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sys/dev/wg/wg_cookie.c

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/* SPDX-License-Identifier: ISC
*
* Copyright (C) 2015-2021 Jason A. Donenfeld <Jason@zx2c4.com>. All Rights Reserved.
* Copyright (C) 2019-2021 Matt Dunwoodie <ncon@noconroy.net>
*/
#include "opt_inet.h"
#include "opt_inet6.h"
#include <sys/param.h>
#include <sys/systm.h>
#include <sys/kernel.h>
#include <sys/lock.h>
#include <sys/mutex.h>
#include <sys/rwlock.h>
#include <sys/socket.h>
#include <crypto/siphash/siphash.h>
#include <netinet/in.h>
#include <vm/uma.h>
#include "wg_cookie.h"
#define COOKIE_MAC1_KEY_LABEL "mac1----"
#define COOKIE_COOKIE_KEY_LABEL "cookie--"
#define COOKIE_SECRET_MAX_AGE 120
#define COOKIE_SECRET_LATENCY 5
/* Constants for initiation rate limiting */
#define RATELIMIT_SIZE (1 << 13)
#define RATELIMIT_MASK (RATELIMIT_SIZE - 1)
#define RATELIMIT_SIZE_MAX (RATELIMIT_SIZE * 8)
#define INITIATIONS_PER_SECOND 20
#define INITIATIONS_BURSTABLE 5
#define INITIATION_COST (SBT_1S / INITIATIONS_PER_SECOND)
#define TOKEN_MAX (INITIATION_COST * INITIATIONS_BURSTABLE)
#define ELEMENT_TIMEOUT 1
#define IPV4_MASK_SIZE 4 /* Use all 4 bytes of IPv4 address */
#define IPV6_MASK_SIZE 8 /* Use top 8 bytes (/64) of IPv6 address */
struct ratelimit_key {
struct vnet *vnet;
uint8_t ip[IPV6_MASK_SIZE];
};
struct ratelimit_entry {
LIST_ENTRY(ratelimit_entry) r_entry;
struct ratelimit_key r_key;
sbintime_t r_last_time; /* sbinuptime */
uint64_t r_tokens;
};
struct ratelimit {
uint8_t rl_secret[SIPHASH_KEY_LENGTH];
struct mtx rl_mtx;
struct callout rl_gc;
LIST_HEAD(, ratelimit_entry) rl_table[RATELIMIT_SIZE];
size_t rl_table_num;
};
static void precompute_key(uint8_t *,
const uint8_t[COOKIE_INPUT_SIZE], const char *);
static void macs_mac1(struct cookie_macs *, const void *, size_t,
const uint8_t[COOKIE_KEY_SIZE]);
static void macs_mac2(struct cookie_macs *, const void *, size_t,
const uint8_t[COOKIE_COOKIE_SIZE]);
static int timer_expired(sbintime_t, uint32_t, uint32_t);
static void make_cookie(struct cookie_checker *,
uint8_t[COOKIE_COOKIE_SIZE], struct sockaddr *);
static void ratelimit_init(struct ratelimit *);
static void ratelimit_deinit(struct ratelimit *);
static void ratelimit_gc_callout(void *);
static void ratelimit_gc_schedule(struct ratelimit *);
static void ratelimit_gc(struct ratelimit *, bool);
static int ratelimit_allow(struct ratelimit *, struct sockaddr *, struct vnet *);
static uint64_t siphash13(const uint8_t [SIPHASH_KEY_LENGTH], const void *, size_t);
static struct ratelimit ratelimit_v4;
#ifdef INET6
static struct ratelimit ratelimit_v6;
#endif
static uma_zone_t ratelimit_zone;
/* Public Functions */
int
cookie_init(void)
{
if ((ratelimit_zone = uma_zcreate("wg ratelimit",
sizeof(struct ratelimit_entry), NULL, NULL, NULL, NULL, 0, 0)) == NULL)
return ENOMEM;
ratelimit_init(&ratelimit_v4);
#ifdef INET6
ratelimit_init(&ratelimit_v6);
#endif
return (0);
}
void
cookie_deinit(void)
{
ratelimit_deinit(&ratelimit_v4);
#ifdef INET6
ratelimit_deinit(&ratelimit_v6);
#endif
uma_zdestroy(ratelimit_zone);
}
void
cookie_checker_init(struct cookie_checker *cc)
{
bzero(cc, sizeof(*cc));
rw_init(&cc->cc_key_lock, "cookie_checker_key");
mtx_init(&cc->cc_secret_mtx, "cookie_checker_secret", NULL, MTX_DEF);
}
void
cookie_checker_free(struct cookie_checker *cc)
{
rw_destroy(&cc->cc_key_lock);
