Commit 0ff86042 authored by Mike Perry's avatar Mike Perry
Browse files

Implement new Wxx constraints. 

Cases 1 and 3b are provably correct. Case 2b has a fallback to first try to
maximize entropy.
parent 9b49a894

src/or/dirvote.c

+273 −6
Original line number Diff line number Diff line
@@ -50,7 +50,7 @@ static int dirvote_publish_consensus(void); 
static char *make_consensus_method_list(int low, int high, const char *sep);



/** The highest consensus method that we currently support. */

#define MAX_SUPPORTED_CONSENSUS_METHOD 9

#define MAX_SUPPORTED_CONSENSUS_METHOD 10



/** Lowest consensus method that contains a 'directory-footer' marker */

#define MIN_METHOD_FOR_FOOTER 9
@@ -766,15 +766,275 @@ networkstatus_check_weights(int64_t Wgg, int64_t Wgd, int64_t Wmg, 
  if (berr) {

    log_info(LD_DIR,

             "Bw weight mismatch %d. G="I64_FORMAT" M="I64_FORMAT

             " E="I64_FORMAT" D="I64_FORMAT" T="I64_FORMAT,

             " E="I64_FORMAT" D="I64_FORMAT" T="I64_FORMAT

             " Wmd=%d Wme=%d Wmg=%d Wed=%d Wee=%d"

             " Wgd=%d Wgg=%d Wme=%d Wmg=%d",

             berr,

             I64_PRINTF_ARG(G), I64_PRINTF_ARG(M), I64_PRINTF_ARG(E),

             I64_PRINTF_ARG(D), I64_PRINTF_ARG(T));

             I64_PRINTF_ARG(D), I64_PRINTF_ARG(T),

             (int)Wmd, (int)Wme, (int)Wmg, (int)Wed, (int)Wee,

             (int)Wgd, (int)Wgg, (int)Wme, (int)Wmg);

  }



  return berr;

}



/**

 * This function computes the bandwidth weights for consensus method 10.

 *

 * It returns true if weights could be computed, false otherwise.

 */

static int

networkstatus_compute_bw_weights_v10(smartlist_t *chunks, int64_t G,

                                     int64_t M, int64_t E, int64_t D,

                                     int64_t T, int64_t weight_scale)

{

  bw_weights_error_t berr = 0;

  int64_t Wgg = -1, Wgd = -1;

  int64_t Wmg = -1, Wme = -1, Wmd = -1;

  int64_t Wed = -1, Wee = -1;

  const char *casename;

  char buf[512];

  int r;



  if (G <= 0 || M <= 0 || E <= 0 || D <= 0) {

    log_warn(LD_DIR, "Consensus with empty bandwidth: "

                     "G="I64_FORMAT" M="I64_FORMAT" E="I64_FORMAT

                     " D="I64_FORMAT" T="I64_FORMAT,

             I64_PRINTF_ARG(G), I64_PRINTF_ARG(M), I64_PRINTF_ARG(E),

             I64_PRINTF_ARG(D), I64_PRINTF_ARG(T));

    return 0;

  }



  /*

   * Computed from cases in 3.4.3 of dir-spec.txt

   *

   * 1. Neither are scarce

   * 2. Both Guard and Exit are scarce

   *    a. R+D <= S

   *    b. R+D > S

   * 3. One of Guard or Exit is scarce

   *    a. S+D < T/3

   *    b. S+D >= T/3

   */

  if (3*E >= T && 3*G >= T) { // E >= T/3 && G >= T/3

    /* Case 1: Neither are scarce.  */

    casename = "Case 1 (Wgd=Wmd=Wed)";

    Wgd = weight_scale/3;

    Wed = weight_scale/3;

    Wmd = weight_scale/3;

    Wee = (weight_scale*(E+G+M))/(3*E);

    Wme = weight_scale - Wee;

    Wmg = (weight_scale*(2*G-E-M))/(3*G);

