From d06f9ce27452ec0b80d548242bf59d65f89952bf Mon Sep 17 00:00:00 2001
From: zeripath <art27@cantab.net>
Date: Thu, 8 Jul 2021 14:57:24 +0100
Subject: [PATCH] Redirect on bad CSRF instead of presenting bad page (#14937)

The current CSRF handler is a bit harsh with bad CSRF tokens on webpages
I think we can be a little kinder and redirect to base page with a flash error

Signed-off-by: Andrew Thornton <art27@cantab.net>
---
 integrations/repo_branch_test.go | 11 ++++++++++-
 modules/context/csrf.go          | 23 +++++++++++++++++++----
 options/locale/locale_en-US.ini  |  2 ++
 3 files changed, 31 insertions(+), 5 deletions(-)

diff --git a/integrations/repo_branch_test.go b/integrations/repo_branch_test.go
index de4e66898797..af5c475ea7dc 100644
--- a/integrations/repo_branch_test.go
+++ b/integrations/repo_branch_test.go
@@ -11,6 +11,7 @@ import (
 	"strings"
 	"testing"
 
+	"code.gitea.io/gitea/modules/setting"
 	"code.gitea.io/gitea/modules/test"
 
 	"github.com/stretchr/testify/assert"
@@ -134,5 +135,13 @@ func TestCreateBranchInvalidCSRF(t *testing.T) {
 		"_csrf":           "fake_csrf",
 		"new_branch_name": "test",
 	})
-	session.MakeRequest(t, req, http.StatusBadRequest)
+	resp := session.MakeRequest(t, req, http.StatusFound)
+	loc := resp.Header().Get("Location")
+	assert.Equal(t, setting.AppSubURL+"/", loc)
+	resp = session.MakeRequest(t, NewRequest(t, "GET", loc), http.StatusOK)
+	htmlDoc := NewHTMLParser(t, resp.Body)
+	assert.Equal(t,
+		"Bad Request: Invalid CSRF token",
+		strings.TrimSpace(htmlDoc.doc.Find(".ui.message").Text()),
+	)
 }
diff --git a/modules/context/csrf.go b/modules/context/csrf.go
index ba0e9f6cde77..8d179ca90474 100644
--- a/modules/context/csrf.go
+++ b/modules/context/csrf.go
@@ -22,6 +22,7 @@ import (
 	"net/http"
 	"time"
 
+	"code.gitea.io/gitea/modules/setting"
 	"code.gitea.io/gitea/modules/web/middleware"
 
 	"github.com/unknwon/com"
@@ -266,7 +267,12 @@ func Validate(ctx *Context, x CSRF) {
 				-1,
 				x.GetCookiePath(),
 				x.GetCookieDomain()) // FIXME: Do we need to set the Secure, httpOnly and SameSite values too?
-			x.Error(ctx.Resp)
+			if middleware.IsAPIPath(ctx.Req) {
+				x.Error(ctx.Resp)
+				return
+			}
+			ctx.Flash.Error(ctx.Tr("error.invalid_csrf"))
+			ctx.Redirect(setting.AppSubURL + "/")
 		}
 		return
 	}
@@ -277,10 +283,19 @@ func Validate(ctx *Context, x CSRF) {
 				-1,
 				x.GetCookiePath(),
 				x.GetCookieDomain()) // FIXME: Do we need to set the Secure, httpOnly and SameSite values too?
-			x.Error(ctx.Resp)
+			if middleware.IsAPIPath(ctx.Req) {
+				x.Error(ctx.Resp)
+				return
+			}
+			ctx.Flash.Error(ctx.Tr("error.invalid_csrf"))
+			ctx.Redirect(setting.AppSubURL + "/")
 		}
 		return
 	}
-
-	http.Error(ctx.Resp, "Bad Request: no CSRF token present", http.StatusBadRequest)
+	if middleware.IsAPIPath(ctx.Req) {
+		http.Error(ctx.Resp, "Bad Request: no CSRF token present", http.StatusBadRequest)
+		return
+	}
+	ctx.Flash.Error(ctx.Tr("error.missing_csrf"))
+	ctx.Redirect(setting.AppSubURL + "/")
 }
diff --git a/options/locale/locale_en-US.ini b/options/locale/locale_en-US.ini
index dcdfa611ec95..7f58a11e7385 100644
--- a/options/locale/locale_en-US.ini
+++ b/options/locale/locale_en-US.ini
@@ -100,6 +100,8 @@ never = Never
 [error]
 occurred = An error has occurred
 report_message = If you are sure this is a Gitea bug, please search for issue on <a href="https://github.com/go-gitea/gitea/issues">GitHub</a> and open new issue if necessary.
+missing_csrf = Bad Request: no CSRF token present
+invalid_csrf = Bad Request: Invalid CSRF token
 
 [startpage]
 app_desc = A painless, self-hosted Git service