mtx_destroy(&cc->cc_secret_mtx);
explicit_bzero(cc, sizeof(*cc));
}
void
cookie_checker_update(struct cookie_checker *cc,
const uint8_t key[COOKIE_INPUT_SIZE])
{
rw_wlock(&cc->cc_key_lock);
if (key) {
precompute_key(cc->cc_mac1_key, key, COOKIE_MAC1_KEY_LABEL);
precompute_key(cc->cc_cookie_key, key, COOKIE_COOKIE_KEY_LABEL);
} else {
bzero(cc->cc_mac1_key, sizeof(cc->cc_mac1_key));
bzero(cc->cc_cookie_key, sizeof(cc->cc_cookie_key));
}
rw_wunlock(&cc->cc_key_lock);
}
void
cookie_checker_create_payload(struct cookie_checker *cc,
struct cookie_macs *macs, uint8_t nonce[COOKIE_NONCE_SIZE],
uint8_t ecookie[COOKIE_ENCRYPTED_SIZE], struct sockaddr *sa)
{
uint8_t cookie[COOKIE_COOKIE_SIZE];
make_cookie(cc, cookie, sa);
arc4random_buf(nonce, COOKIE_NONCE_SIZE);
rw_rlock(&cc->cc_key_lock);
xchacha20poly1305_encrypt(ecookie, cookie, COOKIE_COOKIE_SIZE,
macs->mac1, COOKIE_MAC_SIZE, nonce, cc->cc_cookie_key);
rw_runlock(&cc->cc_key_lock);
explicit_bzero(cookie, sizeof(cookie));
}
void
cookie_maker_init(struct cookie_maker *cm, const uint8_t key[COOKIE_INPUT_SIZE])
{
bzero(cm, sizeof(*cm));
precompute_key(cm->cm_mac1_key, key, COOKIE_MAC1_KEY_LABEL);
precompute_key(cm->cm_cookie_key, key, COOKIE_COOKIE_KEY_LABEL);
rw_init(&cm->cm_lock, "cookie_maker");
}
void
cookie_maker_free(struct cookie_maker *cm)
{
rw_destroy(&cm->cm_lock);
explicit_bzero(cm, sizeof(*cm));
}
int
cookie_maker_consume_payload(struct cookie_maker *cm,
uint8_t nonce[COOKIE_NONCE_SIZE], uint8_t ecookie[COOKIE_ENCRYPTED_SIZE])
{
uint8_t cookie[COOKIE_COOKIE_SIZE];
int ret;
rw_rlock(&cm->cm_lock);
if (!cm->cm_mac1_sent) {
ret = ETIMEDOUT;
goto error;
}
if (!xchacha20poly1305_decrypt(cookie, ecookie, COOKIE_ENCRYPTED_SIZE,
cm->cm_mac1_last, COOKIE_MAC_SIZE, nonce, cm->cm_cookie_key)) {
ret = EINVAL;
goto error;
}
rw_runlock(&cm->cm_lock);
rw_wlock(&cm->cm_lock);
memcpy(cm->cm_cookie, cookie, COOKIE_COOKIE_SIZE);
cm->cm_cookie_birthdate = getsbinuptime();
cm->cm_cookie_valid = true;
cm->cm_mac1_sent = false;
rw_wunlock(&cm->cm_lock);
return 0;
error:
rw_runlock(&cm->cm_lock);
return ret;
}
void
cookie_maker_mac(struct cookie_maker *cm, struct cookie_macs *macs, void *buf,
size_t len)
{
rw_wlock(&cm->cm_lock);
macs_mac1(macs, buf, len, cm->cm_mac1_key);
memcpy(cm->cm_mac1_last, macs->mac1, COOKIE_MAC_SIZE);
cm->cm_mac1_sent = true;
if (cm->cm_cookie_valid &&
!timer_expired(cm->cm_cookie_birthdate,
COOKIE_SECRET_MAX_AGE - COOKIE_SECRET_LATENCY, 0)) {
macs_mac2(macs, buf, len, cm->cm_cookie);
} else {
bzero(macs->mac2, COOKIE_MAC_SIZE);
cm->cm_cookie_valid = false;
}
rw_wunlock(&cm->cm_lock);
}
int
cookie_checker_validate_macs(struct cookie_checker *cc, struct cookie_macs *macs,
void *buf, size_t len, bool check_cookie, struct sockaddr *sa, struct vnet *vnet)
{
struct cookie_macs our_macs;
uint8_t cookie[COOKIE_COOKIE_SIZE];
/* Validate incoming MACs */
rw_rlock(&cc->cc_key_lock);
macs_mac1(&our_macs, buf, len, cc->cc_mac1_key);
rw_runlock(&cc->cc_key_lock);
/* If mac1 is invald, we want to drop the packet */
if (timingsafe_bcmp(our_macs.mac1, macs->mac1, COOKIE_MAC_SIZE) != 0)
return EINVAL;
if (check_cookie) {
make_cookie(cc, cookie, sa);
macs_mac2(&our_macs, buf, len, cookie);
/* If the mac2 is invalid, we want to send a cookie response */
if (timingsafe_bcmp(our_macs.mac2, macs->mac2, COOKIE_MAC_SIZE) != 0)
return EAGAIN;
/* If the mac2 is valid, we may want rate limit the peer.
