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/* Copyright (C) CZ.NIC, z.s.p.o. <knot-resolver@labs.nic.cz>
* SPDX-License-Identifier: GPL-3.0-or-later
*/
#include <inttypes.h>
#include <stdbool.h>
#include <stdlib.h>
#include <string.h>
#include <sys/time.h>
#include <gnutls/gnutls.h>
#include <gnutls/crypto.h>
#include <uv.h>
#include "lib/utils.h"
/* Style: "local/static" identifiers are usually named tst_* */
/** The number of seconds between synchronized rotation of TLS session ticket key. */
#define TST_KEY_LIFETIME 4096
/** Value from gnutls:lib/ext/session_ticket.c
* Beware: changing this needs to change the hashing implementation. */
#define SESSION_KEY_SIZE 64
/** Compile-time support for setting the secret. */
/* This is not secure with TLS <= 1.2 but TLS 1.3 and secure configuration
* is not available in GnuTLS yet. See https://gitlab.com/gnutls/gnutls/issues/477 */
#define TLS_SESSION_RESUMPTION_SYNC (GNUTLS_VERSION_NUMBER >= 0x030603)
#if TLS_SESSION_RESUMPTION_SYNC
#define TST_HASH GNUTLS_DIG_SHA3_512
#else
#define TST_HASH abort()
#endif
#if GNUTLS_VERSION_NUMBER < 0x030400
/* It's of little use anyway. We may get the secret through lua,
* which creates a copy outside of our control. */
#define gnutls_memset memset
#endif
/** Fields are internal to tst_key_* functions. */
typedef struct tls_session_ticket_ctx {
uv_timer_t timer; /**< timer for rotation of the key */
unsigned char key[SESSION_KEY_SIZE]; /**< the key itself */
bool has_secret; /**< false -> key is random for each epoch */
uint16_t hash_len; /**< length of `hash_data` */
char hash_data[]; /**< data to hash to obtain `key`;
* it's `time_t epoch` and then the secret string */
} tst_ctx_t;
/** Check invariants, based on gnutls version. */
static bool tst_key_invariants(void)
{
static int result = 0; /*< cache for multiple invocations */
if (result) return result > 0;
bool ok = true;
#if TLS_SESSION_RESUMPTION_SYNC
/* SHA3-512 output size may never change, but let's check it anyway :-) */
ok = ok && gnutls_hash_get_len(TST_HASH) == SESSION_KEY_SIZE;
#endif
/* The ticket key size might change in a different gnutls version. */
gnutls_datum_t key = { 0, 0 };
ok = ok && gnutls_session_ticket_key_generate(&key) == 0
&& key.size == SESSION_KEY_SIZE;
free(key.data);
result = ok ? 1 : -1;
return ok;
}
/** Create the internal structures and copy the secret. Beware: secret must be kept secure. */
static tst_ctx_t * tst_key_create(const char *secret, size_t secret_len, uv_loop_t *loop)
{
const size_t hash_len = sizeof(time_t) + secret_len;
if (kr_fails_assert(!secret_len || (secret && hash_len >= secret_len && hash_len <= UINT16_MAX))) {
return NULL;
/* reasonable secret_len is best enforced in config API */
}
if (kr_fails_assert(tst_key_invariants()))
return NULL;
#if !TLS_SESSION_RESUMPTION_SYNC
if (secret_len) {
kr_log_error(TLS, "session ticket: secrets were not enabled at compile-time (your GnuTLS version is not supported)\n");
return NULL; /* ENOTSUP */
}
#endif
tst_ctx_t *ctx = malloc(sizeof(*ctx) + hash_len); /* can be slightly longer */
if (!ctx) return NULL;
ctx->has_secret = secret_len > 0;
ctx->hash_len = hash_len;
if (secret_len) {
memcpy(ctx->hash_data + sizeof(time_t), secret, secret_len);
}
if (uv_timer_init(loop, &ctx->timer) != 0) {
free(ctx);
return NULL;
}
ctx->timer.data = ctx;
return ctx;
}
/** Random variant of secret rotation: generate into key_tmp and copy. */
static int tst_key_get_random(tst_ctx_t *ctx)
{
gnutls_datum_t key_tmp = { NULL, 0 };
int err = gnutls_session_ticket_key_generate(&key_tmp);
if (err) return kr_error(err);
if (kr_fails_assert(key_tmp.size == SESSION_KEY_SIZE))
return kr_error(EFAULT);
memcpy(ctx->key, key_tmp.data, SESSION_KEY_SIZE);
gnutls_memset(key_tmp.data, 0, SESSION_KEY_SIZE);
free(key_tmp.data);
return kr_ok();
}
/** Recompute the session ticket key, if epoch has changed or forced. */
