fix(web): refuse oversized login usernames before recording them

A failed login keeps its username in the in-memory log buffer, the
limiter table and the notifier queue, and the route accepted any body
the global cap allowed. The login route now takes at most 16 KiB and
answers a username over 256 bytes with the generic failure before any
of those see it; the user setters refuse such a name too, so no stored
username can be one the login route turns away.

internal/web/controller/csrf_log_test.go

@@ -1,8 +1,11 @@
 package controller
 
 import (
+	"encoding/json"
 	"net/http"
 	"net/http/httptest"
+	"net/url"
+	"path/filepath"
 	"strings"
 	"testing"
 
@@ -10,7 +13,11 @@ import (
 	"github.com/gin-contrib/sessions/cookie"
 	"github.com/gin-gonic/gin"
 
+	"github.com/mhsanaei/3x-ui/v3/internal/database/dbtest"
 	"github.com/mhsanaei/3x-ui/v3/internal/logger"
+	"github.com/mhsanaei/3x-ui/v3/internal/web/locale"
+	"github.com/mhsanaei/3x-ui/v3/internal/web/service/panel"
+	"github.com/mhsanaei/3x-ui/v3/internal/web/session"
 )
 
 func TestLoginCSRFRejectionLogsPeerIPNotForwardedHeader(t *testing.T) {
@@ -39,3 +46,49 @@ func TestLoginCSRFRejectionLogsPeerIPNotForwardedHeader(t *testing.T) {
 		t.Fatalf("CSRF rejection log = %q, want the untrusted peer 198.51.100.9 and not the forwarded header", line)
 	}
 }
+
+// A failed login keeps its username in the log buffer, the limiter table and the
+// notifier queue; an unauthenticated caller must not be able to make that unbounded.
+func TestLoginRefusesOversizedUsernameBeforeRecordingIt(t *testing.T) {
+	gin.SetMode(gin.TestMode)
+	dbtest.InitDB(t, filepath.Join(t.TempDir(), "x-ui.db"))
+	engine := gin.New()
+	engine.Use(sessions.Sessions("3x-ui", cookie.NewStore([]byte("login-length-test-secret"))))
+	engine.Use(func(c *gin.Context) {
+		c.Set("I18n", func(_ locale.I18nType, key string, _ ...string) string { return key })
+		c.Next()
+	})
+	NewIndexController(engine.Group("/"))
+
+	tokenReq := httptest.NewRequest(http.MethodGet, "/csrf-token", nil)
+	tokenRec := httptest.NewRecorder()
+	engine.ServeHTTP(tokenRec, tokenReq)
+	var token struct{ Obj string }
+	if err := json.Unmarshal(tokenRec.Body.Bytes(), &token); err != nil || token.Obj == "" {
+		t.Fatalf("csrf token: %v %s", err, tokenRec.Body.String())
+	}
+	username := strings.Repeat("u", panel.MaxUsernameLength+1)
+	form := url.Values{"username": {username}, "password": {"wrong"}}
+	req := httptest.NewRequest(http.MethodPost, "/login", strings.NewReader(form.Encode()))
+	req.RemoteAddr = "198.51.100.10:40000"
+	req.Header.Set("Content-Type", "application/x-www-form-urlencoded")
+	req.Header.Set(session.CSRFHeaderName, token.Obj)
+	for _, cookie := range tokenRec.Result().Cookies() {
+		req.AddCookie(cookie)
+	}
+	rec := httptest.NewRecorder()
+	engine.ServeHTTP(rec, req)
+	if rec.Code != http.StatusOK || !strings.Contains(rec.Body.String(), `"success":false`) {
+		t.Fatalf("login = %d %s, want the generic failure", rec.Code, rec.Body.String())
+	}
+	for _, line := range logger.GetLogs(100, "DEBUG") {
+		if strings.Contains(line, username) {
+			t.Fatal("the oversized username reached the log buffer")
+		}
+	}
+	defaultLoginLimiter.mu.Lock()
+	defer defaultLoginLimiter.mu.Unlock()
+	if _, kept := defaultLoginLimiter.attempts[loginLimitKey("198.51.100.10", username)]; kept {
+		t.Fatal("the oversized username was kept in the limiter table")
+	}
+}

internal/web/controller/index.go

@@ -47,7 +47,8 @@ func (a *IndexController) initRouter(g *gin.RouterGroup) {
 	g.GET("/sponsors", a.sponsors)
 	g.GET("/sponsors/logo/:name", a.sponsorLogo)
 