* ratelimit_allow will return either 0 or ECONNREFUSED,
* implying there is no ratelimiting, or we should ratelimit
* (refuse) respectively. */
if (sa->sa_family == AF_INET)
return ratelimit_allow(&ratelimit_v4, sa, vnet);
#ifdef INET6
else if (sa->sa_family == AF_INET6)
return ratelimit_allow(&ratelimit_v6, sa, vnet);
#endif
else
return EAFNOSUPPORT;
}
return 0;
}
/* Private functions */
static void
precompute_key(uint8_t *key, const uint8_t input[COOKIE_INPUT_SIZE],
const char *label)
{
struct blake2s_state blake;
blake2s_init(&blake, COOKIE_KEY_SIZE);
blake2s_update(&blake, label, strlen(label));
blake2s_update(&blake, input, COOKIE_INPUT_SIZE);
blake2s_final(&blake, key);
}
static void
macs_mac1(struct cookie_macs *macs, const void *buf, size_t len,
const uint8_t key[COOKIE_KEY_SIZE])
{
struct blake2s_state state;
blake2s_init_key(&state, COOKIE_MAC_SIZE, key, COOKIE_KEY_SIZE);
blake2s_update(&state, buf, len);
blake2s_final(&state, macs->mac1);
}
static void
macs_mac2(struct cookie_macs *macs, const void *buf, size_t len,
const uint8_t key[COOKIE_COOKIE_SIZE])
{
struct blake2s_state state;
blake2s_init_key(&state, COOKIE_MAC_SIZE, key, COOKIE_COOKIE_SIZE);
blake2s_update(&state, buf, len);
blake2s_update(&state, macs->mac1, COOKIE_MAC_SIZE);
blake2s_final(&state, macs->mac2);
}
static __inline int
timer_expired(sbintime_t timer, uint32_t sec, uint32_t nsec)
{
sbintime_t now = getsbinuptime();
return (now > (timer + sec * SBT_1S + nstosbt(nsec))) ? ETIMEDOUT : 0;
}
static void
make_cookie(struct cookie_checker *cc, uint8_t cookie[COOKIE_COOKIE_SIZE],
struct sockaddr *sa)
{
struct blake2s_state state;
mtx_lock(&cc->cc_secret_mtx);
if (timer_expired(cc->cc_secret_birthdate,
COOKIE_SECRET_MAX_AGE, 0)) {
arc4random_buf(cc->cc_secret, COOKIE_SECRET_SIZE);
cc->cc_secret_birthdate = getsbinuptime();
}
blake2s_init_key(&state, COOKIE_COOKIE_SIZE, cc->cc_secret,
COOKIE_SECRET_SIZE);
mtx_unlock(&cc->cc_secret_mtx);
if (sa->sa_family == AF_INET) {
blake2s_update(&state, (uint8_t *)&satosin(sa)->sin_addr,
sizeof(struct in_addr));
blake2s_update(&state, (uint8_t *)&satosin(sa)->sin_port,
sizeof(in_port_t));
blake2s_final(&state, cookie);
#ifdef INET6
} else if (sa->sa_family == AF_INET6) {
blake2s_update(&state, (uint8_t *)&satosin6(sa)->sin6_addr,
sizeof(struct in6_addr));
blake2s_update(&state, (uint8_t *)&satosin6(sa)->sin6_port,
sizeof(in_port_t));
blake2s_final(&state, cookie);
#endif
} else {
arc4random_buf(cookie, COOKIE_COOKIE_SIZE);
}
}
static void
ratelimit_init(struct ratelimit *rl)
{
size_t i;
mtx_init(&rl->rl_mtx, "ratelimit_lock", NULL, MTX_DEF);
callout_init_mtx(&rl->rl_gc, &rl->rl_mtx, 0);
arc4random_buf(rl->rl_secret, sizeof(rl->rl_secret));
for (i = 0; i < RATELIMIT_SIZE; i++)
LIST_INIT(&rl->rl_table[i]);
rl->rl_table_num = 0;
}
static void
ratelimit_deinit(struct ratelimit *rl)
{
mtx_lock(&rl->rl_mtx);
callout_stop(&rl->rl_gc);
ratelimit_gc(rl, true);
mtx_unlock(&rl->rl_mtx);
mtx_destroy(&rl->rl_mtx);
}
static void
ratelimit_gc_callout(void *_rl)
{
/* callout will lock rl_mtx for us */
ratelimit_gc(_rl, false);
}
static void
ratelimit_gc_schedule(struct ratelimit *rl)
{
/* Trigger another GC if needed. There is no point calling GC if there
* are no entries in the table. We also want to ensure that GC occurs
* on a regular interval, so don't override a currently pending GC.
