commit 8dba8a088d7c1402831ab5a7211a4a347a60ff7a Author: George Kadianakis desnacked@riseup.net Date: Wed Apr 1 14:33:09 2015 +0100

Block multiple introductions on the same intro circuit. --- changes/bug15515 | 4 ++++ src/or/or.h | 3 +++ src/or/rendmid.c | 13 +++++++++++++ 3 files changed, 20 insertions(+)

diff --git a/changes/bug15515 b/changes/bug15515 new file mode 100644 index 0000000..dda7c2f --- /dev/null +++ b/changes/bug15515 @@ -0,0 +1,4 @@ + o Minor features (DoS-resistance): + - Make it harder for attackers to overwhelm hidden services with + introductions, by blocking multiple introduction requests on the + same circuit. Resolves ticket #15515. diff --git a/src/or/or.h b/src/or/or.h index 34f055c..4459957 100644 --- a/src/or/or.h +++ b/src/or/or.h @@ -3157,6 +3157,9 @@ typedef struct or_circuit_t { * to the specification? */ unsigned int remaining_relay_early_cells : 4;

+ /* We have already received an INTRODUCE1 cell on this circuit. */ + unsigned int already_received_introduce1 : 1; + /** True iff this circuit was made with a CREATE_FAST cell. */ unsigned int is_first_hop : 1;

diff --git a/src/or/rendmid.c b/src/or/rendmid.c index 1bd11f6..2f75ffb 100644 --- a/src/or/rendmid.c +++ b/src/or/rendmid.c @@ -149,6 +149,19 @@ rend_mid_introduce(or_circuit_t *circ, const uint8_t *request, goto err; }

+ /* We have already done an introduction on this circuit but we just + received a request for another one. We block it since this might + be an attempt to DoS a hidden service (#15515). */ + if (circ->already_received_introduce1) { + log_fn(LOG_PROTOCOL_WARN, LD_REND, + "Blocking multiple introductions on the same circuit. " + "Someone might be trying to attack a hidden service through " + "this relay."); + goto err; + } + + circ->already_received_introduce1 = 1; + /* We could change this to MAX_HEX_NICKNAME_LEN now that 0.0.9.x is * obsolete; however, there isn't much reason to do so, and we're going * to revise this protocol anyway.