Merge dashpay#6261: fix: assert in signing_shares for quorums with 3 members but 2 nodes only

f44edde tests: use only 2 MN and 2 Evo nodes in feature_asset_locks.py to be sure that is enough (Konstantin Akimov)
8286bdf fix: assert in signing_shares - amount of members can match with amount of attempts (Konstantin Akimov)

Pull request description:

  ## Issue being fixed or feature implemented
  Currently we have several quorums which have size 3 with threshold 2 nodes: `llmq_test_instantsend`, `llmq_test_platform`, `llmq_test` and they are used on RegTest.

  For extreme case when only 2 nodes exist the assert happens:

  ```
    AssertionError: Unexpected stderr dashd: llmq/signing_shares.cpp:812: static CDeterministicMNCPtr llmq::CSigSharesManager::SelectMemberForRecovery(const llmq::CQuorumCPtr&, const uint256&, size_t): Assertion `size_t(attempt) < quorum->members.size()' failed.
    Posix Signal: Aborted
       0#: (0x5BF40CE70DA2) stl_vector.h:115       - std::_Vector_base<unsigned long, std::allocator<unsigned long> >::_Vector_impl_data::_M_copy_data(std::_Vector_base<unsigned long, std::allocator<unsigned long> >::_Vector_impl_data const&)
       1#: (0x5BF40CE70DA2) stl_vector.h:127       - std::_Vector_base<unsigned long, std::allocator<unsigned long> >::_Vector_impl_data::_M_swap_data(std::_Vector_base<unsigned long, std::allocator<unsigned long> >::_Vector_impl_data&)
       2#: (0x5BF40CE70DA2) stl_vector.h:1962      - std::vector<unsigned long, std::allocator<unsigned long> >::_M_move_assign(std::vector<unsigned long, std::allocator<unsigned long> >&&, std::integral_constant<bool, true>)
       3#: (0x5BF40CE70DA2) stl_vector.h:771       - std::vector<unsigned long, std::allocator<unsigned long> >::operator=(std::vector<unsigned long, std::allocator<unsigned long> >&&)
       4#: (0x5BF40CE70DA2) stacktraces.cpp:777    - HandlePosixSignal
       5#: (0x7664C9245320) libc_sigaction.c       - ???
       6#: (0x7664C929EB1C) pthread_kill.c:44      - __pthread_kill_implementation
       7#: (0x7664C929EB1C) pthread_kill.c:78      - __pthread_kill_internal
       8#: (0x7664C929EB1C) pthread_kill.c:89      - __GI___pthread_kill
       9#: (0x7664C924526E) raise.c:27             - __GI_raise
      10#: (0x7664C92288FF) abort.c:81             - __GI_abort
      11#: (0x7664C922881B) loadmsgcat.c:1177      - _nl_load_domain
      12#: (0x7664C923B507) <unknown-file>         - ???
      13#: (0x5BF40C6E88C8) signing_shares.cpp:823 - llmq::CSigSharesManager::SelectMemberForRecovery(std::shared_ptr<llmq::CQuorum const> const&, uint256 const&, unsigned long)
      14#: (0x5BF40C94A285) quorums.cpp:737        - operator()
      15#: (0x5BF40C94A514) std_function.h:292     - _M_invoke
      16#: (0x5BF40CE082C6) util.cpp:510           - RPCHelpMan::HandleRequest(JSONRPCRequest const&) const
      17#: (0x5BF40C89824A) univalue.h:17          - UniValue::operator=(UniValue&&)
      18#: (0x5BF40C89824A) server.h:108           - CRPCCommand::CRPCCommand(std::__cxx11::basic_string<char, std::char_traits<char>, std::allocator<char> >, RPCHelpMan (*)())::{lambda(JSONRPCRequest const&, UniValue&, bool)#1}::operator()(JSONRPCRequest const&, UniValue&, bool) const
      19#: (0x5BF40C9976F4) std_function.h:591     - std::function<bool (JSONRPCRequest const&, UniValue&, bool)>::operator()(JSONRPCRequest const&, UniValue&, bool) const
      20#: (0x5BF40C9976F4) server.cpp:622         - ExecuteCommand
      21#: (0x5BF40C99879F) server.cpp:511         - ExecuteCommands
      22#: (0x5BF40C99879F) server.cpp:543         - CRPCTable::execute(JSONRPCRequest const&) const
      23#: (0x5BF40CB75F24) httprpc.cpp:247        - HTTPReq_JSONRPC
  ```

  Discovered during implementation of dashpay/dash-issues#77

  ## What was done?
  Changed condition in assert, implemented special case of using Nth element from array size N for `SelectMemberForRecovery`, added test for this case.

