ssl/ssl_versions.c

/* Copyright (c) 2017, Google Inc.
 *
 * Permission to use, copy, modify, and/or distribute this software for any
 * purpose with or without fee is hereby granted, provided that the above
 * copyright notice and this permission notice appear in all copies.
 *
 * THE SOFTWARE IS PROVIDED "AS IS" AND THE AUTHOR DISCLAIMS ALL WARRANTIES
 * WITH REGARD TO THIS SOFTWARE INCLUDING ALL IMPLIED WARRANTIES OF
 * MERCHANTABILITY AND FITNESS. IN NO EVENT SHALL THE AUTHOR BE LIABLE FOR ANY
 * SPECIAL, DIRECT, INDIRECT, OR CONSEQUENTIAL DAMAGES OR ANY DAMAGES
 * WHATSOEVER RESULTING FROM LOSS OF USE, DATA OR PROFITS, WHETHER IN AN ACTION
 * OF CONTRACT, NEGLIGENCE OR OTHER TORTIOUS ACTION, ARISING OUT OF OR IN
 * CONNECTION WITH THE USE OR PERFORMANCE OF THIS SOFTWARE. */

#include <openssl/ssl.h>

#include <assert.h>

#include <openssl/bytestring.h>
#include <openssl/err.h>

#include "internal.h"
#include "../crypto/internal.h"


int ssl_protocol_version_from_wire(uint16_t *out, uint16_t version) {
  switch (version) {
    case SSL3_VERSION:
    case TLS1_VERSION:
    case TLS1_1_VERSION:
    case TLS1_2_VERSION:
      *out = version;
      return 1;

    case TLS1_3_DRAFT_VERSION:
    case TLS1_3_EXPERIMENT_VERSION:
      *out = TLS1_3_VERSION;
      return 1;

    case DTLS1_VERSION:
      /* DTLS 1.0 is analogous to TLS 1.1, not TLS 1.0. */
      *out = TLS1_1_VERSION;
      return 1;

    case DTLS1_2_VERSION:
      *out = TLS1_2_VERSION;
      return 1;

    default:
      return 0;
  }
}

/* The follow arrays are the supported versions for TLS and DTLS, in order of
 * decreasing preference. */

static const uint16_t kTLSVersions[] = {
    TLS1_3_DRAFT_VERSION,
    TLS1_3_EXPERIMENT_VERSION,
    TLS1_2_VERSION,
    TLS1_1_VERSION,
    TLS1_VERSION,
    SSL3_VERSION,
};

static const uint16_t kDTLSVersions[] = {
    DTLS1_2_VERSION,
    DTLS1_VERSION,
};

static void get_method_versions(const SSL_PROTOCOL_METHOD *method,
                                const uint16_t **out, size_t *out_num) {
  if (method->is_dtls) {
    *out = kDTLSVersions;
    *out_num = OPENSSL_ARRAY_SIZE(kDTLSVersions);
  } else {
    *out = kTLSVersions;
    *out_num = OPENSSL_ARRAY_SIZE(kTLSVersions);
  }
}

static int method_supports_version(const SSL_PROTOCOL_METHOD *method,
                                   uint16_t version) {
  const uint16_t *versions;
  size_t num_versions;
  get_method_versions(method, &versions, &num_versions);
  for (size_t i = 0; i < num_versions; i++) {
    if (versions[i] == version) {
      return 1;
    }
  }
  return 0;
}

static int set_version_bound(const SSL_PROTOCOL_METHOD *method, uint16_t *out,
                             uint16_t version) {
  /* The public API uses wire versions, except we use |TLS1_3_VERSION|
   * everywhere to refer to any draft TLS 1.3 versions. In this direction, we
   * map it to some representative TLS 1.3 draft version. */
  if (version == TLS1_3_DRAFT_VERSION ||
      version == TLS1_3_EXPERIMENT_VERSION) {
    OPENSSL_PUT_ERROR(SSL, SSL_R_UNKNOWN_SSL_VERSION);
    return 0;
  }
  if (version == TLS1_3_VERSION) {
    version = TLS1_3_DRAFT_VERSION;
  }

  if (!method_supports_version(method, version) ||
      !ssl_protocol_version_from_wire(out, version)) {
    OPENSSL_PUT_ERROR(SSL, SSL_R_UNKNOWN_SSL_VERSION);
    return 0;
  }

