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Improvements to #11553 fix based on review

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Use a per-channel ratelim_t to control the rate at which we report
failures for each channel.

Explain why I picked N=32.

Never return a zero circID.

Thanks to Andrea and to cypherpunks.
This commit is contained in:
Nick Mathewson 2014-04-23 12:39:01 -04:00
parent 985deaaaf7
commit a770b74501
3 changed files with 20 additions and 8 deletions
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3
src/or/channel.c
View File

@ -731,6 +731,9 @@ channel_init(channel_t *chan)
/* Init timestamp */
chan->timestamp_last_added_nonpadding = time(NULL);
/* Warn about exhausted circuit IDs no more than hourly. */
chan->last_warned_circ_ids_exhausted.rate = 3600;
/* Initialize queues. */
TOR_SIMPLEQ_INIT(&chan->incoming_queue);
TOR_SIMPLEQ_INIT(&chan->outgoing_queue);

6
src/or/channel.h
View File

@ -148,8 +148,6 @@ struct channel_s {
ENUM_BF(circ_id_type_t) circ_id_type:2;
/** DOCDOC*/
unsigned wide_circ_ids:1;
/** Have we logged a warning about circID exhaustion on this channel? */
unsigned warned_circ_ids_exhausted:1;
/* For how many circuits are we n_chan? What about p_chan? */
unsigned int num_n_circuits, num_p_circuits;
@ -178,6 +176,10 @@ struct channel_s {
*/
unsigned int is_local:1;
/** Have we logged a warning about circID exhaustion on this channel?
* If so, when? */
ratelim_t last_warned_circ_ids_exhausted;
/** Channel timestamps for cell channels */
time_t timestamp_client; /* Client used this, according to relay.c */
time_t timestamp_drained; /* Output queue empty */

19
src/or/circuitbuild.c
View File

@ -102,6 +102,12 @@ channel_connect_for_circuit(const tor_addr_t *addr, uint16_t port,
static circid_t
get_unique_circ_id_by_chan(channel_t *chan)
{
/* This number is chosen somewhat arbitrarily; see comment below for more
* info. When the space is 80% full, it gives a one-in-a-million failure
* chance; when the space is 90% full, it gives a one-in-850 chance; and when
* the space is 95% full, it gives a one-in-26 failure chance. That seems
* okay, though you could make a case IMO for anything between N=32 and
* N=256. */
#define MAX_CIRCID_ATTEMPTS 64
circid_t test_circ_id;
@ -137,19 +143,20 @@ get_unique_circ_id_by_chan(channel_t *chan)
* whole circuit ID space every time we extend a circuit, which is
* not so great either.
*/
if (! chan->warned_circ_ids_exhausted) {
chan->warned_circ_ids_exhausted = 1;
log_warn(LD_CIRC,"No unused circIDs found on channel %s wide "
log_fn_ratelim(&chan->last_warned_circ_ids_exhausted, LOG_WARN,
LD_CIRC,"No unused circIDs found on channel %s wide "
"circID support, with %u inbound and %u outbound circuits. "
"Failing a circuit.",
chan->wide_circ_ids ? "with" : "without",
chan->num_p_circuits, chan->num_n_circuits);
}
return 0;
}
crypto_rand((char*) &test_circ_id, sizeof(test_circ_id));
test_circ_id &= mask;
do {
crypto_rand((char*) &test_circ_id, sizeof(test_circ_id));
test_circ_id &= mask;
} while (test_circ_id == 0);
test_circ_id |= high_bit;
} while (circuit_id_in_use_on_channel(test_circ_id, chan));
return test_circ_id;