hs_pow: faster hs_circuitmap lookup for rend in pow_worker_job_t

The worker job queue for hs_pow needs what's effectively a weak pointer
to two circuits, but there's not a generic mechanism for this in c-tor.
The previous approach of circuit_get_by_global_id() is straightforward
but not efficient. These global IDs are normally only used by the
control port protocol. To reduce the number of O(N) lookups we have over
the whole circuit list, we can use hs_circuitmap to look up the rend
circuit by its auth cookie.

Signed-off-by: Micah Elizabeth Scott <beth@torproject.org>

src/feature/hs/hs_client.c

@@ -797,7 +797,7 @@ consider_sending_introduce1(origin_circuit_t *intro_circ,
       /* send it to the client-side pow cpuworker for solving. */
       intro_circ->hs_currently_solving_pow = 1;
       if (hs_pow_queue_work(intro_circ->global_identifier,
-                            rend_circ->global_identifier,
+                            rend_circ->hs_ident->rendezvous_cookie,
                             &pow_inputs) != 0) {
         log_warn(LD_REND, "Failed to enqueue PoW request");
       }

src/feature/hs/hs_pow.c

@@ -16,6 +16,7 @@
 #include "ext/equix/include/equix.h"
 #include "feature/hs/hs_cache.h"
 #include "feature/hs/hs_descriptor.h"
+#include "feature/hs/hs_circuitmap.h"
 #include "feature/hs/hs_client.h"
 #include "feature/hs/hs_pow.h"
 #include "lib/crypt_ops/crypto_rand.h"
@@ -356,7 +357,7 @@ typedef struct pow_worker_job_t {
 
   /** State: we'll look these up to figure out how to proceed after. */
   uint32_t intro_circ_identifier;
-  uint32_t rend_circ_identifier;
+  uint8_t rend_circ_cookie[HS_REND_COOKIE_LEN];
 
   /** Output: The worker thread will malloc and write its answer here,
    * or set it to NULL if it produced no useful answer. */
@@ -411,11 +412,17 @@ pow_worker_replyfn(void *work_)
 
   pow_worker_job_t *job = work_;
 
-  // look up the circuits that we're going to use this pow in
+  /* Look up the circuits that we're going to use this pow in.
+   * There's room for improvement here. We already had a fast mapping to
+   * rend circuits from some kind of identifier that we can keep in a
+   * pow_worker_job_t, but we don't have that index for intro circs at this
+   * time. If the linear search in circuit_get_by_global_id() is ever a
+   * noticeable bottleneck we should add another map.
+   */
   origin_circuit_t *intro_circ =
     circuit_get_by_global_id(job->intro_circ_identifier);
   origin_circuit_t *rend_circ =
-    circuit_get_by_global_id(job->rend_circ_identifier);
+    hs_circuitmap_get_established_rend_circ_client_side(job->rend_circ_cookie);
 
   /* try to re-create desc and ip */
   const ed25519_public_key_t *service_identity_pk = NULL;
@@ -466,14 +473,17 @@ pow_worker_replyfn(void *work_)
  */
 int
 hs_pow_queue_work(uint32_t intro_circ_identifier,
-                  uint32_t rend_circ_identifier,
+                  const uint8_t *rend_circ_cookie,
                   const hs_pow_solver_inputs_t *pow_inputs)
 {
   tor_assert(in_main_thread());
+  tor_assert(rend_circ_cookie);
+  tor_assert(pow_inputs);
 
   pow_worker_job_t *job = tor_malloc_zero(sizeof(*job));
   job->intro_circ_identifier = intro_circ_identifier;
-  job->rend_circ_identifier = rend_circ_identifier;
+  memcpy(&job->rend_circ_cookie, rend_circ_cookie,
+         sizeof job->rend_circ_cookie);
   memcpy(&job->pow_inputs, pow_inputs, sizeof job->pow_inputs);
 
   workqueue_entry_t *work;

src/feature/hs/hs_pow.h

@@ -145,7 +145,7 @@ void hs_pow_remove_seed_from_cache(const uint8_t *seed_head);
 void hs_pow_free_service_state(hs_pow_service_state_t *state);
 
 int hs_pow_queue_work(uint32_t intro_circ_identifier,
-                      uint32_t rend_circ_identifier,
+                      const uint8_t *rend_circ_cookie,
                       const hs_pow_solver_inputs_t *pow_inputs);
 
 #else /* !defined(HAVE_MODULE_POW) */
@@ -183,11 +183,11 @@ hs_pow_free_service_state(hs_pow_service_state_t *state)
 
 static inline int
 hs_pow_queue_work(uint32_t intro_circ_identifier,
-                  uint32_t rend_circ_identifier,
+                  const uint8_t *rend_circ_cookie,
                   const hs_pow_solver_inputs_t *pow_inputs)
 {
   (void)intro_circ_identifier;
-  (void)rend_circ_identifier;
+  (void)rend_circ_cookie;
   (void)pow_inputs;
   return -1;
 }