  return 1;
}

static int set_min_version(const SSL_PROTOCOL_METHOD *method, uint16_t *out,
                           uint16_t version) {
  /* Zero is interpreted as the default minimum version. */
  if (version == 0) {
    /* SSL 3.0 is disabled by default and TLS 1.0 does not exist in DTLS. */
    *out = method->is_dtls ? TLS1_1_VERSION : TLS1_VERSION;
    return 1;
  }

  return set_version_bound(method, out, version);
}

static int set_max_version(const SSL_PROTOCOL_METHOD *method, uint16_t *out,
                           uint16_t version) {
  /* Zero is interpreted as the default maximum version. */
  if (version == 0) {
    *out = TLS1_2_VERSION;
    return 1;
  }

  return set_version_bound(method, out, version);
}

int SSL_CTX_set_min_proto_version(SSL_CTX *ctx, uint16_t version) {
  return set_min_version(ctx->method, &ctx->conf_min_version, version);
}

int SSL_CTX_set_max_proto_version(SSL_CTX *ctx, uint16_t version) {
  return set_max_version(ctx->method, &ctx->conf_max_version, version);
}

int SSL_set_min_proto_version(SSL *ssl, uint16_t version) {
  return set_min_version(ssl->method, &ssl->conf_min_version, version);
}

int SSL_set_max_proto_version(SSL *ssl, uint16_t version) {
  return set_max_version(ssl->method, &ssl->conf_max_version, version);
}

const struct {
  uint16_t version;
  uint32_t flag;
} kProtocolVersions[] = {
    {SSL3_VERSION, SSL_OP_NO_SSLv3},
    {TLS1_VERSION, SSL_OP_NO_TLSv1},
    {TLS1_1_VERSION, SSL_OP_NO_TLSv1_1},
    {TLS1_2_VERSION, SSL_OP_NO_TLSv1_2},
    {TLS1_3_VERSION, SSL_OP_NO_TLSv1_3},
};

int ssl_get_version_range(const SSL *ssl, uint16_t *out_min_version,
                          uint16_t *out_max_version) {
  /* For historical reasons, |SSL_OP_NO_DTLSv1| aliases |SSL_OP_NO_TLSv1|, but
   * DTLS 1.0 should be mapped to TLS 1.1. */
  uint32_t options = ssl->options;
  if (SSL_is_dtls(ssl)) {
    options &= ~SSL_OP_NO_TLSv1_1;
    if (options & SSL_OP_NO_DTLSv1) {
      options |= SSL_OP_NO_TLSv1_1;
    }
  }

  uint16_t min_version = ssl->conf_min_version;
  uint16_t max_version = ssl->conf_max_version;

  /* OpenSSL's API for controlling versions entails blacklisting individual
   * protocols. This has two problems. First, on the client, the protocol can
   * only express a contiguous range of versions. Second, a library consumer
   * trying to set a maximum version cannot disable protocol versions that get
   * added in a future version of the library.
   *
   * To account for both of these, OpenSSL interprets the client-side bitmask
   * as a min/max range by picking the lowest contiguous non-empty range of
   * enabled protocols. Note that this means it is impossible to set a maximum
   * version of the higest supported TLS version in a future-proof way. */
  int any_enabled = 0;
  for (size_t i = 0; i < OPENSSL_ARRAY_SIZE(kProtocolVersions); i++) {
    /* Only look at the versions already enabled. */
    if (min_version > kProtocolVersions[i].version) {
      continue;
    }
    if (max_version < kProtocolVersions[i].version) {
      break;
    }

    if (!(options & kProtocolVersions[i].flag)) {
      /* The minimum version is the first enabled version. */
      if (!any_enabled) {
        any_enabled = 1;
        min_version = kProtocolVersions[i].version;
      }
      continue;
    }

    /* If there is a disabled version after the first enabled one, all versions
     * after it are implicitly disabled. */
    if (any_enabled) {
      max_version = kProtocolVersions[i-1].version;
      break;
    }
  }

  if (!any_enabled) {
    OPENSSL_PUT_ERROR(SSL, SSL_R_NO_SUPPORTED_VERSIONS_ENABLED);
    return 0;
  }

