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Don't obsolete a very-new connection for having no circuits yet.

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This fixes the last known case of bug 891, which could happen if two
hosts, A and B, disagree about how long a circuit has been open,
because of clock drift of some kind.  Host A would then mark the
connection as is_bad_for_new_circs when it got too old and open a new
connection.  In between when B receives a NETINFO cell on the new
conn, and when B receives a conn cell on the new circuit, the new
circuit will seem worse to B than the old one, and so B will mark it
as is_bad_for_new_circs in the second or third loop of
connection_or_group_set_badness().

Bugfix on 0.1.1.13-alpha.  Bug found by rovv.

Not a backport candidate: the bug is too obscure and the fix too tricky.

svn:r18303
This commit is contained in:
Nick Mathewson 2009-01-28 17:36:41 +00:00
parent 62a460d55f
commit e06de61d84
2 changed files with 42 additions and 14 deletions
Show Stats Download Patch File Download Diff File Expand all files Collapse all files

5
ChangeLog
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@ -15,6 +15,11 @@ Changes in version 0.2.1.12-alpha - 2009-02-??
headers. Bugfix on 0.2.0.10-alpha.
- Don't consider consider expiring already-closed client connections.
Fixes bug 893. Bugfix on 0.0.2pre20.
- Fix another interesting corner-case of bug 891 spotted by rovv:
Previously, if two hosts had different amounts of clock drift, and one
of them created a new connection with just the wrong timing, the other
might decide to deprecate the new connection erroneously. Bugfix on
0.1.1.13-alpha.
o Minor features:
- Support platforms where time_t is 64 bits long. (Congratulations,

51
src/or/connection_or.c
View File

@ -441,12 +441,21 @@ connection_or_init_conn_from_address(or_connection_t *conn,
*
* Requires that both input connections are open; not is_bad_for_new_circs,
* and not impossibly non-canonical.
*
* If </b>forgive_new_connections</b> is true, then we do not call
* <b>a</b>better than <b>b</b> simply because b has no circuits,
* unless b is also relatively old.
*/
static int
connection_or_is_better(const or_connection_t *a,
const or_connection_t *b)
connection_or_is_better(time_t now,
const or_connection_t *a,
const or_connection_t *b,
int forgive_new_connections)
{
int newer;
/** Do not definitively deprecate a new connection with no circuits on it
* until this much time has passed. */
#define NEW_CONN_GRACE_PERIOD (15*60)
if (b->is_canonical && !a->is_canonical)
return 0; /* A canonical connection is better than a non-canonical
@ -454,15 +463,26 @@ connection_or_is_better(const or_connection_t *a,
newer = b->_base.timestamp_created < a->_base.timestamp_created;
return
/* We prefer canonical connections regardless of newness. */
(!b->is_canonical && a->is_canonical) ||
/* If both have circuits we prefer the newer: */
(b->n_circuits && a->n_circuits && newer) ||
/* If neither has circuits we prefer the newer: */
(!b->n_circuits && !a->n_circuits && newer) ||
/* If only one has circuits, use that. */
(!b->n_circuits && a->n_circuits);
if (
/* We prefer canonical connections regardless of newness. */
(!b->is_canonical && a->is_canonical) ||
/* If both have circuits we prefer the newer: */
(b->n_circuits && a->n_circuits && newer) ||
/* If neither has circuits we prefer the newer: */
(!b->n_circuits && !a->n_circuits && newer))
return 1;
/* If one has no circuits and the other does... */
if (!b->n_circuits && a->n_circuits) {
/* Then it's bad, unless it's in its grace period and we're forgiving. */
if (forgive_new_connections &&
now < b->_base.timestamp_created + NEW_CONN_GRACE_PERIOD)
return 0;
else
return 1;
}
return 0;
}
/** Return the OR connection we should use to extend a circuit to the router
@ -480,6 +500,7 @@ connection_or_get_for_extend(const char *digest,
{
or_connection_t *conn, *best=NULL;
int n_inprogress_goodaddr = 0, n_old = 0, n_noncanonical = 0, n_possible = 0;
time_t now = approx_time();
tor_assert(msg_out);
tor_assert(launch_out);
@ -531,7 +552,7 @@ connection_or_get_for_extend(const char *digest,
continue;
}
if (connection_or_is_better(conn, best))
if (connection_or_is_better(now, conn, best, 0))
best = conn;
}
@ -619,7 +640,7 @@ connection_or_group_set_badness(or_connection_t *head)
continue;
}
if (!best || connection_or_is_better(or_conn, best))
if (!best || connection_or_is_better(now, or_conn, best, 0))
best = or_conn;
}
@ -645,7 +666,9 @@ connection_or_group_set_badness(or_connection_t *head)
or_conn->is_bad_for_new_circs ||
or_conn->_base.state != OR_CONN_STATE_OPEN)
continue;
if (or_conn != best) {
if (or_conn != best && connection_or_is_better(now, best, or_conn, 1)) {
/* This isn't the best conn, _and_ the best conn is better than it,
even when we're being forgiving. */
if (best->is_canonical) {
log_info(LD_OR,
"Marking OR conn to %s:%d as too old for new circuits: "