Commit ce0a89e2 authored by Nick Mathewson's avatar Nick Mathewson 🤹
Browse files

Make Tor work with OpenSSL 0.9.8l 

To fix a major security problem related to incorrect use of
SSL/TLS renegotiation, OpenSSL has turned off renegotiation by
default.  We are not affected by this security problem, however,
since we do renegotiation right.  (Specifically, we never treat a
renegotiated credential as authenticating previous communication.)
Nevertheless, OpenSSL's new behavior requires us to explicitly
turn renegotiation back on in order to get our protocol working
again.

Amusingly, this is not so simple as "set the flag when you create
the SSL object" , since calling connect or accept seems to clear
the flags.

For belt-and-suspenders purposes, we clear the flag once the Tor
handshake is done.  There's no way to exploit a second handshake
either, but we might as well not allow it.
parent 54973a45

ChangeLog

+6 −0
Original line number Original line Diff line number Diff line 
Changes in Version 0.2.1.21 - 20??-??-??

Changes in Version 0.2.1.21 - 20??-??-??

  o Major bugfixes:

    - Work around a security feature in OpenSSL 0.9.8l that prevents our

      handshake from working unless we explicitly tell OpenSSL that we are

      using SSL renegotiation safely.  We are, of course, but OpenSSL

      0.9.8l won't work unless we say we are.



  o Minor bugfixes:

  o Minor bugfixes:

    - Do not refuse to learn about authority certs and v2 networkstatus

    - Do not refuse to learn about authority certs and v2 networkstatus

      documents that are older than the latest consensus.  This bug might

      documents that are older than the latest consensus.  This bug might

src/common/tortls.c

+34 −0
Original line number Original line Diff line number Diff line
@@ -154,6 +154,7 @@ static X509* tor_tls_create_certificate(crypto_pk_env_t *rsa, 
                                        const char *cname,

                                        const char *cname,

                                        const char *cname_sign,

                                        const char *cname_sign,

                                        unsigned int lifetime);

                                        unsigned int lifetime);

static void tor_tls_unblock_renegotiation(tor_tls_t *tls);





/** Global tls context. We keep it here because nobody else needs to

/** Global tls context. We keep it here because nobody else needs to

 * touch it. */

 * touch it. */
@@ -904,6 +905,36 @@ tor_tls_set_renegotiate_callback(tor_tls_t *tls, 
#endif

#endif

}

}





/** If this version of openssl requires it, turn on renegotiation on

 * <b>tls</b>.  (Our protocol never requires this for security, but it's nice

 * to use belt-and-suspenders here.)

 */

static void

tor_tls_unblock_renegotiation(tor_tls_t *tls)

{

#ifdef SSL3_FLAGS_ALLOW_UNSAFE_LEGACY_RENEGOTIATION

  /* Yes, we know what we are doing here.  No, we do not treat a renegotiation

   * as authenticating any earlier-received data. */

  tls->ssl->s3->flags |= SSL3_FLAGS_ALLOW_UNSAFE_LEGACY_RENEGOTIATION;

#else

  (void)tls;

#endif

}



/** If this version of openssl supports it, turn off renegotiation on

 * <b>tls</b>.  (Our protocol never requires this for security, but it's nice

 * to use belt-and-suspenders here.)

 */

void

tor_tls_block_renegotiation(tor_tls_t *tls)

{

#ifdef SSL3_FLAGS_ALLOW_UNSAFE_LEGACY_RENEGOTIATION

  tls->ssl->s3->flags &= ~SSL3_FLAGS_ALLOW_UNSAFE_LEGACY_RENEGOTIATION;

#else

  (void)tls;

#endif

}



/** Return whether this tls initiated the connect (client) or

/** Return whether this tls initiated the connect (client) or

 * received it (server). */

 * received it (server). */

int

int
@@ -1026,6 +1057,9 @@ tor_tls_handshake(tor_tls_t *tls) 
  } else {

  } else {

    r = SSL_connect(tls->ssl);

    r = SSL_connect(tls->ssl);

  }

  }

  /* We need to call this here and not earlier, since OpenSSL has a penchant

   * for clearing its flags when you say accept or connect. */

  tor_tls_unblock_renegotiation(tls);

  r = tor_tls_get_error(tls,r,0, "handshaking", LOG_INFO);

  r = tor_tls_get_error(tls,r,0, "handshaking", LOG_INFO);

  if (ERR_peek_error() != 0) {

  if (ERR_peek_error() != 0) {

    tls_log_errors(tls, tls->isServer ? LOG_INFO : LOG_WARN,

    tls_log_errors(tls, tls->isServer ? LOG_INFO : LOG_WARN,

src/common/tortls.h

+1 −0
Original line number Original line Diff line number Diff line
@@ -65,6 +65,7 @@ int tor_tls_read(tor_tls_t *tls, char *cp, size_t len); 
int tor_tls_write(tor_tls_t *tls, const char *cp, size_t n);

int tor_tls_write(tor_tls_t *tls, const char *cp, size_t n);

int tor_tls_handshake(tor_tls_t *tls);

int tor_tls_handshake(tor_tls_t *tls);

int tor_tls_renegotiate(tor_tls_t *tls);

int tor_tls_renegotiate(tor_tls_t *tls);

void tor_tls_block_renegotiation(tor_tls_t *tls);

int tor_tls_shutdown(tor_tls_t *tls);

int tor_tls_shutdown(tor_tls_t *tls);

int tor_tls_get_pending_bytes(tor_tls_t *tls);

int tor_tls_get_pending_bytes(tor_tls_t *tls);

size_t tor_tls_get_forced_write_size(tor_tls_t *tls);

size_t tor_tls_get_forced_write_size(tor_tls_t *tls);

src/or/connection_or.c

+2 −0
Original line number Original line Diff line number Diff line
@@ -844,6 +844,7 @@ connection_or_tls_renegotiated_cb(tor_tls_t *tls, void *_conn) 




  /* Don't invoke this again. */

  /* Don't invoke this again. */

  tor_tls_set_renegotiate_callback(tls, NULL, NULL);

  tor_tls_set_renegotiate_callback(tls, NULL, NULL);

  tor_tls_block_renegotiation(tls);





  if (connection_tls_finish_handshake(conn) < 0) {

  if (connection_tls_finish_handshake(conn) < 0) {

    /* XXXX_TLS double-check that it's ok to do this from inside read. */

    /* XXXX_TLS double-check that it's ok to do this from inside read. */
@@ -1087,6 +1088,7 @@ connection_tls_finish_handshake(or_connection_t *conn) 
      connection_or_init_conn_from_address(conn, &conn->_base.addr,

      connection_or_init_conn_from_address(conn, &conn->_base.addr,

                                           conn->_base.port, digest_rcvd, 0);

                                           conn->_base.port, digest_rcvd, 0);

    }

    }

    tor_tls_block_renegotiation(conn->tls);

    return connection_or_set_state_open(conn);

    return connection_or_set_state_open(conn);

  } else {

  } else {

    conn->_base.state = OR_CONN_STATE_OR_HANDSHAKING;

    conn->_base.state = OR_CONN_STATE_OR_HANDSHAKING;