  ## How Has This Been Tested?
  Improved functional test `feature_asset_locks.py` to test this corner case for quorum `llmq_test_instantsend` and `llmq_test_platform`

  ## Breaking Changes
  N/A

  ## Checklist:
  - [x] I have performed a self-review of my own code
  - [x] I have commented my code, particularly in hard-to-understand areas
  - [x] I have added or updated relevant unit/integration/functional/e2e tests
  - [ ] I have made corresponding changes to the documentation
  - [x] I have assigned this pull request to a milestone

ACKs for top commit:
  UdjinM6:
    utACK f44edde
  PastaPastaPasta:
    utACK f44edde

Tree-SHA512: 5e8035960100778820bbbb242a8a354a27bce00c169bbebc4f3867737301dbdd3cc5993a8d806d55bf6eb467bfe1f36443087a271acc227ba7bb301c4f75bb7a

Author: PastaPastaPasta

src/llmq/signing_shares.cpp

@@ -807,9 +807,9 @@ void CSigSharesManager::TryRecoverSig(const CQuorumCPtr& quorum, const uint256&
     sigman.ProcessRecoveredSig(rs);
 }
 
-CDeterministicMNCPtr CSigSharesManager::SelectMemberForRecovery(const CQuorumCPtr& quorum, const uint256 &id, size_t attempt)
+CDeterministicMNCPtr CSigSharesManager::SelectMemberForRecovery(const CQuorumCPtr& quorum, const uint256 &id, int attempt)
 {
-    assert(size_t(attempt) < quorum->members.size());
+    assert(attempt < quorum->params.recoveryMembers);
 
     std::vector<std::pair<uint256, CDeterministicMNCPtr>> v;
     v.reserve(quorum->members.size());
@@ -819,7 +819,7 @@ CDeterministicMNCPtr CSigSharesManager::SelectMemberForRecovery(const CQuorumCPt
     }
     std::sort(v.begin(), v.end());
 
-    return v[attempt].second;
+    return v[attempt % v.size()].second;
 }
 
 void CSigSharesManager::CollectSigSharesToRequest(std::unordered_map<NodeId, std::unordered_map<uint256, CSigSharesInv, StaticSaltedHasher>>& sigSharesToRequest)

src/llmq/signing_shares.h

@@ -434,7 +434,7 @@ class CSigSharesManager : public CRecoveredSigsListener
 
     void HandleNewRecoveredSig(const CRecoveredSig& recoveredSig) override;
 
-    static CDeterministicMNCPtr SelectMemberForRecovery(const CQuorumCPtr& quorum, const uint256& id, size_t attempt);
+    static CDeterministicMNCPtr SelectMemberForRecovery(const CQuorumCPtr& quorum, const uint256& id, int attempt);
 
 private:
     // all of these return false when the currently processed message should be aborted (as each message actually contains multiple messages)

src/rpc/quorums.cpp

@@ -732,7 +732,7 @@ static RPCHelpMan quorum_selectquorum()
     ret.pushKV("quorumHash", quorum->qc->quorumHash.ToString());
 
     UniValue recoveryMembers(UniValue::VARR);
-    for (size_t i = 0; i < size_t(quorum->params.recoveryMembers); i++) {
+    for (int i = 0; i < quorum->params.recoveryMembers; ++i) {
         auto dmn = llmq_ctx.shareman->SelectMemberForRecovery(quorum, id, i);
         recoveryMembers.push_back(dmn->proTxHash.ToString());
     }

test/functional/feature_asset_locks.py

@@ -47,7 +47,7 @@
 
 class AssetLocksTest(DashTestFramework):
     def set_test_params(self):
-        self.set_dash_test_params(5, 3, [["-whitelist=127.0.0.1", "-llmqtestinstantsenddip0024=llmq_test_instantsend"]] * 5, evo_count=3)
+        self.set_dash_test_params(4, 2, [["-whitelist=127.0.0.1", "-llmqtestinstantsenddip0024=llmq_test_instantsend"]] * 4, evo_count=2)
 
     def skip_test_if_missing_module(self):
         self.skip_if_no_wallet()
@@ -229,6 +229,13 @@ def slowly_generate_batch(self, count):
             self.nodes[1].generate(batch)
             self.sync_all()
 
