Quelle  cookie.c   Sprache: C

// SPDX-License-Identifier: GPL-2.0
/*
 * Copyright (C) 2015-2019 Jason A. Donenfeld <Jason@zx2c4.com>. All Rights Reserved.
 */

#include "cookie.h"
#include "peer.h"
#include "device.h"
#include "messages.h"
#include "ratelimiter.h"
#include "timers.h"

#include <crypto/blake2s.h>
#include <crypto/chacha20poly1305.h>
#include <crypto/utils.h>

#include <net/ipv6.h>

void wg_cookie_checker_init(struct cookie_checker *checker,
       struct wg_device *wg)
{
 init_rwsem(&checker->secret_lock);
 checker->secret_birthdate = ktime_get_coarse_boottime_ns();
 get_random_bytes(checker->secret, NOISE_HASH_LEN);
 checker->device = wg;
}

enum { COOKIE_KEY_LABEL_LEN = 8 };
static const u8 mac1_key_label[COOKIE_KEY_LABEL_LEN] __nonstring = "mac1----";
static const u8 cookie_key_label[COOKIE_KEY_LABEL_LEN] __nonstring = "cookie--";

static void precompute_key(u8 key[NOISE_SYMMETRIC_KEY_LEN],
      const u8 pubkey[NOISE_PUBLIC_KEY_LEN],
      const u8 label[COOKIE_KEY_LABEL_LEN])
{
 struct blake2s_state blake;

 blake2s_init(&blake, NOISE_SYMMETRIC_KEY_LEN);
 blake2s_update(&blake, label, COOKIE_KEY_LABEL_LEN);
 blake2s_update(&blake, pubkey, NOISE_PUBLIC_KEY_LEN);
 blake2s_final(&blake, key);
}

/* Must hold peer->handshake.static_identity->lock */
void wg_cookie_checker_precompute_device_keys(struct cookie_checker *checker)
{
 if (likely(checker->device->static_identity.has_identity)) {
  precompute_key(checker->cookie_encryption_key,
          checker->device->static_identity.static_public,
          cookie_key_label);
  precompute_key(checker->message_mac1_key,
          checker->device->static_identity.static_public,
          mac1_key_label);
 } else {
  memset(checker->cookie_encryption_key, 0,
         NOISE_SYMMETRIC_KEY_LEN);
  memset(checker->message_mac1_key, 0, NOISE_SYMMETRIC_KEY_LEN);
 }
}

void wg_cookie_checker_precompute_peer_keys(struct wg_peer *peer)
{
 precompute_key(peer->latest_cookie.cookie_decryption_key,
         peer->handshake.remote_static, cookie_key_label);
 precompute_key(peer->latest_cookie.message_mac1_key,
         peer->handshake.remote_static, mac1_key_label);
}

void wg_cookie_init(struct cookie *cookie)
{
 memset(cookie, 0, sizeof(*cookie));
 init_rwsem(&cookie->lock);
}

static void compute_mac1(u8 mac1[COOKIE_LEN], const void *message, size_t len,
    const u8 key[NOISE_SYMMETRIC_KEY_LEN])
{
 len = len - sizeof(struct message_macs) +
       offsetof(struct message_macs, mac1);
 blake2s(mac1, message, key, COOKIE_LEN, len, NOISE_SYMMETRIC_KEY_LEN);
}

static void compute_mac2(u8 mac2[COOKIE_LEN], const void *message, size_t len,
    const u8 cookie[COOKIE_LEN])
{
 len = len - sizeof(struct message_macs) +
       offsetof(struct message_macs, mac2);
 blake2s(mac2, message, cookie, COOKIE_LEN, len, COOKIE_LEN);
}

static void make_cookie(u8 cookie[COOKIE_LEN], struct sk_buff *skb,
   struct cookie_checker *checker)
{
 struct blake2s_state state;

 if (wg_birthdate_has_expired(checker->secret_birthdate,
         COOKIE_SECRET_MAX_AGE)) {
  down_write(&checker->secret_lock);
  checker->secret_birthdate = ktime_get_coarse_boottime_ns();
  get_random_bytes(checker->secret, NOISE_HASH_LEN);
  up_write(&checker->secret_lock);
 }

 down_read(&checker->secret_lock);

 blake2s_init_key(&state, COOKIE_LEN, checker->secret, NOISE_HASH_LEN);
 if (skb->protocol == htons(ETH_P_IP))
  blake2s_update(&state, (u8 *)&ip_hdr(skb)->saddr,
          sizeof(struct in_addr));
 else if (skb->protocol == htons(ETH_P_IPV6))
  blake2s_update(&state, (u8 *)&ipv6_hdr(skb)->saddr,
          sizeof(struct in6_addr));
 blake2s_update(&state, (u8 *)&udp_hdr(skb)->source, sizeof(__be16));
 blake2s_final(&state, cookie);

