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spread guard rotation out throughout the month

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This commit is contained in:
Roger Dingledine 2010-01-19 17:52:52 -05:00
parent 0642ab2428
commit 1fc94bfd0e
2 changed files with 17 additions and 20 deletions
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7
ChangeLog
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@ -8,6 +8,13 @@ Changes in version 0.2.1.23 - 2010-0?-??
automatically discard guards picked using the old algorithm. Fixes
bug 1217; bugfix on 0.2.1.3-alpha. Found by Mike Perry.
o Minor features:
- Avoid a mad rush at the beginning of each month when each client
rotates half of its guards. Instead we spread the rotation out
throughout the month, but we still avoid leaving a precise timestamp
in the state file about when we first picked the guard. Improves
over the behavior introduced in 0.1.2.17.
Changes in version 0.2.1.22 - 2010-01-19
Tor 0.2.1.22 fixes a critical privacy problem in bridge directory

30
src/or/circuitbuild.c
View File

@ -58,7 +58,6 @@ static int count_acceptable_routers(smartlist_t *routers);
static int onion_append_hop(crypt_path_t **head_ptr, extend_info_t *choice);
static void entry_guards_changed(void);
static time_t start_of_month(time_t when);
/** Iterate over values of circ_id, starting from conn-\>next_circ_id,
* and with the high bit specified by conn-\>circ_id_type, until we get
@ -2137,7 +2136,12 @@ add_an_entry_guard(routerinfo_t *chosen, int reset_status)
log_info(LD_CIRC, "Chose '%s' as new entry guard.", router->nickname);
strlcpy(entry->nickname, router->nickname, sizeof(entry->nickname));
memcpy(entry->identity, router->cache_info.identity_digest, DIGEST_LEN);
entry->chosen_on_date = start_of_month(time(NULL));
/* Choose expiry time smudged over the past month. The goal here
* is to a) spread out when Tor clients rotate their guards, so they
* don't all select them on the same day, and b) avoid leaving a
* precise timestamp in the state file about when we first picked
* this guard. For details, see the Jan 2010 or-dev thread. */
entry->chosen_on_date = time(NULL) - crypto_rand_int(3600*24*30);
entry->chosen_by_version = tor_strdup(VERSION);
if (chosen) /* prepend */
smartlist_insert(entry_guards, 0, entry);
@ -2188,7 +2192,7 @@ static int
remove_obsolete_entry_guards(void)
{
int changed = 0, i;
time_t this_month = start_of_month(time(NULL));
time_t now = time(NULL);
for (i = 0; i < smartlist_len(entry_guards); ++i) {
entry_guard_t *entry = smartlist_get(entry_guards, i);
@ -2220,9 +2224,8 @@ remove_obsolete_entry_guards(void)
}
tor_free(tor_ver);
}
if (!version_is_bad && entry->chosen_on_date + 3600*24*35 < this_month) {
/* It's been more than a month, and probably more like two since
* chosen_on_date is clipped to the beginning of its month. */
if (!version_is_bad && entry->chosen_on_date + 3600*24*60 < now) {
/* It's been 2 months since the date listed in our state file. */
msg = "was selected several months ago";
date_is_bad = 1;
}
@ -2673,19 +2676,6 @@ choose_random_entry(cpath_build_state_t *state)
return r;
}
/** Helper: Return the start of the month containing <b>time</b>. */
static time_t
start_of_month(time_t now)
{
struct tm tm;
tor_gmtime_r(&now, &tm);
tm.tm_sec = 0;
tm.tm_min = 0;
tm.tm_hour = 0;
tm.tm_mday = 1;
return tor_timegm(&tm);
}
/** Parse <b>state</b> and learn about the entry guards it describes.
* If <b>set</b> is true, and there are no errors, replace the global
* entry_list with what we find.
@ -2794,7 +2784,7 @@ entry_guards_parse_state(or_state_t *state, int set, char **msg)
} else {
if (state_version) {
e->chosen_by_version = tor_strdup(state_version);
e->chosen_on_date = start_of_month(time(NULL));
e->chosen_on_date = time(NULL) - crypto_rand_int(3600*24*30);
}
}
});