hs: Limit the amount of relayed INTRODUCE2

This commit add the hs_dos.{c|h} file that has the purpose of having the
anti-DoS code for onion services.

At this commit, it only has one which is a function that decides if an
INTRODUCE2 can be sent on the given introduction service circuit (S<->IP)
using a simple token bucket.

The rate per second is 25 and allowed burst to 200.

Basic defenses on #15516.

Signed-off-by: David Goulet <dgoulet@torproject.org>

1 files changed, 7 insertions, 0 deletions

diff --git a/src/core/or/or_circuit_st.h b/src/core/or/or_circuit_st.h
index 6789668224..8f319585a6 100644
--- a/src/core/or/or_circuit_st.h
+++ b/src/core/or/or_circuit_st.h
@@ -12,6 +12,8 @@
 #include "core/or/circuit_st.h"
 #include "core/or/crypt_path_st.h"
 
+#include "lib/evloop/token_bucket.h"
+
 struct onion_queue_t;
 
 /** An or_circuit_t holds information needed to implement a circuit at an
@@ -69,6 +71,11 @@ struct or_circuit_t {
    * exit-ward queues of this circuit; reset every time when writing
    * buffer stats to disk. */
   uint64_t total_cell_waiting_time;
+
+  /** INTRODUCE2 cell bucket controlling how much can go on this circuit. Only
+   * used if this is a service introduction circuit at the intro point
+   * (purpose = CIRCUIT_PURPOSE_INTRO_POINT). */
+  token_bucket_ctr_t introduce2_bucket;
 };
 
 #endif /* !defined(OR_CIRCUIT_ST_H) */