Commit 2e2f3a4d authored by Nick Mathewson's avatar Nick Mathewson 🥔
Browse files

Add a separate, non-fractional, limit to the sampled guard set size. 

Letting the maximum sample size grow proportionally to the number of
guards defeats its purpose to a certain extent.  Noted by asn during
code review.

Fixes bug 20920; bug not in any released (or merged) version of Tor.
parent e50d85b9

src/or/entrynodes.c

+13 −1
Original line number Diff line number Diff line
@@ -401,6 +401,16 @@ get_max_sample_threshold(void) 
                            1, 100);

  return pct / 100.0;

}

/**

 * We never let our sampled guard set grow larger than this number.

 */

STATIC int

get_max_sample_size_absolute(void)

{

  return (int) networkstatus_get_param(NULL, "guard-max-sample-size",

                                       DFLT_MAX_SAMPLE_SIZE,

                                       1, INT32_MAX);

}

/**

 * We always try to make our sample contain at least this many guards.

 *
@@ -937,7 +947,9 @@ get_max_sample_size(guard_selection_t *gs, 
  if (using_bridges)

    return n_guards;



  const int max_sample = (int)(n_guards * get_max_sample_threshold());

  const int max_sample_by_pct = (int)(n_guards * get_max_sample_threshold());

  const int max_sample_absolute = get_max_sample_size_absolute();

  const int max_sample = MIN(max_sample_by_pct, max_sample_absolute);

  if (max_sample < min_sample) // XXXX prop271 spec deviation

    return min_sample;

  else

src/or/entrynodes.h

+7 −1
Original line number Diff line number Diff line
@@ -440,7 +440,12 @@ int num_bridges_usable(void); 
 * We never let our sampled guard set grow larger than this percentage

 * of the guards on the network.

 */

#define DFLT_MAX_SAMPLE_THRESHOLD_PERCENT 30

#define DFLT_MAX_SAMPLE_THRESHOLD_PERCENT 20

/**

 * We never let our sampled guard set grow larger than this number of

 * guards.

 */

#define DFLT_MAX_SAMPLE_SIZE 60

/**

 * We always try to make our sample contain at least this many guards.

 *
@@ -495,6 +500,7 @@ int num_bridges_usable(void); 
/**@}*/



STATIC double get_max_sample_threshold(void);

STATIC int get_max_sample_size_absolute(void);

STATIC int get_min_filtered_sample_size(void);

STATIC int get_remove_unlisted_guards_after_days(void);

STATIC int get_guard_lifetime_days(void);