Improve valid user name check (#20136)

Close https://github.com/go-gitea/gitea/issues/21640

Before: Gitea can create users like ".xxx" or "x..y", which is not
ideal, it's already a consensus that dot filenames have special
meanings, and `a..b` is a confusing name when doing cross repo compare.

After: stricter

Co-authored-by: Jason Song <i@wolfogre.com>
Co-authored-by: Lunny Xiao <xiaolunwen@gmail.com>
Co-authored-by: delvh <dev.lh@web.de>

12 files changed, 95 insertions, 14 deletions

diff --git a/models/user/user.go b/models/user/user.go
index 9a2da6dbc1..84e2c4a9cc 100644
--- a/models/user/user.go
+++ b/models/user/user.go
@@ -29,6 +29,7 @@ import (
 	"code.gitea.io/gitea/modules/structs"
 	"code.gitea.io/gitea/modules/timeutil"
 	"code.gitea.io/gitea/modules/util"
+	"code.gitea.io/gitea/modules/validation"
 
 	"golang.org/x/crypto/argon2"
 	"golang.org/x/crypto/bcrypt"
@@ -621,7 +622,7 @@ var (
 // IsUsableUsername returns an error when a username is reserved
 func IsUsableUsername(name string) error {
 	// Validate username make sure it satisfies requirement.
-	if db.AlphaDashDotPattern.MatchString(name) {
+	if !validation.IsValidUsername(name) {
 		// Note: usually this error is normally caught up earlier in the UI
 		return db.ErrNameCharsNotAllowed{Name: name}
 	}
diff --git a/modules/structs/admin_user.go b/modules/structs/admin_user.go
index eccbf29a46..2f6f502af6 100644
--- a/modules/structs/admin_user.go
+++ b/modules/structs/admin_user.go
@@ -10,7 +10,7 @@ type CreateUserOption struct {
 	SourceID  int64  `json:"source_id"`
 	LoginName string `json:"login_name"`
 	// required: true
-	Username string `json:"username" binding:"Required;AlphaDashDot;MaxSize(40)"`
+	Username string `json:"username" binding:"Required;Username;MaxSize(40)"`
 	FullName string `json:"full_name" binding:"MaxSize(100)"`
 	// required: true
 	// swagger:strfmt email
diff --git a/modules/validation/binding.go b/modules/validation/binding.go
index f08f632426..c054fbe7b6 100644
--- a/modules/validation/binding.go
+++ b/modules/validation/binding.go
@@ -24,6 +24,9 @@ const (
 
 	// ErrRegexPattern is returned when a regex pattern is invalid
 	ErrRegexPattern = "RegexPattern"
+
+	// ErrUsername is username error
+	ErrUsername = "UsernameError"
 )
 
 // AddBindingRules adds additional binding rules
@@ -34,6 +37,7 @@ func AddBindingRules() {
 	addGlobPatternRule()
 	addRegexPatternRule()
 	addGlobOrRegexPatternRule()
+	addUsernamePatternRule()
 }
 
 func addGitRefNameBindingRule() {
@@ -148,6 +152,22 @@ func addGlobOrRegexPatternRule() {
 	})
 }
 
+func addUsernamePatternRule() {
+	binding.AddRule(&binding.Rule{
+		IsMatch: func(rule string) bool {
+			return rule == "Username"
+		},
+		IsValid: func(errs binding.Errors, name string, val interface{}) (bool, binding.Errors) {
+			str := fmt.Sprintf("%v", val)
+			if !IsValidUsername(str) {
+				errs.Add([]string{name}, ErrUsername, "invalid username")
+				return false, errs
+			}
+			return true, errs
+		},
+	})
+}
+
 func portOnly(hostport string) string {
 	colon := strings.IndexByte(hostport, ':')
 	if colon == -1 {
diff --git a/modules/validation/helpers.go b/modules/validation/helpers.go
index 484b12b2a2..8e49c7855e 100644
--- a/modules/validation/helpers.go
+++ b/modules/validation/helpers.go
@@ -91,3 +91,15 @@ func IsValidExternalTrackerURLFormat(uri string) bool {
 
