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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 <dgoulet@torproject.org>
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changes/ticket2667
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o Major feature (exit):
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- Re-entry into the network is now denied at the Exit level to all relays'
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ORPort and authorities' ORPort+DirPort. This is to help mitigate a series
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of attacks. See ticket for more information. Closes ticket 2667.
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@ -4263,6 +4263,30 @@ connection_exit_connect(edge_connection_t *edge_conn)
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return;
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}
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/* Next, check for attempts to connect back into the Tor network. We don't
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* want to allow these for the same reason we don't want to allow
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* infinite-length circuits (see "A Practical Congestion Attack on Tor Using
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* Long Paths", Usenix Security 2009). See also ticket 2667.
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*
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* The TORPROTOCOL reason is used instead of EXITPOLICY so client do NOT
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* attempt to retry connecting onto another circuit that will also fail
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* bringing considerable more load on the network if so.
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*
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* Since the address+port set here is a bloomfilter, in very rare cases, the
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* check will create a false positive meaning that the destination could
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* actually be legit and thus being denied exit. However, sending back a
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* reason that makes the client retry results in much worst consequences in
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* case of an attack so this is a small price to pay. */
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if (!connection_edge_is_rendezvous_stream(edge_conn) &&
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nodelist_reentry_probably_contains(&conn->addr, conn->port)) {
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log_info(LD_EXIT, "%s tried to connect back to a known relay address. "
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"Closing.", connection_describe(conn));
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connection_edge_end(edge_conn, END_STREAM_REASON_TORPROTOCOL);
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circuit_detach_stream(circuit_get_by_edge_conn(edge_conn), edge_conn);
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connection_free(conn);
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return;
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}
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#ifdef HAVE_SYS_UN_H
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if (conn->socket_family != AF_UNIX) {
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#else
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