  *out_min_version = min_version;
  *out_max_version = max_version;
  return 1;
}

static uint16_t ssl_version(const SSL *ssl) {
  /* In early data, we report the predicted version. */
  if (SSL_in_early_data(ssl) && !ssl->server) {
    return ssl->s3->hs->early_session->ssl_version;
  }
  return ssl->version;
}

int SSL_version(const SSL *ssl) {
  uint16_t ret = ssl_version(ssl);
  /* Report TLS 1.3 draft version as TLS 1.3 in the public API. */
  if (ret == TLS1_3_DRAFT_VERSION || ret == TLS1_3_EXPERIMENT_VERSION) {
    return TLS1_3_VERSION;
  }
  return ret;
}

static const char *ssl_get_version(int version) {
  switch (version) {
    /* Report TLS 1.3 draft version as TLS 1.3 in the public API. */
    case TLS1_3_DRAFT_VERSION:
    case TLS1_3_EXPERIMENT_VERSION:
      return "TLSv1.3";

    case TLS1_2_VERSION:
      return "TLSv1.2";

    case TLS1_1_VERSION:
      return "TLSv1.1";

    case TLS1_VERSION:
      return "TLSv1";

    case SSL3_VERSION:
      return "SSLv3";

    case DTLS1_VERSION:
      return "DTLSv1";

    case DTLS1_2_VERSION:
      return "DTLSv1.2";

    default:
      return "unknown";
  }
}

const char *SSL_get_version(const SSL *ssl) {
  return ssl_get_version(ssl_version(ssl));
}

const char *SSL_SESSION_get_version(const SSL_SESSION *session) {
  return ssl_get_version(session->ssl_version);
}

uint16_t ssl3_protocol_version(const SSL *ssl) {
  assert(ssl->s3->have_version);
  uint16_t version;
  if (!ssl_protocol_version_from_wire(&version, ssl->version)) {
    /* |ssl->version| will always be set to a valid version. */
    assert(0);
    return 0;
  }

  return version;
}

int ssl_supports_version(SSL_HANDSHAKE *hs, uint16_t version) {
  SSL *const ssl = hs->ssl;
  /* As a client, only allow the configured TLS 1.3 variant. As a server,
   * support all TLS 1.3 variants as long as tls13_variant is set to a
   * non-default value. */
  if (ssl->server) {
    if (ssl->ctx->tls13_variant == tls13_default &&
        version == TLS1_3_EXPERIMENT_VERSION) {
      return 0;
    }
  } else {
    if ((ssl->ctx->tls13_variant != tls13_experiment &&
         version == TLS1_3_EXPERIMENT_VERSION) ||
        (ssl->ctx->tls13_variant != tls13_default &&
         version == TLS1_3_DRAFT_VERSION)) {
      return 0;
    }
  }

  uint16_t protocol_version;
  return method_supports_version(ssl->method, version) &&
         ssl_protocol_version_from_wire(&protocol_version, version) &&
         hs->min_version <= protocol_version &&
         protocol_version <= hs->max_version;
}

int ssl_add_supported_versions(SSL_HANDSHAKE *hs, CBB *cbb) {
  const uint16_t *versions;
  size_t num_versions;
  get_method_versions(hs->ssl->method, &versions, &num_versions);
  for (size_t i = 0; i < num_versions; i++) {
    if (ssl_supports_version(hs, versions[i]) &&
        !CBB_add_u16(cbb, versions[i])) {
      return 0;
    }
  }
  return 1;
}

int ssl_negotiate_version(SSL_HANDSHAKE *hs, uint8_t *out_alert,
                          uint16_t *out_version, const CBS *peer_versions) {
  const uint16_t *versions;
  size_t num_versions;
  get_method_versions(hs->ssl->method, &versions, &num_versions);
  for (size_t i = 0; i < num_versions; i++) {
    if (!ssl_supports_version(hs, versions[i])) {
      continue;
    }

    CBS copy = *peer_versions;
    while (CBS_len(&copy) != 0) {
      uint16_t version;
      if (!CBS_get_u16(&copy, &version)) {
        OPENSSL_PUT_ERROR(SSL, SSL_R_DECODE_ERROR);
        *out_alert = SSL_AD_DECODE_ERROR;
        return 0;
      }

      if (version == versions[i]) {
        *out_version = version;
        return 1;
      }
    }
  }

  OPENSSL_PUT_ERROR(SSL, SSL_R_UNSUPPORTED_PROTOCOL);
  *out_alert = SSL_AD_PROTOCOL_VERSION;
  return 0;
}