 up_read(&checker->secret_lock);
}

enum cookie_mac_state wg_cookie_validate_packet(struct cookie_checker *checker,
      struct sk_buff *skb,
      bool check_cookie)
{
 struct message_macs *macs = (struct message_macs *)
  (skb->data + skb->len - sizeof(*macs));
 enum cookie_mac_state ret;
 u8 computed_mac[COOKIE_LEN];
 u8 cookie[COOKIE_LEN];

 ret = INVALID_MAC;
 compute_mac1(computed_mac, skb->data, skb->len,
       checker->message_mac1_key);
 if (crypto_memneq(computed_mac, macs->mac1, COOKIE_LEN))
  goto out;

 ret = VALID_MAC_BUT_NO_COOKIE;

 if (!check_cookie)
  goto out;

 make_cookie(cookie, skb, checker);

 compute_mac2(computed_mac, skb->data, skb->len, cookie);
 if (crypto_memneq(computed_mac, macs->mac2, COOKIE_LEN))
  goto out;

 ret = VALID_MAC_WITH_COOKIE_BUT_RATELIMITED;
 if (!wg_ratelimiter_allow(skb, dev_net(checker->device->dev)))
  goto out;

 ret = VALID_MAC_WITH_COOKIE;

out:
 return ret;
}

void wg_cookie_add_mac_to_packet(void *message, size_t len,
     struct wg_peer *peer)
{
 struct message_macs *macs = (struct message_macs *)
  ((u8 *)message + len - sizeof(*macs));

 down_write(&peer->latest_cookie.lock);
 compute_mac1(macs->mac1, message, len,
       peer->latest_cookie.message_mac1_key);
 memcpy(peer->latest_cookie.last_mac1_sent, macs->mac1, COOKIE_LEN);
 peer->latest_cookie.have_sent_mac1 = true;
 up_write(&peer->latest_cookie.lock);

 down_read(&peer->latest_cookie.lock);
 if (peer->latest_cookie.is_valid &&
     !wg_birthdate_has_expired(peer->latest_cookie.birthdate,
    COOKIE_SECRET_MAX_AGE - COOKIE_SECRET_LATENCY))
  compute_mac2(macs->mac2, message, len,
        peer->latest_cookie.cookie);
 else
  memset(macs->mac2, 0, COOKIE_LEN);
 up_read(&peer->latest_cookie.lock);
}

void wg_cookie_message_create(struct message_handshake_cookie *dst,
         struct sk_buff *skb, __le32 index,
         struct cookie_checker *checker)
{
 struct message_macs *macs = (struct message_macs *)
  ((u8 *)skb->data + skb->len - sizeof(*macs));
 u8 cookie[COOKIE_LEN];

 dst->header.type = cpu_to_le32(MESSAGE_HANDSHAKE_COOKIE);
 dst->receiver_index = index;
 get_random_bytes_wait(dst->nonce, COOKIE_NONCE_LEN);

 make_cookie(cookie, skb, checker);
 xchacha20poly1305_encrypt(dst->encrypted_cookie, cookie, COOKIE_LEN,
      macs->mac1, COOKIE_LEN, dst->nonce,
      checker->cookie_encryption_key);
}

void wg_cookie_message_consume(struct message_handshake_cookie *src,
          struct wg_device *wg)
{
 struct wg_peer *peer = NULL;
 u8 cookie[COOKIE_LEN];
 bool ret;

 if (unlikely(!wg_index_hashtable_lookup(wg->index_hashtable,
      INDEX_HASHTABLE_HANDSHAKE |
      INDEX_HASHTABLE_KEYPAIR,
      src->receiver_index, &peer)))
  return;

 down_read(&peer->latest_cookie.lock);
 if (unlikely(!peer->latest_cookie.have_sent_mac1)) {
  up_read(&peer->latest_cookie.lock);
  goto out;
 }
 ret = xchacha20poly1305_decrypt(
  cookie, src->encrypted_cookie, sizeof(src->encrypted_cookie),
  peer->latest_cookie.last_mac1_sent, COOKIE_LEN, src->nonce,
  peer->latest_cookie.cookie_decryption_key);
 up_read(&peer->latest_cookie.lock);

 if (ret) {
  down_write(&peer->latest_cookie.lock);
  memcpy(peer->latest_cookie.cookie, cookie, COOKIE_LEN);
  peer->latest_cookie.birthdate = ktime_get_coarse_boottime_ns();
  peer->latest_cookie.is_valid = true;
  peer->latest_cookie.have_sent_mac1 = false;
  up_write(&peer->latest_cookie.lock);
 } else {
  net_dbg_ratelimited("%s: Could not decrypt invalid cookie response\n",
        wg->dev->name);
 }

out:
 wg_peer_put(peer);
}