+    # This functional test intentionally setup only 2 MN and only 2 Evo nodes
+    # to ensure that corner case of quorum with minimum amount of nodes as possible
+    # does not cause any issues in Dash Core
+    def mine_quorum_2_nodes(self, llmq_type_name, llmq_type):
+        self.mine_quorum(llmq_type_name=llmq_type_name, expected_members=2, expected_connections=1, expected_contributions=2, expected_commitments=2, llmq_type=llmq_type)
+
+
     def run_test(self):
         node_wallet = self.nodes[0]
         node = self.nodes[1]
@@ -241,9 +248,9 @@ def run_test(self):
         self.nodes[0].sporkupdate("SPORK_2_INSTANTSEND_ENABLED", 0)
         self.wait_for_sporks_same()
 
-        self.mine_quorum(llmq_type_name='llmq_test_instantsend', llmq_type=104)
+        self.mine_quorum_2_nodes(llmq_type_name='llmq_test_instantsend', llmq_type=104)
 
-        for _ in range(3):
+        for _ in range(2):
             self.dynamically_add_masternode(evo=True)
             node.generate(8)
             self.sync_blocks()
@@ -321,7 +328,7 @@ def test_asset_locks(self, node_wallet, node, pubkey):
         self.create_and_check_block([extra_lock_tx], expected_error = 'bad-cbtx-assetlocked-amount')
 
         self.log.info("Mine a quorum...")
-        self.mine_quorum(llmq_type_name='llmq_test_platform', llmq_type=106, expected_connections=2, expected_members=3, expected_contributions=3, expected_complaints=0, expected_justifications=0, expected_commitments=3 )
+        self.mine_quorum_2_nodes(llmq_type_name='llmq_test_platform', llmq_type=106)
 
         self.validate_credit_pool_balance(locked_1)
 
@@ -407,7 +414,7 @@ def test_asset_unlocks(self, node_wallet, node, pubkey):
             reason = "double copy")
 
         self.log.info("Mining next quorum to check tx 'asset_unlock_tx_late' is still valid...")
-        self.mine_quorum(llmq_type_name="llmq_test_platform", llmq_type=106)
+        self.mine_quorum_2_nodes(llmq_type_name='llmq_test_platform', llmq_type=106)
         self.log.info("Checking credit pool amount is same...")
         self.validate_credit_pool_balance(locked - 1 * COIN)
         self.check_mempool_result(tx=asset_unlock_tx_late, result_expected={'allowed': True, 'fees': {'base': Decimal(str(tiny_amount / COIN))}})
@@ -427,7 +434,7 @@ def test_asset_unlocks(self, node_wallet, node, pubkey):
                 result_expected={'allowed': False, 'reject-reason' : 'bad-assetunlock-too-late'})
 
         self.log.info("Checking that two quorums later it is too late because quorum is not active...")
-        self.mine_quorum(llmq_type_name="llmq_test_platform", llmq_type=106)
+        self.mine_quorum_2_nodes(llmq_type_name='llmq_test_platform', llmq_type=106)
         self.log.info("Expecting new reject-reason...")
         self.check_mempool_result(tx=asset_unlock_tx_too_late,
                 result_expected={'allowed': False, 'reject-reason' : 'bad-assetunlock-not-active-quorum'})
@@ -504,7 +511,7 @@ def test_withdrawal_limits(self, node_wallet, node, pubkey):
 
         self.log.info("Fast forward to the next day to reset all current unlock limits...")
         self.slowly_generate_batch(blocks_in_one_day)
-        self.mine_quorum(llmq_type_name="llmq_test_platform", llmq_type=106)
+        self.mine_quorum_2_nodes(llmq_type_name='llmq_test_platform', llmq_type=106)
 
         total = self.get_credit_pool_balance()
         coins = node_wallet.listunspent()