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// Copyright (C) 2014 The Syncthing Authors.
//
// This Source Code Form is subject to the terms of the Mozilla Public
// License, v. 2.0. If a copy of the MPL was not distributed with this file,
// You can obtain one at https://mozilla.org/MPL/2.0/.
package api
import (
"bufio"
"fmt"
"net/http"
"os"
"strings"
"github.com/syncthing/syncthing/lib/osutil"
"github.com/syncthing/syncthing/lib/rand"
"github.com/syncthing/syncthing/lib/sync"
)
const maxCsrfTokens = 25
type csrfManager struct {
// tokens is a list of valid tokens. It is sorted so that the most
// recently used token is first in the list. New tokens are added to the front
// of the list (as it is the most recently used at that time). The list is
// pruned to a maximum of maxCsrfTokens, throwing away the least recently used
// tokens.
tokens []string
tokensMut sync.Mutex
unique string
prefix string
apiKeyValidator apiKeyValidator
next http.Handler
saveLocation string
}
type apiKeyValidator interface {
IsValidAPIKey(key string) bool
}
// 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 newCsrfManager(unique string, prefix string, apiKeyValidator apiKeyValidator, next http.Handler, saveLocation string) *csrfManager {
m := &csrfManager{
tokensMut: sync.NewMutex(),
tokens: make([]string, 0, maxCsrfTokens),
unique: unique,
prefix: prefix,
apiKeyValidator: apiKeyValidator,
next: next,
saveLocation: saveLocation,
}
m.load()
return m
}
func (m *csrfManager) ServeHTTP(w http.ResponseWriter, r *http.Request) {
// Allow requests carrying a valid API key
if hasValidAPIKeyHeader(r, m.apiKeyValidator) {
// Set the access-control-allow-origin header for CORS requests
// since a valid API key has been provided
w.Header().Add("Access-Control-Allow-Origin", "*")
m.next.ServeHTTP(w, r)
return
}
if strings.HasPrefix(r.URL.Path, "/rest/debug") {
// Debugging functions are only available when explicitly
// enabled, and can be accessed without a CSRF token
m.next.ServeHTTP(w, r)
return
}
// Allow requests for anything not under the protected path prefix,
// and set a CSRF cookie if there isn't already a valid one.
if !strings.HasPrefix(r.URL.Path, m.prefix) {
cookie, err := r.Cookie("CSRF-Token-" + m.unique)
if err != nil || !m.validToken(cookie.Value) {
l.Debugln("new CSRF cookie in response to request for", r.URL)
cookie = &http.Cookie{
Name: "CSRF-Token-" + m.unique,
Value: m.newToken(),
}
http.SetCookie(w, cookie)
}
m.next.ServeHTTP(w, r)
return
}
if isNoAuthPath(r.URL.Path) {
// REST calls that don't require authentication also do not
// need a CSRF token.
m.next.ServeHTTP(w, r)
return
}
// Verify the CSRF token
token := r.Header.Get("X-CSRF-Token-" + m.unique)
if !m.validToken(token) {
http.Error(w, "CSRF Error", http.StatusForbidden)
return
}
m.next.ServeHTTP(w, r)
}
func (m *csrfManager) validToken(token string) bool {
m.tokensMut.Lock()
defer m.tokensMut.Unlock()
for i, t := range m.tokens {
if t == token {
if i > 0 {
// Move this token to the head of the list. Copy the tokens at
// the front one step to the right and then replace the token
// at the head.
copy(m.tokens[1:], m.tokens[:i])
m.tokens[0] = token
}
return true
}
}
return false
}
func (m *csrfManager) newToken() string {
token := rand.String(32)
m.tokensMut.Lock()
defer m.tokensMut.Unlock()
if len(m.tokens) < maxCsrfTokens {
m.tokens = append(m.tokens, "")
}
copy(m.tokens[1:], m.tokens)
m.tokens[0] = token
m.save()
return token
}
func (m *csrfManager) save() {
// We're ignoring errors in here. It's not super critical and there's
// nothing relevant we can do about them anyway...
if m.saveLocation == "" {
return
}
f, err := osutil.CreateAtomic(m.saveLocation)
if err != nil {
return
}
for _, t := range m.tokens {
fmt.Fprintln(f, t)
}
f.Close()
}
func (m *csrfManager) load() {
if m.saveLocation == "" {
return
}
f, err := os.Open(m.saveLocation)
if err != nil {
return
}
defer f.Close()
s := bufio.NewScanner(f)
for s.Scan() {
m.tokens = append(m.tokens, s.Text())
}
}
func hasValidAPIKeyHeader(r *http.Request, validator apiKeyValidator) bool {
if key := r.Header.Get("X-API-Key"); validator.IsValidAPIKey(key) {
return true
}
if auth := r.Header.Get("Authorization"); strings.HasPrefix(strings.ToLower(auth), "bearer ") {
bearerToken := auth[len("bearer "):]
return validator.IsValidAPIKey(bearerToken)
}
return false
}
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