commit 0187bd872885343761174218529aed7058f8d636
Author: Nick Mathewson <nickm(a)torproject.org>
Date: Fri Oct 28 10:51:21 2011 -0400
Implement the last of proposal 110
Reject all EXTEND requests not received in a relay_early cell
---
changes/prop110 | 7 +++++++
src/or/relay.c | 19 +++++++++++++++++++
2 files changed, 26 insertions(+), 0 deletions(-)
diff --git a/changes/prop110 b/changes/prop110
new file mode 100644
index 0000000..843595e
--- /dev/null
+++ b/changes/prop110
@@ -0,0 +1,7 @@
+ o Major features:
+ - Now that Tor 0.2.0.x is completely deprecated, we can enable the
+ final part of "Proposal 110: Avoiding infinite length circuits"
+ by refusing all circuit-extend requests that do not appear in a
+ "relay_early" cell. This change helps Tor to resist a class of
+ denial-of-service attacks by limiting the maximum circuit length.
+
diff --git a/src/or/relay.c b/src/or/relay.c
index 6cf4b73..60d439a 100644
--- a/src/or/relay.c
+++ b/src/or/relay.c
@@ -1194,6 +1194,25 @@ connection_edge_process_relay_cell(cell_t *cell, circuit_t *circ,
"'extend' cell received for non-zero stream. Dropping.");
return 0;
}
+ if (cell->command != CELL_RELAY_EARLY) {
+#define EARLY_WARNING_INTERVAL 900
+ static ratelim_t early_warning_limit =
+ RATELIM_INIT(EARLY_WARNING_INTERVAL);
+ char *m;
+ if (cell->command == CELL_RELAY) {
+ if ((m = rate_limit_log(&early_warning_limit, approx_time()))) {
+ /* XXXX make this a protocol_warn once we're happier with it*/
+ log_fn(LOG_WARN, domain, "EXTEND cell received, "
+ "but not via RELAY_EARLY. Dropping.%s", m);
+ tor_free(m);
+ }
+ } else {
+ log_fn(LOG_WARN, domain,
+ "EXTEND cell received, in a cell with type %d! Dropping.",
+ cell->command);
+ }
+ return 0;
+ }
return circuit_extend(cell, circ);
case RELAY_COMMAND_EXTENDED:
if (!layer_hint) {