cmd/stepd: Add privelege dropping

cmd/stepd/main.go

@@ -6,7 +6,11 @@ import "log"
 import "time"
 import "slices"
 import "errors"
+import "syscall"
+import "os/user"
 import "context"
+import "strings"
+import "strconv"
 import "net/http"
 import "unicode/utf8"
 import "path/filepath"
@@ -27,6 +31,10 @@ func main () {
 		'p', "pid-file",
 		"Write the PID to the specified file",
 		"", cli.ValString)
+	flagUser := cli.NewInputFlag (
+		'u', "user",
+		"The user:group to run as",
+		"", cli.ValString)
 	flagLogDirectory := cli.NewInputFlag (
 		'l', "log-directory",
 		"Write logs to the specified directory",
@@ -52,6 +60,7 @@ func main () {
 	cmd := cli.New (
 		"Run an HTTP server that automaticaly executes STEP files",
 		flagPidFile,
+		flagUser,
 		flagLogDirectory,
 		flagHTTPAddress,
 		flagHTTPErrorDocument,
@@ -98,11 +107,15 @@ func main () {
 		if err != nil { log.Fatalln("XXX", err) }
 		pidFile := daemon.PidFile(pidFileAbs)
 		err = pidFile.Start()
-		if err != nil { log.Println("!!! could not write pid:", err) }
-		defer func () {
-			err := pidFile.Close()
-			if err != nil { log.Println("!!! could not delete pidfile:", err) }
-		} ()
+		if err != nil { log.Fatalln("XXX could not write pid:", err) }
+	}
+
+	// drop privelege
+	if flagUser.Value != "" {
+		log.Println("... dropping privelege to", flagUser.Value)
+		user, group, _ := strings.Cut(flagUser.Value, ":")
+		err := dropPrivelege(user, group)
+		if err != nil { log.Fatalln("XXX could not drop privelege:", err) }
 	}
 
 	// the single argument is for the directory to serve. we actually cd
@@ -259,3 +272,23 @@ func logProviders (providers []step.Provider) {
 	}
 	line()
 }
+
+func dropPrivelege (usr, group string) error {
+	if group != "" {
+		groupInfo, err := user.LookupGroup(group)
+		if err != nil { return err }
+		gid, err := strconv.Atoi(groupInfo.Gid)
+		if err != nil { return err }
+		err = syscall.Setgid(gid)
+		if err != nil { return err }
+	}
+	if usr != "" {
+		usrInfo, err := user.Lookup(usr)
+		if err != nil { return err }
+		uid, err := strconv.Atoi(usrInfo.Uid)
+		if err != nil { return err }
+		err = syscall.Setuid(uid)
+		if err != nil { return err }
+	}
+	return nil
+}