Implement drop privileges

Author: esamattis

config_test.yml

@@ -1,4 +1,5 @@
 port: 1234
+# user: hooktftp
 hooks:
 
   - name: Shell hook

drop_privileges.go

@@ -0,0 +1,43 @@
+package main
+
+import (
+	"os/user"
+	"strconv"
+	"syscall"
+)
+
+func DropPrivileges(username string) error {
+	userInfo, err := user.Lookup(username)
+	if err != nil {
+		return err
+	}
+
+	uid, err := strconv.Atoi(userInfo.Uid)
+	if err != nil {
+		return err
+	}
+
+	gid, err := strconv.Atoi(userInfo.Gid)
+	if err != nil {
+		return err
+	}
+
+	// TODO: should set secondary groups too
+	err = syscall.Setgroups([]int{gid})
+	if err != nil {
+		return err
+	}
+
+	err = syscall.Setgid(gid)
+	if err != nil {
+		return err
+	}
+
+	err = syscall.Setuid(uid)
+	if err != nil {
+		return err
+	}
+
+	return nil
+}
+

hooktftp.go

@@ -10,6 +10,8 @@ import (
 	"io/ioutil"
 	"net"
 	"os"
+	"os/user"
+	"syscall"
 	"time"
 )
 
@@ -154,6 +156,22 @@ func main() {
 
 	fmt.Println("Listening on", conf.Port)
 
+	if conf.User != "" {
+		err := DropPrivileges(conf.User)
+		if err != nil {
+			fmt.Printf("Failed to drop privileges to '%s' error: %v", conf.User, err)
+			return
+		}
+		currentUser, _ := user.Current()
+		fmt.Println("Dropped privileges to", currentUser)
+	}
+
+	if conf.User == "" && syscall.Getuid() == 0 {
+		fmt.Println("!!!!!!!!!")
+		fmt.Println("WARNING: Running as root and 'user' is not set in", CONFIG_PATH)
+		fmt.Println("!!!!!!!!!")
+	}
+
 	for {
 		res, err := server.Accept()
 		if err != nil {