 	return true
 }
+
+var (
+	validUsernamePattern   = regexp.MustCompile(`^[\da-zA-Z][-.\w]*$`)
+	invalidUsernamePattern = regexp.MustCompile(`[-._]{2,}|[-._]$`) // No consecutive or trailing non-alphanumeric chars
+)
+
+// IsValidUsername checks if username is valid
+func IsValidUsername(name string) bool {
+	// It is difficult to find a single pattern that is both readable and effective,
+	// but it's easier to use positive and negative checks.
+	return validUsernamePattern.MatchString(name) && !invalidUsernamePattern.MatchString(name)
+}
diff --git a/modules/validation/helpers_test.go b/modules/validation/helpers_test.go
index f6f897e821..9bdbdb4a77 100644
--- a/modules/validation/helpers_test.go
+++ b/modules/validation/helpers_test.go
@@ -155,3 +155,34 @@ func Test_IsValidExternalTrackerURLFormat(t *testing.T) {
 		})
 	}
 }
+
+func TestIsValidUsername(t *testing.T) {
+	tests := []struct {
+		arg  string
+		want bool
+	}{
+		{arg: "a", want: true},
+		{arg: "abc", want: true},
+		{arg: "0.b-c", want: true},
+		{arg: "a.b-c_d", want: true},
+		{arg: "", want: false},
+		{arg: ".abc", want: false},
+		{arg: "abc.", want: false},
+		{arg: "a..bc", want: false},
+		{arg: "a...bc", want: false},
+		{arg: "a.-bc", want: false},
+		{arg: "a._bc", want: false},
+		{arg: "a_-bc", want: false},
+		{arg: "a/bc", want: false},
+		{arg: "☁️", want: false},
+		{arg: "-", want: false},
+		{arg: "--diff", want: false},
+		{arg: "-im-here", want: false},
+		{arg: "a space", want: false},
+	}
+	for _, tt := range tests {
+		t.Run(tt.arg, func(t *testing.T) {
+			assert.Equalf(t, tt.want, IsValidUsername(tt.arg), "IsValidUsername(%v)", tt.arg)
+		})
+	}
+}
diff --git a/modules/web/middleware/binding.go b/modules/web/middleware/binding.go
index 636e655b9e..cced9717be 100644
--- a/modules/web/middleware/binding.go
+++ b/modules/web/middleware/binding.go
@@ -135,6 +135,8 @@ func Validate(errs binding.Errors, data map[string]interface{}, f Form, l transl
 				data["ErrorMsg"] = trName + l.Tr("form.glob_pattern_error", errs[0].Message)
 			case validation.ErrRegexPattern:
 				data["ErrorMsg"] = trName + l.Tr("form.regex_pattern_error", errs[0].Message)
+			case validation.ErrUsername:
+				data["ErrorMsg"] = trName + l.Tr("form.username_error")
 			default:
 				msg := errs[0].Classification
 				if msg != "" && errs[0].Message != "" {
diff --git a/options/locale/locale_en-US.ini b/options/locale/locale_en-US.ini
index 8cda250559..32da24b6b0 100644
--- a/options/locale/locale_en-US.ini
+++ b/options/locale/locale_en-US.ini
@@ -463,6 +463,7 @@ url_error = `'%s' is not a valid URL.`
 include_error = ` must contain substring '%s'.`
 glob_pattern_error = ` glob pattern is invalid: %s.`
 regex_pattern_error = ` regex pattern is invalid: %s.`
+username_error = ` can only contain alphanumeric chars ('0-9','a-z','A-Z'), dash ('-'), underscore ('_') and dot ('.'). It cannot begin or end with non-alphanumeric chars, and consecutive non-alphanumeric chars are also forbidden.`
 unknown_error = Unknown error:
 captcha_incorrect = The CAPTCHA code is incorrect.
 password_not_match = The passwords do not match.
diff --git a/services/forms/admin.go b/services/forms/admin.go
index 5abef0550e..537b9f982c 100644
--- a/services/forms/admin.go
+++ b/services/forms/admin.go
@@ -18,7 +18,7 @@ import (
 type AdminCreateUserForm struct {
 	LoginType          string `binding:"Required"`
 	LoginName          string
-	UserName           string `binding:"Required;AlphaDashDot;MaxSize(40)"`
+	UserName           string `binding:"Required;Username;MaxSize(40)"`
 	Email              string `binding:"Required;Email;MaxSize(254)"`
 	Password           string `binding:"MaxSize(255)"`
 	SendNotify         bool
@@ -35,7 +35,7 @@ func (f *AdminCreateUserForm) Validate(req *http.Request, errs binding.Errors) b
 // AdminEditUserForm form for admin to create user
 type AdminEditUserForm struct {
 	LoginType               string `binding:"Required"`
-	UserName                string `binding:"AlphaDashDot;MaxSize(40)"`
+	UserName                string `binding:"Username;MaxSize(40)"`
 	LoginName               string
 	FullName                string `binding:"MaxSize(100)"`
 	Email                   string `binding:"Required;Email;MaxSize(254)"`
diff --git a/services/forms/org.go b/services/forms/org.go
index dec2dbfa65..c7ee911345 100644
--- a/services/forms/org.go
+++ b/services/forms/org.go
@@ -24,7 +24,7 @@ import (
 
 // CreateOrgForm form for creating organization
 type CreateOrgForm struct {
-	OrgName                   string `binding:"Required;AlphaDashDot;MaxSize(40)" locale:"org.org_name_holder"`
+	OrgName                   string `binding:"Required;Username;MaxSize(40)" locale:"org.org_name_holder"`
 	Visibility                structs.VisibleType
 	RepoAdminChangeTeamAccess bool
 }
@@ -37,7 +37,7 @@ func (f *CreateOrgForm) Validate(req *http.Request, errs binding.Errors) binding
 
