // createSuCommand creates a command using su -l -c for privilege switching
 func (s *Server) createSuCommand(session ssh.Session, localUser *user.User, hasPty bool) (*exec.Cmd, error) {
 	suPath, err := exec.LookPath("su")
@@ -144,7 +168,7 @@ func (s *Server) handlePty(logger *log.Entry, session ssh.Session, privilegeResu
 		return false
 	}
 
-	logger.Infof("starting interactive shell: %s", execCmd.Path)
+	logger.Infof("starting interactive shell: %s", strings.Join(execCmd.Args, " "))
 	return s.runPtyCommand(logger, session, execCmd, ptyReq, winCh)
 }