From 8c81ba1a782f6cbff8e4ee0043d2dc72c7df89af Mon Sep 17 00:00:00 2001
From: Harrison Healey <harrisonmhealey@gmail.com>
Date: Wed, 19 Dec 2018 09:36:39 -0500
Subject: [PATCH] MM-13526 Add validation when setting a user's Locale field
 (#10022)

---
 model/user.go      | 18 +++++++++++++++
 model/user_test.go | 56 ++++++++++++++++++++++++++++++++++++++++++++++
 2 files changed, 74 insertions(+)

diff --git a/model/user.go b/model/user.go
index 6b9bfc93dc..2db4be5d74 100644
--- a/model/user.go
+++ b/model/user.go
@@ -14,6 +14,7 @@ import (
 
 	"github.com/mattermost/mattermost-server/services/timezones"
 	"golang.org/x/crypto/bcrypt"
+	"golang.org/x/text/language"
 )
 
 const (
@@ -49,6 +50,7 @@ const (
 	USER_NAME_MAX_LENGTH      = 64
 	USER_NAME_MIN_LENGTH      = 1
 	USER_PASSWORD_MAX_LENGTH  = 72
+	USER_LOCALE_MAX_LENGTH    = 5
 )
 
 type User struct {
@@ -172,6 +174,10 @@ func (u *User) IsValid() *AppError {
 		return InvalidUserError("password_limit", u.Id)
 	}
 
+	if !IsValidLocale(u.Locale) {
+		return InvalidUserError("locale", u.Id)
+	}
+
 	return nil
 }
 
@@ -644,3 +650,15 @@ func IsValidEmailBatchingInterval(emailInterval string) bool {
 		emailInterval == PREFERENCE_EMAIL_INTERVAL_FIFTEEN ||
 		emailInterval == PREFERENCE_EMAIL_INTERVAL_HOUR
 }
+
+func IsValidLocale(locale string) bool {
+	if locale != "" {
+		if len(locale) > USER_LOCALE_MAX_LENGTH {
+			return false
+		} else if _, err := language.Parse(locale); err != nil {
+			return false
+		}
+	}
+
+	return true
+}
diff --git a/model/user_test.go b/model/user_test.go
index d7f7b67114..bdd8f20038 100644
--- a/model/user_test.go
+++ b/model/user_test.go
@@ -332,3 +332,59 @@ func TestRoles(t *testing.T) {
 	require.True(t, IsInRole("system_admin junk", "system_admin"))
 	require.False(t, IsInRole("admin", "system_admin"))
 }
+
+func TestIsValidLocale(t *testing.T) {
+	for _, test := range []struct {
+		Name     string
+		Locale   string
+		Expected bool
+	}{
+		{
+			Name:     "empty locale",
+			Locale:   "",
+			Expected: true,
+		},
+		{
+			Name:     "locale with only language",
+			Locale:   "fr",
+			Expected: true,
+		},
+		{
+			Name:     "locale with region",
+			Locale:   "en-DE", // English, as used in Germany
+			Expected: true,
+		},
+		{
+			Name:     "invalid locale",
+			Locale:   "'",
+			Expected: false,
+		},
+
+		// Note that the following cases are all valid language tags, but they're considered invalid here because of
+		// the max length of the User.Locale field.
+		{
+			Name:     "locale with extended language subtag",
+			Locale:   "zh-yue-HK", // Chinese, Cantonese, as used in Hong Kong
+			Expected: false,
+		},
+		{
+			Name:     "locale with script",
+			Locale:   "hy-Latn-IT-arevela", // Eastern Armenian written in Latin script, as used in Italy
+			Expected: false,
+		},
+		{
+			Name:     "locale with variant",
+			Locale:   "sl-rozaj-biske", // San Giorgio dialect of Resian dialect of Slovenian
+			Expected: false,
+		},
+		{
+			Name:     "locale with extension",
+			Locale:   "de-DE-u-co-phonebk", // German, as used in Germany, using German phonebook sort order
+			Expected: false,
+		},
+	} {
+		t.Run(test.Name, func(t *testing.T) {
+			assert.Equal(t, test.Expected, IsValidLocale(test.Locale))
+		})
+	}
+}