*
* In the case of a forced ratelimit_gc, there will be no entries left
* so we will will not schedule another GC. */
if (rl->rl_table_num > 0 && !callout_pending(&rl->rl_gc))
callout_reset(&rl->rl_gc, ELEMENT_TIMEOUT * hz,
ratelimit_gc_callout, rl);
}
static void
ratelimit_gc(struct ratelimit *rl, bool force)
{
size_t i;
struct ratelimit_entry *r, *tr;
sbintime_t expiry;
mtx_assert(&rl->rl_mtx, MA_OWNED);
if (rl->rl_table_num == 0)
return;
expiry = getsbinuptime() - ELEMENT_TIMEOUT * SBT_1S;
for (i = 0; i < RATELIMIT_SIZE; i++) {
LIST_FOREACH_SAFE(r, &rl->rl_table[i], r_entry, tr) {
if (r->r_last_time < expiry || force) {
rl->rl_table_num--;
LIST_REMOVE(r, r_entry);
uma_zfree(ratelimit_zone, r);
}
}
}
ratelimit_gc_schedule(rl);
}
static int
ratelimit_allow(struct ratelimit *rl, struct sockaddr *sa, struct vnet *vnet)
{
uint64_t bucket, tokens;
sbintime_t diff, now;
struct ratelimit_entry *r;
int ret = ECONNREFUSED;
struct ratelimit_key key = { .vnet = vnet };
size_t len = sizeof(key);
if (sa->sa_family == AF_INET) {
memcpy(key.ip, &satosin(sa)->sin_addr, IPV4_MASK_SIZE);
len -= IPV6_MASK_SIZE - IPV4_MASK_SIZE;
}
#ifdef INET6
else if (sa->sa_family == AF_INET6)
memcpy(key.ip, &satosin6(sa)->sin6_addr, IPV6_MASK_SIZE);
#endif
else
return ret;
bucket = siphash13(rl->rl_secret, &key, len) & RATELIMIT_MASK;
mtx_lock(&rl->rl_mtx);
LIST_FOREACH(r, &rl->rl_table[bucket], r_entry) {
if (bcmp(&r->r_key, &key, len) != 0)
continue;
/* If we get to here, we've found an entry for the endpoint.
* We apply standard token bucket, by calculating the time
* lapsed since our last_time, adding that, ensuring that we
* cap the tokens at TOKEN_MAX. If the endpoint has no tokens
* left (that is tokens <= INITIATION_COST) then we block the
* request, otherwise we subtract the INITITIATION_COST and
* return OK. */
now = getsbinuptime();
diff = now - r->r_last_time;
r->r_last_time = now;
tokens = r->r_tokens + diff;
if (tokens > TOKEN_MAX)
tokens = TOKEN_MAX;
if (tokens >= INITIATION_COST) {
r->r_tokens = tokens - INITIATION_COST;
goto ok;
} else {
r->r_tokens = tokens;
goto error;
}
}
/* If we get to here, we didn't have an entry for the endpoint, let's
* add one if we have space. */
if (rl->rl_table_num >= RATELIMIT_SIZE_MAX)
goto error;
/* Goto error if out of memory */
if ((r = uma_zalloc(ratelimit_zone, M_NOWAIT | M_ZERO)) == NULL)
goto error;
rl->rl_table_num++;
/* Insert entry into the hashtable and ensure it's initialised */
LIST_INSERT_HEAD(&rl->rl_table[bucket], r, r_entry);
r->r_key = key;
r->r_last_time = getsbinuptime();
r->r_tokens = TOKEN_MAX - INITIATION_COST;
/* If we've added a new entry, let's trigger GC. */
ratelimit_gc_schedule(rl);
ok:
ret = 0;
error:
mtx_unlock(&rl->rl_mtx);
return ret;
}
static uint64_t siphash13(const uint8_t key[SIPHASH_KEY_LENGTH], const void *src, size_t len)
{
SIPHASH_CTX ctx;
return (SipHashX(&ctx, 1, 3, key, src, len));
}
#ifdef SELFTESTS
#include "selftest/cookie.c"
#endif /* SELFTESTS */