commit c32ec9c425e9539bcc8ede95612e2d331c2cc2dd
Author: Roger Dingledine <arma(a)torproject.org>
Date: Thu Jun 28 14:00:01 2012 -0400
Detect bug 6252 (unexpected sendme cell)
I only check on circuits, not streams, since bloating your stream
window past the initial circuit window can't help you much.
Also, I compare to CIRCWINDOW_START_MAX so we don't have surprising
races if we lower CIRCWINDOW_START for an experiment.
---
changes/bug6252 | 8 ++++++++
src/or/relay.c | 14 ++++++++++++++
2 files changed, 22 insertions(+), 0 deletions(-)
diff --git a/changes/bug6252 b/changes/bug6252
new file mode 100644
index 0000000..0d29203
--- /dev/null
+++ b/changes/bug6252
@@ -0,0 +1,8 @@
+ o Security fixes:
+ - Tear down the circuit if we get an unexpected SENDME cell. Clients
+ could use this trick to make their circuits receive cells faster
+ than our flow control would have allowed, or to gum up the network,
+ or possibly to do targeted memory denial-of-service attacks on
+ entry nodes. Fixes bug 6252. Bugfix on the 54th commit on Tor --
+ from July 2002, before the release of Tor 0.0.0.
+
diff --git a/src/or/relay.c b/src/or/relay.c
index 3f894bf..4ab4403 100644
--- a/src/or/relay.c
+++ b/src/or/relay.c
@@ -1265,11 +1265,25 @@ connection_edge_process_relay_cell(cell_t *cell, circuit_t *circ,
case RELAY_COMMAND_SENDME:
if (!conn) {
if (layer_hint) {
+ if (layer_hint->package_window + CIRCWINDOW_INCREMENT >
+ CIRCWINDOW_START_MAX) {
+ log_fn(LOG_PROTOCOL_WARN, LD_PROTOCOL,
+ "Bug/attack: unexpected sendme cell from exit relay. "
+ "Closing circ.");
+ return -END_CIRC_REASON_TORPROTOCOL;
+ }
layer_hint->package_window += CIRCWINDOW_INCREMENT;
log_debug(LD_APP,"circ-level sendme at origin, packagewindow %d.",
layer_hint->package_window);
circuit_resume_edge_reading(circ, layer_hint);
} else {
+ if (circ->package_window + CIRCWINDOW_INCREMENT >
+ CIRCWINDOW_START_MAX) {
+ log_fn(LOG_PROTOCOL_WARN, LD_PROTOCOL,
+ "Bug/attack: unexpected sendme cell from client. "
+ "Closing circ.");
+ return -END_CIRC_REASON_TORPROTOCOL;
+ }
circ->package_window += CIRCWINDOW_INCREMENT;
log_debug(LD_APP,
"circ-level sendme at non-origin, packagewindow %d.",