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gui_csrf.go
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gui_csrf.go
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// Copyright (C) 2014 The Syncthing Authors.
//
// This program is free software: you can redistribute it and/or modify it
// under the terms of the GNU General Public License as published by the Free
// Software Foundation, either version 3 of the License, or (at your option)
// any later version.
//
// This program is distributed in the hope that it will be useful, but WITHOUT
// ANY WARRANTY; without even the implied warranty of MERCHANTABILITY or
// FITNESS FOR A PARTICULAR PURPOSE. See the GNU General Public License for
// more details.
//
// You should have received a copy of the GNU General Public License along
// with this program. If not, see <http://www.gnu.org/licenses/>.
package main
import (
"bufio"
"fmt"
"net/http"
"os"
"path/filepath"
"strings"
"sync"
"time"
"github.com/syncthing/syncthing/internal/osutil"
)
var csrfTokens []string
var csrfMut sync.Mutex
// Check for CSRF token on /rest/ URLs. If a correct one is not given, reject
// the request with 403. For / and /index.html, set a new CSRF cookie if none
// is currently set.
func csrfMiddleware(prefix, apiKey string, next http.Handler) http.Handler {
loadCsrfTokens()
return http.HandlerFunc(func(w http.ResponseWriter, r *http.Request) {
// Allow requests carrying a valid API key
if apiKey != "" && r.Header.Get("X-API-Key") == apiKey {
next.ServeHTTP(w, r)
return
}
// Allow requests for the front page, and set a CSRF cookie if there isn't already a valid one.
if !strings.HasPrefix(r.URL.Path, prefix) {
cookie, err := r.Cookie("CSRF-Token")
if err != nil || !validCsrfToken(cookie.Value) {
cookie = &http.Cookie{
Name: "CSRF-Token",
Value: newCsrfToken(),
}
http.SetCookie(w, cookie)
}
next.ServeHTTP(w, r)
return
}
if r.Method == "GET" {
// Allow GET requests unconditionally
next.ServeHTTP(w, r)
return
}
// Verify the CSRF token
token := r.Header.Get("X-CSRF-Token")
if !validCsrfToken(token) {
http.Error(w, "CSRF Error", 403)
return
}
next.ServeHTTP(w, r)
})
}
func validCsrfToken(token string) bool {
csrfMut.Lock()
defer csrfMut.Unlock()
for _, t := range csrfTokens {
if t == token {
return true
}
}
return false
}
func newCsrfToken() string {
token := randomString(32)
csrfMut.Lock()
csrfTokens = append(csrfTokens, token)
if len(csrfTokens) > 10 {
csrfTokens = csrfTokens[len(csrfTokens)-10:]
}
defer csrfMut.Unlock()
saveCsrfTokens()
return token
}
func saveCsrfTokens() {
name := filepath.Join(confDir, "csrftokens.txt")
tmp := fmt.Sprintf("%s.tmp.%d", name, time.Now().UnixNano())
f, err := os.OpenFile(tmp, os.O_CREATE|os.O_EXCL|os.O_WRONLY, 0644)
if err != nil {
return
}
defer os.Remove(tmp)
for _, t := range csrfTokens {
_, err := fmt.Fprintln(f, t)
if err != nil {
return
}
}
err = f.Close()
if err != nil {
return
}
osutil.Rename(tmp, name)
}
func loadCsrfTokens() {
name := filepath.Join(confDir, "csrftokens.txt")
f, err := os.Open(name)
if err != nil {
return
}
defer f.Close()
s := bufio.NewScanner(f)
for s.Scan() {
csrfTokens = append(csrfTokens, s.Text())
}
}