    Wgg = weight_scale - Wmg;



    berr = networkstatus_check_weights(Wgg, Wgd, Wmg, Wme, Wmd, Wee, Wed,

                                       weight_scale, G, M, E, D, T, 10, 1);



    if (berr) {

      log_warn(LD_DIR,

             "Bw Weights error %d for %s v10. G="I64_FORMAT" M="I64_FORMAT

             " E="I64_FORMAT" D="I64_FORMAT" T="I64_FORMAT

             " Wmd=%d Wme=%d Wmg=%d Wed=%d Wee=%d"

             " Wgd=%d Wgg=%d Wme=%d Wmg=%d weight_scale=%d",

             berr, casename,

             I64_PRINTF_ARG(G), I64_PRINTF_ARG(M), I64_PRINTF_ARG(E),

             I64_PRINTF_ARG(D), I64_PRINTF_ARG(T),

             (int)Wmd, (int)Wme, (int)Wmg, (int)Wed, (int)Wee,

             (int)Wgd, (int)Wgg, (int)Wme, (int)Wmg, (int)weight_scale);

      return 0;

    }

  } else if (3*E < T && 3*G < T) { // E < T/3 && G < T/3

    int64_t R = MIN(E, G);

    int64_t S = MAX(E, G);

    /*

     * Case 2: Both Guards and Exits are scarce

     * Balance D between E and G, depending upon

     * D capacity and scarcity.

     */

    if (R+D < S) { // Subcase a

      Wgg = weight_scale;

      Wee = weight_scale;

      Wmg = 0;

      Wme = 0;

      Wmd = 0;

      if (E < G) {

        casename = "Case 2a (E scarce)";

        Wed = weight_scale;

        Wgd = 0;

      } else { /* E >= G */

        casename = "Case 2a (G scarce)";

        Wed = 0;

        Wgd = weight_scale;

      }

    } else { // Subcase b: R+D >= S

      casename = "Case 2b1 (Wgg=1, Wmd=Wgd)";

      Wee = (weight_scale*(E - G + M))/E;

      Wed = (weight_scale*(D - 2*E + 4*G - 2*M))/(3*D);

      Wme = (weight_scale*(G-M))/E;

      Wmg = 0;

      Wgg = weight_scale;

      Wmd = (weight_scale - Wed)/2;

      Wgd = (weight_scale - Wed)/2;



      berr = networkstatus_check_weights(Wgg, Wgd, Wmg, Wme, Wmd, Wee, Wed,

                                       weight_scale, G, M, E, D, T, 10, 1);



      if (berr) {

        casename = "Case 2b2 (Wgg=1, Wee=1)";

        Wgg = weight_scale;

        Wee = weight_scale;

        Wed = (weight_scale*(D - 2*E + G + M))/(3*D);

        Wmd = (weight_scale*(D - 2*M + G + E))/(3*D);

        Wme = 0;

        Wmg = 0;



        if (Wmd < 0) { // Can happen if M > T/3

          casename = "Case 2b3 (Wmd=0)";

          Wmd = 0;

          log_warn(LD_DIR,

                   "Too much Middle bandwidth on the network to calculate "

                   "balanced bandwidth-weights. Consider increasing the "

                   "number of Guard nodes by lowering the requirements.");

        }

        Wgd = weight_scale - Wed - Wmd;

        berr = networkstatus_check_weights(Wgg, Wgd, Wmg, Wme, Wmd, Wee,

                  Wed, weight_scale, G, M, E, D, T, 10, 1);

      }

      if (berr != BW_WEIGHTS_NO_ERROR &&

              berr != BW_WEIGHTS_BALANCE_MID_ERROR) {

        log_warn(LD_DIR,

             "Bw Weights error %d for %s v10. G="I64_FORMAT" M="I64_FORMAT

             " E="I64_FORMAT" D="I64_FORMAT" T="I64_FORMAT

             " Wmd=%d Wme=%d Wmg=%d Wed=%d Wee=%d"

             " Wgd=%d Wgg=%d Wme=%d Wmg=%d weight_scale=%d",

             berr, casename,

             I64_PRINTF_ARG(G), I64_PRINTF_ARG(M), I64_PRINTF_ARG(E),

             I64_PRINTF_ARG(D), I64_PRINTF_ARG(T),

             (int)Wmd, (int)Wme, (int)Wmg, (int)Wed, (int)Wee,

             (int)Wgd, (int)Wgg, (int)Wme, (int)Wmg, (int)weight_scale);

        return 0;