-	g.POST("/login", middleware.CSRFMiddleware(getRemoteIp), a.login)
+	// The route carries three short fields; anything longer is refused unread.
+	g.POST("/login", middleware.MaxBodyBytes(16<<10), middleware.CSRFMiddleware(getRemoteIp), a.login)
 	g.POST("/logout", middleware.CSRFMiddleware(getRemoteIp), a.logout)
 	g.POST("/getTwoFactorEnable", middleware.CSRFMiddleware(getRemoteIp), a.getTwoFactorEnable)
 }
@@ -102,6 +103,12 @@ func (a *IndexController) login(c *gin.Context) {
 	}
 
 	remoteIP := getRemoteIp(c)
+	// No stored name is longer; the log buffer, the limiter and the notifiers keep what follows.
+	if len(form.Username) > panel.MaxUsernameLength {
+		logger.Warningf("failed login: IP=%q, reason=%q", remoteIP, "username too long")
+		pureJsonMsg(c, http.StatusOK, false, I18nWeb(c, "pages.login.toasts.wrongUsernameOrPassword"))
+		return
+	}
 	safeUser := template.HTMLEscapeString(form.Username)
 	timeStr := time.Now().Format("2006-01-02 15:04:05")
 	if blockedUntil, ok := defaultLoginLimiter.allow(remoteIP, form.Username); !ok {

internal/web/service/panel/user.go

@@ -2,6 +2,7 @@ package panel
 
 import (
 	"errors"
+	"fmt"
 	"time"
 
 	"gorm.io/gorm"
@@ -128,6 +129,9 @@ func (s *UserService) BumpLoginEpoch() error {
 }
 
 func (s *UserService) UpdateUser(id int, username string, password string) error {
+	if len(username) > MaxUsernameLength {
+		return fmt.Errorf("username can not be longer than %d bytes", MaxUsernameLength)
+	}
 	db := database.GetDB()
 	hashedPassword, err := crypto.HashPasswordAsBcrypt(password)
 	if err != nil {
@@ -157,6 +161,8 @@ func (s *UserService) UpdateUser(id int, username string, password string) error
 func (s *UserService) UpdateFirstUser(username string, password string) error {
 	if username == "" {
 		return errors.New("username can not be empty")
+	} else if len(username) > MaxUsernameLength {
+		return fmt.Errorf("username can not be longer than %d bytes", MaxUsernameLength)
 	} else if password == "" {
 		return errors.New("password can not be empty")
 	}
@@ -181,3 +187,7 @@ func (s *UserService) UpdateFirstUser(username string, password string) error {
 	user.LoginEpoch++
 	return db.Save(user).Error
 }
+
+// MaxUsernameLength bounds a panel username: the login route refuses longer names before
+// logging or recording them, so no stored name may exceed it.
+const MaxUsernameLength = 256

internal/web/service/panel/user_test.go

@@ -2,6 +2,7 @@ package panel
 
 import (
 	"path/filepath"
+	"strings"
 	"testing"
 
 	"github.com/mhsanaei/3x-ui/v3/internal/database"
@@ -48,3 +49,28 @@ func TestHasDefaultCredential(t *testing.T) {
 		})
 	}
 }
+
+// The login route refuses names over MaxUsernameLength unread, so storing one would lock
+// the admin out of their own panel.
+func TestUserSettersRefuseNamesTheLoginRouteRefuses(t *testing.T) {
+	dbtest.InitDB(t, filepath.Join(t.TempDir(), "x-ui.db"))
+	svc := &UserService{}
+	if err := svc.UpdateFirstUser("admin", "s3cret-Pass"); err != nil {
+		t.Fatalf("UpdateFirstUser: %v", err)
+	}
+	var user model.User
+	if err := database.GetDB().First(&user).Error; err != nil {
+		t.Fatalf("load user: %v", err)
+	}
+	long := strings.Repeat("a", MaxUsernameLength+1)
+	if err := svc.UpdateFirstUser(long, "s3cret-Pass"); err == nil {
+		t.Fatal("UpdateFirstUser stored a name the login route refuses")
+	}
+	if err := svc.UpdateUser(user.Id, long, "s3cret-Pass"); err == nil {
+		t.Fatal("UpdateUser stored a name the login route refuses")
+	}
+	var stored model.User
+	if err := database.GetDB().First(&stored, user.Id).Error; err != nil || stored.Username != "admin" {
+		t.Fatalf("stored username = %q (%v), want it unchanged", stored.Username, err)
+	}
+}