144 lines
3.6 KiB
Go
144 lines
3.6 KiB
Go
// Copyright (C) 2014 The Syncthing Authors.
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//
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// This Source Code Form is subject to the terms of the Mozilla Public
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// License, v. 2.0. If a copy of the MPL was not distributed with this file,
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// You can obtain one at http://mozilla.org/MPL/2.0/.
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package main
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import (
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"bufio"
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"fmt"
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"net/http"
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"os"
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"strings"
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"github.com/syncthing/syncthing/lib/config"
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"github.com/syncthing/syncthing/lib/osutil"
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"github.com/syncthing/syncthing/lib/sync"
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"github.com/syncthing/syncthing/lib/util"
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)
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// csrfTokens is a list of valid tokens. It is sorted so that the most
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// recently used token is first in the list. New tokens are added to the front
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// of the list (as it is the most recently used at that time). The list is
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// pruned to a maximum of maxCsrfTokens, throwing away the least recently used
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// tokens.
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var csrfTokens []string
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var csrfMut = sync.NewMutex()
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const maxCsrfTokens = 25
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// Check for CSRF token on /rest/ URLs. If a correct one is not given, reject
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// the request with 403. For / and /index.html, set a new CSRF cookie if none
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// is currently set.
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func csrfMiddleware(unique string, prefix string, cfg config.GUIConfiguration, next http.Handler) http.Handler {
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loadCsrfTokens()
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return http.HandlerFunc(func(w http.ResponseWriter, r *http.Request) {
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// Allow requests carrying a valid API key
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if cfg.IsValidAPIKey(r.Header.Get("X-API-Key")) {
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next.ServeHTTP(w, r)
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return
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}
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// Allow requests for the front page, and set a CSRF cookie if there isn't already a valid one.
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if !strings.HasPrefix(r.URL.Path, prefix) {
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cookie, err := r.Cookie("CSRF-Token-" + unique)
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if err != nil || !validCsrfToken(cookie.Value) {
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httpl.Debugln("new CSRF cookie in response to request for", r.URL)
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cookie = &http.Cookie{
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Name: "CSRF-Token-" + unique,
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Value: newCsrfToken(),
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}
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http.SetCookie(w, cookie)
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}
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next.ServeHTTP(w, r)
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return
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}
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if r.Method == "GET" {
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// Allow GET requests unconditionally, but if we got the CSRF
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// token cookie do the verification anyway so we keep the
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// csrfTokens list sorted by recent usage. We don't care about the
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// outcome of the validity check.
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if cookie, err := r.Cookie("CSRF-Token-" + unique); err == nil {
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validCsrfToken(cookie.Value)
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}
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next.ServeHTTP(w, r)
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return
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}
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// Verify the CSRF token
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token := r.Header.Get("X-CSRF-Token-" + unique)
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if !validCsrfToken(token) {
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http.Error(w, "CSRF Error", 403)
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return
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}
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next.ServeHTTP(w, r)
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})
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}
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func validCsrfToken(token string) bool {
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csrfMut.Lock()
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defer csrfMut.Unlock()
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for i, t := range csrfTokens {
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if t == token {
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if i > 0 {
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// Move this token to the head of the list. Copy the tokens at
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// the front one step to the right and then replace the token
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// at the head.
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copy(csrfTokens[1:], csrfTokens[:i+1])
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csrfTokens[0] = token
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}
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return true
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}
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}
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return false
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}
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func newCsrfToken() string {
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token := util.RandomString(32)
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csrfMut.Lock()
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csrfTokens = append([]string{token}, csrfTokens...)
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if len(csrfTokens) > maxCsrfTokens {
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csrfTokens = csrfTokens[:maxCsrfTokens]
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}
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defer csrfMut.Unlock()
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saveCsrfTokens()
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return token
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}
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func saveCsrfTokens() {
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// We're ignoring errors in here. It's not super critical and there's
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// nothing relevant we can do about them anyway...
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name := locations[locCsrfTokens]
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f, err := osutil.CreateAtomic(name, 0600)
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if err != nil {
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return
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}
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for _, t := range csrfTokens {
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fmt.Fprintln(f, t)
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}
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f.Close()
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}
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func loadCsrfTokens() {
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f, err := os.Open(locations[locCsrfTokens])
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if err != nil {
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return
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}
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defer f.Close()
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s := bufio.NewScanner(f)
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for s.Scan() {
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csrfTokens = append(csrfTokens, s.Text())
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}
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}
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