      }

    }

  } else { // if (E < T/3 || G < T/3) {

    int64_t S = MIN(E, G);

    // Case 3: Exactly one of Guard or Exit is scarce

    if (!(3*E < T || 3*G < T) || !(3*G >= T || 3*E >= T)) {

      log_warn(LD_BUG,

           "Bw-Weights Case 3 v10 but with G="I64_FORMAT" M="

           I64_FORMAT" E="I64_FORMAT" D="I64_FORMAT" T="I64_FORMAT,

               I64_PRINTF_ARG(G), I64_PRINTF_ARG(M), I64_PRINTF_ARG(E),

               I64_PRINTF_ARG(D), I64_PRINTF_ARG(T));

    }



    if (3*(S+D) < T) { // Subcase a: S+D < T/3

      if (G < E) {

        casename = "Case 3a (G scarce)";

        Wgg = Wgd = weight_scale;

        Wmd = Wed = Wmg = 0;

        // Minor subcase, if E is more scarce than M,

        // keep its bandwidth in place.

        if (E < M) Wme = 0;

        else Wme = (weight_scale*(E-M))/(2*E);

        Wee = weight_scale-Wme;

      } else { // G >= E

        casename = "Case 3a (E scarce)";

        Wee = Wed = weight_scale;

        Wmd = Wgd = Wme = 0;

        // Minor subcase, if G is more scarce than M,

        // keep its bandwidth in place.

        if (G < M) Wmg = 0;

        else Wmg = (weight_scale*(G-M))/(2*G);

        Wgg = weight_scale-Wmg;

      }

    } else { // Subcase b: S+D >= T/3

      // D != 0 because S+D >= T/3

      if (G < E) {

        casename = "Case 3bg (G scarce, Wgg=1, Wmd == Wed)";

        Wgg = weight_scale;

        Wgd = (weight_scale*(D - 2*G + E + M))/(3*D);

        Wmg = 0;

        Wee = (weight_scale*(E+M))/(2*E);

        Wme = weight_scale - Wee;

        Wmd = (weight_scale - Wgd)/2;

        Wed = (weight_scale - Wgd)/2;



        berr = networkstatus_check_weights(Wgg, Wgd, Wmg, Wme, Wmd, Wee,

                    Wed, weight_scale, G, M, E, D, T, 10, 1);

      } else { // G >= E

        casename = "Case 3be (E scarce, Wee=1, Wmd == Wgd)";

        Wee = weight_scale;

        Wed = (weight_scale*(D - 2*E + G + M))/(3*D);

        Wme = 0;

        Wgg = (weight_scale*(G+M))/(2*G);

        Wmg = weight_scale - Wgg;

        Wmd = (weight_scale - Wed)/2;

        Wgd = (weight_scale - Wed)/2;



        berr = networkstatus_check_weights(Wgg, Wgd, Wmg, Wme, Wmd, Wee,

                      Wed, weight_scale, G, M, E, D, T, 10, 1);

      }

      if (berr) {

        log_warn(LD_DIR,

             "Bw Weights error %d for %s v10. G="I64_FORMAT" M="I64_FORMAT

             " E="I64_FORMAT" D="I64_FORMAT" T="I64_FORMAT

             " Wmd=%d Wme=%d Wmg=%d Wed=%d Wee=%d"

             " Wgd=%d Wgg=%d Wme=%d Wmg=%d weight_scale=%d",

             berr, casename,

             I64_PRINTF_ARG(G), I64_PRINTF_ARG(M), I64_PRINTF_ARG(E),

             I64_PRINTF_ARG(D), I64_PRINTF_ARG(T),

             (int)Wmd, (int)Wme, (int)Wmg, (int)Wed, (int)Wee,

             (int)Wgd, (int)Wgg, (int)Wme, (int)Wmg, (int)weight_scale);

        return 0;

      }

    }

  }



  /* We cast down the weights to 32 bit ints on the assumption that

   * weight_scale is ~= 10000. We need to ensure a rogue authority

   * doesn't break this assumption to rig our weights */

  tor_assert(0 < weight_scale && weight_scale < INT32_MAX);



  /*

   * Provide Wgm=Wgg, Wmm=1, Wem=Wee, Weg=Wed. May later determine

   * that middle nodes need different bandwidth weights for dirport traffic,

   * or that weird exit policies need special weight, or that bridges

   * need special weight.