static int tst_key_update(tst_ctx_t *ctx, time_t epoch, bool force_update)
{
if (kr_fails_assert(ctx && ctx->hash_len >= sizeof(epoch)))
return kr_error(EINVAL);
/* documented limitation: time_t and endianness must match
* on instances sharing a secret */
if (!force_update && memcmp(ctx->hash_data, &epoch, sizeof(epoch)) == 0) {
return kr_ok(); /* we are up to date */
}
memcpy(ctx->hash_data, &epoch, sizeof(epoch));
if (!ctx->has_secret) {
return tst_key_get_random(ctx);
}
/* Otherwise, deterministic variant of secret rotation, if supported. */
#if !TLS_SESSION_RESUMPTION_SYNC
kr_assert(!ENOTSUP);
return kr_error(ENOTSUP);
#else
int err = gnutls_hash_fast(TST_HASH, ctx->hash_data,
ctx->hash_len, ctx->key);
return err == 0 ? kr_ok() : kr_error(err);
#endif
}
/** Free all resources of the key (securely). */
static void tst_key_destroy(uv_handle_t *timer)
{
if (kr_fails_assert(timer))
return;
tst_ctx_t *ctx = timer->data;
if (kr_fails_assert(ctx))
return;
gnutls_memset(ctx, 0, offsetof(tst_ctx_t, hash_data) + ctx->hash_len);
free(ctx);
}
static void tst_key_check(uv_timer_t *timer, bool force_update);
static void tst_timer_callback(uv_timer_t *timer)
{
tst_key_check(timer, false);
}
/** Update the ST key if needed and reschedule itself via the timer. */
static void tst_key_check(uv_timer_t *timer, bool force_update)
{
tst_ctx_t *stst = (tst_ctx_t *)timer->data;
/* Compute the current epoch. */
struct timeval now;
if (gettimeofday(&now, NULL)) {
kr_log_error(TLS, "session ticket: gettimeofday failed, %s\n",
strerror(errno));
return;
}
uv_update_time(timer->loop); /* to have sync. between real and mono time */
const time_t epoch = now.tv_sec / TST_KEY_LIFETIME;
/* Update the key; new sessions will fetch it from the location.
* Old ones hopefully can't get broken by that; documentation
* for gnutls_session_ticket_enable_server() doesn't say. */
int err = tst_key_update(stst, epoch, force_update);
if (err) {
kr_log_error(TLS, "session ticket: failed rotation, %s\n",
kr_strerror(err));
if (kr_fails_assert(err != kr_error(EINVAL)))
return;
}
/* Reschedule. */
const time_t tv_sec_next = (epoch + 1) * TST_KEY_LIFETIME;
const uint64_t ms_until_second = 1000 - (now.tv_usec + 501) / 1000;
const uint64_t remain_ms = (tv_sec_next - now.tv_sec - 1) * (uint64_t)1000
+ ms_until_second + 1;
/* ^ +1 because we don't want to wake up half a millisecond before the epoch! */
if (kr_fails_assert(remain_ms < ((uint64_t)TST_KEY_LIFETIME + 1 /*rounding tolerance*/) * 1000))
return;
kr_log_debug(TLS, "session ticket: epoch %"PRIu64
", scheduling rotation check in %"PRIu64" ms\n",
(uint64_t)epoch, remain_ms);
err = uv_timer_start(timer, &tst_timer_callback, remain_ms, 0);
if (kr_fails_assert(err == 0)) {
kr_log_error(TLS, "session ticket: failed to schedule, %s\n",
uv_strerror(err));
return;
}
}
/* Implementation for prototypes from ./tls.h */
void tls_session_ticket_enable(struct tls_session_ticket_ctx *ctx, gnutls_session_t session)
{
if (kr_fails_assert(ctx && session))
return;
const gnutls_datum_t gd = {
.size = SESSION_KEY_SIZE,
.data = ctx->key,
};
int err = gnutls_session_ticket_enable_server(session, &gd);
if (err) {
kr_log_error(TLS, "failed to enable session tickets: %s (%d)\n",
gnutls_strerror_name(err), err);
/* but continue without tickets */
}
}
tst_ctx_t * tls_session_ticket_ctx_create(uv_loop_t *loop, const char *secret,
size_t secret_len)
{
if (kr_fails_assert(loop && (!secret_len || secret)))
return NULL;
#if GNUTLS_VERSION_NUMBER < 0x030500
/* We would need different SESSION_KEY_SIZE; avoid an error. */
return NULL;
#endif
tst_ctx_t *ctx = tst_key_create(secret, secret_len, loop);
if (ctx) {
tst_key_check(&ctx->timer, true);
}
return ctx;
}
void tls_session_ticket_ctx_destroy(tst_ctx_t *ctx)
{
if (ctx == NULL) {
return;
}
uv_close((uv_handle_t *)&ctx->timer, &tst_key_destroy);
}
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