 // UpdateOrgSettingForm form for updating organization settings
 type UpdateOrgSettingForm struct {
-	Name                      string `binding:"Required;AlphaDashDot;MaxSize(40)" locale:"org.org_name_holder"`
+	Name                      string `binding:"Required;Username;MaxSize(40)" locale:"org.org_name_holder"`
 	FullName                  string `binding:"MaxSize(100)"`
 	Description               string `binding:"MaxSize(255)"`
 	Website                   string `binding:"ValidUrl;MaxSize(255)"`
diff --git a/services/forms/user_form.go b/services/forms/user_form.go
index 95e4f9ed0e..ed8ccf12ea 100644
--- a/services/forms/user_form.go
+++ b/services/forms/user_form.go
@@ -65,7 +65,7 @@ type InstallForm struct {
 
 	PasswordAlgorithm string
 
-	AdminName          string `binding:"OmitEmpty;AlphaDashDot;MaxSize(30)" locale:"install.admin_name"`
+	AdminName          string `binding:"OmitEmpty;Username;MaxSize(30)" locale:"install.admin_name"`
 	AdminPasswd        string `binding:"OmitEmpty;MaxSize(255)" locale:"install.admin_password"`
 	AdminConfirmPasswd string
 	AdminEmail         string `binding:"OmitEmpty;MinSize(3);MaxSize(254);Include(@)" locale:"install.admin_email"`
@@ -91,7 +91,7 @@ func (f *InstallForm) Validate(req *http.Request, errs binding.Errors) binding.E
 
 // RegisterForm form for registering
 type RegisterForm struct {
-	UserName           string `binding:"Required;AlphaDashDot;MaxSize(40)"`
+	UserName           string `binding:"Required;Username;MaxSize(40)"`
 	Email              string `binding:"Required;MaxSize(254)"`
 	Password           string `binding:"MaxSize(255)"`
 	Retype             string
@@ -243,7 +243,7 @@ func (f *IntrospectTokenForm) Validate(req *http.Request, errs binding.Errors) b
 
 // UpdateProfileForm form for updating profile
 type UpdateProfileForm struct {
-	Name                string `binding:"AlphaDashDot;MaxSize(40)"`
+	Name                string `binding:"Username;MaxSize(40)"`
 	FullName            string `binding:"MaxSize(100)"`
 	KeepEmailPrivate    bool
 	Website             string `binding:"ValidSiteUrl;MaxSize(255)"`
diff --git a/services/forms/user_form_auth_openid.go b/services/forms/user_form_auth_openid.go
index 992517f34f..d1ed0a23c7 100644
--- a/services/forms/user_form_auth_openid.go
+++ b/services/forms/user_form_auth_openid.go
@@ -27,7 +27,7 @@ func (f *SignInOpenIDForm) Validate(req *http.Request, errs binding.Errors) bind
 
 // SignUpOpenIDForm form for signin up with OpenID
 type SignUpOpenIDForm struct {
-	UserName           string `binding:"Required;AlphaDashDot;MaxSize(40)"`
+	UserName           string `binding:"Required;Username;MaxSize(40)"`
 	Email              string `binding:"Required;Email;MaxSize(254)"`
 	GRecaptchaResponse string `form:"g-recaptcha-response"`
 	HcaptchaResponse   string `form:"h-captcha-response"`
diff --git a/tests/integration/user_test.go b/tests/integration/user_test.go
index 110f5c89bf..017700ad40 100644
--- a/tests/integration/user_test.go
+++ b/tests/integration/user_test.go
@@ -53,6 +53,22 @@ func TestRenameInvalidUsername(t *testing.T) {
 		"%00",
 		"thisHas ASpace",
 		"p<A>tho>lo<gical",
+		".",
+		"..",
+		".well-known",
+		".abc",
+		"abc.",
+		"a..bc",
+		"a...bc",
+		"a.-bc",
+		"a._bc",
+		"a_-bc",
+		"a/bc",
+		"☁️",
+		"-",
+		"--diff",
+		"-im-here",
+		"a space",
 	}
 
 	session := loginUser(t, "user2")
@@ -68,7 +84,7 @@ func TestRenameInvalidUsername(t *testing.T) {
 		htmlDoc := NewHTMLParser(t, resp.Body)
 		assert.Contains(t,
 			htmlDoc.doc.Find(".ui.negative.message").Text(),
-			translation.NewLocale("en-US").Tr("form.alpha_dash_dot_error"),
+			translation.NewLocale("en-US").Tr("form.username_error"),
 		)
 
 		unittest.AssertNotExistsBean(t, &user_model.User{Name: invalidUsername})
@@ -79,9 +95,7 @@ func TestRenameReservedUsername(t *testing.T) {
 	defer tests.PrepareTestEnv(t)()
 
 	reservedUsernames := []string{
-		".",
-		"..",
-		".well-known",
+		// ".", "..", ".well-known", // The names are not only reserved but also invalid
 		"admin",
 		"api",
 		"assets",