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dos: Add extra safety asserts in cc_stats_refill_bucket()

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Never allow the function to set a bucket value above the allowed circuit
burst.

Closes #25202

Signed-off-by: David Goulet <dgoulet@torproject.org>
This commit is contained in:
David Goulet 2018-02-13 10:41:21 -05:00
parent 1555946e20
commit 305e39d0f8
2 changed files with 14 additions and 0 deletions
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4
changes/ticket25202 Normal file
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@ -0,0 +1,4 @@
o Minor bugfixes (DoS mitigation):
- Add extra safety checks when refilling the circuit creation bucket to
ensure we never set a value that is above the allowed burst. Fixes
ticket 25202.

10
src/or/dos.c
View File

@ -309,6 +309,16 @@ cc_stats_refill_bucket(cc_client_stats_t *stats, const tor_addr_t *addr)
new_circuit_bucket_count = MIN(stats->circuit_bucket + (uint32_t)num_token,
dos_cc_circuit_burst);
}
/* This function is not allowed to make the bucket count larger than the
* burst value */
tor_assert_nonfatal(new_circuit_bucket_count <= dos_cc_circuit_burst);
/* This function is not allowed to make the bucket count smaller, unless it
* is decreasing it to a newly configured, lower burst value. We allow the
* bucket to stay the same size, in case the circuit rate is zero. */
tor_assert_nonfatal(new_circuit_bucket_count >= stats->circuit_bucket ||
new_circuit_bucket_count == dos_cc_circuit_burst);
log_debug(LD_DOS, "DoS address %s has its circuit bucket value: %" PRIu32
". Filling it to %" PRIu32 ". Circuit rate is %" PRIu64
". Elapsed time is %" PRIi64,