   *

   * NOTE: This list is sorted.

   */

  r = tor_snprintf(buf, sizeof(buf),

     "bandwidth-weights Wbd=%d Wbe=%d Wbg=%d Wbm=%d "

     "Wdb=%d "

     "Web=%d Wed=%d Wee=%d Weg=%d Wem=%d "

     "Wgb=%d Wgd=%d Wgg=%d Wgm=%d "

     "Wmb=%d Wmd=%d Wme=%d Wmg=%d Wmm=%d\n",

     (int)Wmd, (int)Wme, (int)Wmg, (int)weight_scale,

     (int)weight_scale,

     (int)weight_scale, (int)Wed, (int)Wee, (int)Wed, (int)Wee,

     (int)weight_scale, (int)Wgd, (int)Wgg, (int)Wgg,

     (int)weight_scale, (int)Wmd, (int)Wme, (int)Wmg, (int)weight_scale);

  if (r<0) {

    log_warn(LD_BUG,

             "Not enough space in buffer for bandwidth-weights line.");

    *buf = '\0';

    return 0;

  }

  smartlist_add(chunks, tor_strdup(buf));



  log_notice(LD_CIRC, "Computed bandwidth weights for %s with v10: "

             "G="I64_FORMAT" M="I64_FORMAT" E="I64_FORMAT" D="I64_FORMAT

             " T="I64_FORMAT,

             casename,

             I64_PRINTF_ARG(G), I64_PRINTF_ARG(M), I64_PRINTF_ARG(E),

             I64_PRINTF_ARG(D), I64_PRINTF_ARG(T));

  return 1;

}

/**

 * This function computes the bandwidth weights for consensus method 9.

 *

 * It has been obsoleted in favor of consensus method 10.

 */

static void

networkstatus_compute_bw_weights_v9(smartlist_t *chunks, int64_t G, int64_t M,

                              int64_t E, int64_t D, int64_t T,
@@ -1064,7 +1324,7 @@ networkstatus_compute_bw_weights_v9(smartlist_t *chunks, int64_t G, int64_t M, 
    *buf = '\0';

  }

  smartlist_add(chunks, tor_strdup(buf));

  log_notice(LD_CIRC, "Computed bandwidth weights for %s: "

  log_notice(LD_CIRC, "Computed bandwidth weights for %s with v9: "

             "G="I64_FORMAT" M="I64_FORMAT" E="I64_FORMAT" D="I64_FORMAT

             " T="I64_FORMAT,

             casename,
@@ -1101,6 +1361,7 @@ networkstatus_compute_consensus(smartlist_t *votes, 
  const routerstatus_format_type_t rs_format =

    flavor == FLAV_NS ? NS_V3_CONSENSUS : NS_V3_CONSENSUS_MICRODESC;

  char *params = NULL;

  int added_weights = 0;

  tor_assert(flavor == FLAV_NS || flavor == FLAV_MICRODESC);

  tor_assert(total_authorities >= smartlist_len(votes));
@@ -1783,7 +2044,13 @@ networkstatus_compute_consensus(smartlist_t *votes, 
      }

    }



    if (consensus_method < 10) {

      networkstatus_compute_bw_weights_v9(chunks, G, M, E, D, T, weight_scale);

      added_weights = 1;

    } else {

      added_weights = networkstatus_compute_bw_weights_v10(chunks, G, M, E, D,

                                                           T, weight_scale);

    }

  }



  /* Add a signature. */
@@ -1873,7 +2140,7 @@ networkstatus_compute_consensus(smartlist_t *votes, 
      return NULL;

    }

    // Verify balancing parameters

    if (consensus_method >= MIN_METHOD_FOR_BW_WEIGHTS) {

    if (consensus_method >= MIN_METHOD_FOR_BW_WEIGHTS && added_weights) {

      networkstatus_verify_bw_weights(c);

    }

    networkstatus_vote_free(c);