Commit 93ac6ec4 authored by Roger Dingledine's avatar Roger Dingledine Committed by David Goulet
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exit: Deny re-entry into the network

Exit relays now reject exit attempts to known relay addresses + ORPort and
also to authorities on the ORPort and DirPort.

Closes #2667

Signed-off-by: David Goulet's avatarDavid Goulet <>
parent f26950fa
o Major feature (exit):
- Re-entry into the network is now denied at the Exit level to all relays'
ORPort and authorities' ORPort+DirPort. This is to help mitigate a series
of attacks. See ticket for more information. Closes ticket 2667.
......@@ -4035,6 +4035,31 @@ connection_exit_connect(edge_connection_t *edge_conn)
/* Next, check for attempts to connect back into the Tor network. We don't
* want to allow these for the same reason we don't want to allow
* infinite-length circuits (see "A Practical Congestion Attack on Tor Using
* Long Paths", Usenix Security 2009). See also ticket 2667.
* The TORPROTOCOL reason is used instead of EXITPOLICY so client do NOT
* attempt to retry connecting onto another circuit that will also fail
* bringing considerable more load on the network if so.
* Since the address+port set here is a bloomfilter, in very rare cases, the
* check will create a false positive meaning that the destination could
* actually be legit and thus being denied exit. However, sending back a
* reason that makes the client retry results in much worst consequences in
* case of an attack so this is a small price to pay. */
if (!connection_edge_is_rendezvous_stream(edge_conn) &&
nodelist_reentry_probably_contains(&conn->addr, conn->port)) {
log_info(LD_EXIT, "%s:%d tried to connect back to a known relay address. "
"Closing.", escaped_safe_str_client(conn->address),
connection_edge_end(edge_conn, END_STREAM_REASON_TORPROTOCOL);
circuit_detach_stream(circuit_get_by_edge_conn(edge_conn), edge_conn);
#ifdef HAVE_SYS_UN_H
if (conn->socket_family != AF_UNIX) {
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