Fix issues when writing files as the wrong group, whoops

main.go

@@ -3,18 +3,27 @@ package main
 import (
 	"errors"
 	"flag"
+	"fmt"
 	"github.com/buger/jsonparser"
 	"github.com/patrickmn/go-cache"
 	"github.com/pterodactyl/sftp-server/src/logger"
 	"github.com/pterodactyl/sftp-server/src/server"
 	"go.uber.org/zap"
 	"io/ioutil"
 	"os"
+	"os/user"
 	"path"
+	"runtime"
+	"strconv"
 	"time"
 )
 
 func main() {
+	if runtime.GOOS != "linux" {
+		fmt.Printf("This operating system (%s) is not supported.\n", runtime.GOOS)
+		os.Exit(1)
+	}
+
 	var (
 		configLocation   string
 		bindPort         int
@@ -41,18 +50,30 @@ func main() {
 		logger.Get().Fatalw("could not read configuration", zap.Error(err))
 	}
 
-	u, err := jsonparser.GetInt(config, "docker", "container", "user")
+	username, err := jsonparser.GetString(config, "docker", "container", "username")
 	if err != nil {
-		logger.Get().Fatalw("could not locate SFTP base user", zap.Error(err))
+		logger.Get().Debugw("could not find sftp user definition, falling back to \"pterodactyl\"", zap.Error(err))
+		username = "pterodactyl"
+	}
+
+	logger.Get().Infow("using system daemon user", zap.String("username", username))
+
+	u, err := user.Lookup(username)
+	if err != nil {
+		logger.Get().Fatalw("failed to lookup sftp user", zap.Error(err))
 		return
 	}
 
-	c := cache.New(5*time.Minute, 10*time.Minute)
+	uid, _ := strconv.Atoi(u.Uid)
+	gid, _ := strconv.Atoi(u.Gid)
 
 	var s = server.Configuration{
 		Data:  config,
-		Cache: c,
-		User:  int(u),
+		Cache: cache.New(5*time.Minute, 10*time.Minute),
+		User:  server.SftpUser{
+			Uid: uid,
+			Gid: gid,
+		},
 		Settings: server.Settings{
 			BasePath:         path.Dir(configLocation),
 			ReadOnly:         readOnlyMode,

src/server/handler.go

@@ -23,7 +23,7 @@ type FileSystem struct {
 	Permissions      []string
 	ReadOnly         bool
 	DisableDiskCheck bool
-	User             int
+	User             SftpUser
 	Cache            *cache.Cache
 	lock             sync.Mutex
 }
@@ -72,6 +72,7 @@ func (fs FileSystem) Filewrite(request *sftp.Request) (io.WriterAt, error) {
 	// If the user doesn't have enough space left on the server it should respond with an
 	// error since we won't be letting them write this file to the disk.
 	if !fs.hasSpace() {
+		logger.Get().Infow("denying file write due to space limit", zap.String("server", fs.UUID))
 		return nil, sftp.ErrSshFxFailure
 	}
 
@@ -106,7 +107,7 @@ func (fs FileSystem) Filewrite(request *sftp.Request) (io.WriterAt, error) {
 
 		// Not failing here is intentional. We still made the file, it is just owned incorrectly
 		// and will likely cause some issues.
-		if err := os.Chown(p, fs.User, fs.User); err != nil {
+		if err := os.Chown(p, fs.User.Uid, fs.User.Gid); err != nil {
 			logger.Get().Warnw("error chowning file", zap.String("file", p), zap.Error(err))
 		}
 
@@ -137,7 +138,7 @@ func (fs FileSystem) Filewrite(request *sftp.Request) (io.WriterAt, error) {
 
 	// Not failing here is intentional. We still made the file, it is just owned incorrectly
 	// and will likely cause some issues.
-	if err := os.Chown(p, fs.User, fs.User); err != nil {
+	if err := os.Chown(p, fs.User.Uid, fs.User.Gid); err != nil {
 		logger.Get().Warnw("error chowning file", zap.String("file", p), zap.Error(err))
 	}
 
@@ -248,7 +249,7 @@ func (fs FileSystem) Filecmd(request *sftp.Request) error {
 
 	// Not failing here is intentional. We still made the file, it is just owned incorrectly
 	// and will likely cause some issues.
-	if err := os.Chown(fileLocation, fs.User, fs.User); err != nil {
+	if err := os.Chown(fileLocation, fs.User.Uid, fs.User.Gid); err != nil {
 		logger.Get().Warnw("error chowning file", zap.String("file", fileLocation), zap.Error(err))
 	}
 

src/server/server.go

@@ -39,11 +39,16 @@ type Settings struct {
 	DisableDiskCheck bool
 }
 
+type SftpUser struct {
+	Uid int
+	Gid int
+}
+
 type Configuration struct {
 	Data     []byte
 	Cache    *cache.Cache
 	Settings Settings
-	User     int
+	User     SftpUser
 }
 
 type AuthenticationResponse struct {