Mercurial > dovecot > core-2.2
changeset 21954:1c952a42bf12
auth: Shuffle failed auth requests before sending the failure replies.
This might be helpful against some timing attacks.
Using Fisher–Yates shuffle.
| author | Timo Sirainen <timo.sirainen@dovecot.fi> |
|---|---|
| date | Sun, 09 Apr 2017 15:31:11 +0300 |
| parents | ec6539bd0690 |
| children | 64d17b868bcc |
| files | src/auth/auth-request-handler.c |
| diffstat | 1 files changed, 21 insertions(+), 2 deletions(-) [+] |
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--- a/src/auth/auth-request-handler.c Sun Apr 09 15:19:25 2017 +0300 +++ b/src/auth/auth-request-handler.c Sun Apr 09 15:31:11 2017 +0300 @@ -805,7 +805,7 @@ void auth_request_handler_flush_failures(bool flush_all) { struct auth_request **auth_requests, *auth_request; - unsigned int i, count; + unsigned int i, j, count; time_t diff; count = aqueue_count(auth_failures); @@ -816,15 +816,34 @@ } auth_requests = array_idx_modifiable(&auth_failures_arr, 0); + /* count the number of requests that we need to flush */ for (i = 0; i < count; i++) { - auth_request = auth_requests[aqueue_idx(auth_failures, 0)]; + auth_request = auth_requests[aqueue_idx(auth_failures, i)]; /* FIXME: assumess that failure_delay is always the same. */ diff = ioloop_time - auth_request->last_access; if (diff < (time_t)auth_request->set->failure_delay && !flush_all) break; + } + /* shuffle these requests to try to prevent any kind of timing attacks + where attacker performs multiple requests in parallel and attempts + to figure out results based on the order of replies. */ + count = i; + for (i = 0; i < count; i++) { + j = random() % (count - i) + i; + auth_request = auth_requests[aqueue_idx(auth_failures, i)]; + + /* swap i & j */ + auth_requests[aqueue_idx(auth_failures, i)] = + auth_requests[aqueue_idx(auth_failures, j)]; + auth_requests[aqueue_idx(auth_failures, j)] = auth_request; + } + + /* flush the requests */ + for (i = 0; i < count; i++) { + auth_request = auth_requests[aqueue_idx(auth_failures, i)]; aqueue_delete_tail(auth_failures); i_assert(auth_request->state == AUTH_REQUEST_STATE_FINISHED);