hs-v3: Require reasonably live consensus

Some days before this commit, the network experienced a DDoS on the directory
authorities that prevented them to generate a consensus for more than 5 hours
straight.

That in turn entirely disabled onion service v3, client and service side, due
to the subsystem requiring a live consensus to function properly.

We know require a reasonably live consensus which means that the HSv3
subsystem will to its job for using the best consensus tor can find. If the
entire network is using an old consensus, than this should be alright.

If the service happens to use a live consensus while a client is not, it
should still work because the client will use the current SRV it sees which
might be the previous SRV for the service for which it still publish
descriptors for.

If the service is using an old one and somehow can't get a new one while
clients are on a new one, then reachability issues might arise. However, this
is a situation we already have at the moment since the service will simply not
work if it doesn't have a live consensus while a client has one.

Fixes #40237

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

1 files changed, 16 insertions, 7 deletions

diff --git a/src/feature/hs_common/shared_random_client.c b/src/feature/hs_common/shared_random_client.c
index 3d6be94080..ead5d681a9 100644
--- a/src/feature/hs_common/shared_random_client.c
+++ b/src/feature/hs_common/shared_random_client.c
@@ -13,6 +13,7 @@
 
 #include "app/config/config.h"
 #include "feature/dircommon/voting_schedule.h"
+#include "feature/nodelist/microdesc.h"
 #include "feature/nodelist/networkstatus.h"
 #include "lib/encoding/binascii.h"
 
@@ -37,7 +38,9 @@ int
 get_voting_interval(void)
 {
   int interval;
-  networkstatus_t *consensus = networkstatus_get_live_consensus(time(NULL));
+  networkstatus_t *consensus =
+    networkstatus_get_reasonably_live_consensus(time(NULL),
+                                                usable_consensus_flavor());
 
   if (consensus) {
     interval = (int)(consensus->fresh_until - consensus->valid_after);
@@ -142,7 +145,8 @@ sr_get_current(const networkstatus_t *ns)
   if (ns) {
     consensus = ns;
   } else {
-    consensus = networkstatus_get_live_consensus(approx_time());
+    consensus = networkstatus_get_reasonably_live_consensus(approx_time(),
+                                                  usable_consensus_flavor());
   }
   /* Ideally we would never be asked for an SRV without a live consensus. Make
    * sure this assumption is correct. */
@@ -165,7 +169,8 @@ sr_get_previous(const networkstatus_t *ns)
   if (ns) {
     consensus = ns;
   } else {
-    consensus = networkstatus_get_live_consensus(approx_time());
+    consensus = networkstatus_get_reasonably_live_consensus(approx_time(),
+                                                  usable_consensus_flavor());
   }
   /* Ideally we would never be asked for an SRV without a live consensus. Make
    * sure this assumption is correct. */
@@ -237,10 +242,14 @@ sr_state_get_start_time_of_current_protocol_run(void)
   int voting_interval = get_voting_interval();
   time_t beginning_of_curr_round;
 
-  /* This function is not used for voting purposes, so if we have a live
-     consensus, use its valid-after as the beginning of the current round,
-     otherwise resort to the voting schedule which should always exist. */
-  networkstatus_t *ns = networkstatus_get_live_consensus(approx_time());
+  /* This function is not used for voting purposes, so if we have a reasonably
+   * live consensus, use its valid-after as the beginning of the current
+   * round. If we have no consensus but we're an authority, use our own
+   * schedule. Otherwise, try using our view of the voting interval to figure
+   * out when the current round _should_ be starting. */
+  networkstatus_t *ns =
+    networkstatus_get_reasonably_live_consensus(approx_time(),
+                                                usable_consensus_flavor());
   if (ns) {
     beginning_of_curr_round = ns->valid_after;
   } else {