From 1ab6187071b78b05e443de9a33cb9be43e82f0d5 Mon Sep 17 00:00:00 2001
From: James Dorfman <dorfmanjames@gmail.com>
Date: Tue, 8 Oct 2024 04:50:58 +0000
Subject: [PATCH] Bug fix: when CheckChallenge(...) is called on a trimmed
 header, temporarily untrim it in order to extract the proof.

Without this fix, there would be an exception in this scenario, because a trimmed
header no longer has any proof information attached to it.

This scenario was occuring when a pre-dynafed node with trimmed blocks would receive
a new block header from its peer. The pre-dynafed node would try to validate the header
by comparing its proof to the previous block's proof, and this would cause an exception
if the previous block had pruned.

New headers are not pruned as soon as they're received. Rather, they are pruned whenever the block index
is flushed to disk. So, this behavior was only being observed in functional tests, when a pre-dynafed trimmed
node was restarted.
---
 src/block_proof.cpp | 11 +++++++++--
 src/block_proof.h   |  2 +-
 src/validation.cpp  |  3 ++-
 3 files changed, 12 insertions(+), 4 deletions(-)

diff --git a/src/block_proof.cpp b/src/block_proof.cpp
index 0c1a279d68..78a1765329 100644
--- a/src/block_proof.cpp
+++ b/src/block_proof.cpp
@@ -10,10 +10,17 @@
 #include <script/interpreter.h>
 #include <script/generic.hpp>
 
-bool CheckChallenge(const CBlockHeader& block, const CBlockIndex& indexLast, const Consensus::Params& params)
+bool CheckChallenge(const CBlockHeader& block, CBlockIndex& indexLast, const Consensus::Params& params)
 {
     if (g_signed_blocks) {
-        return block.proof.challenge == indexLast.get_proof().challenge;
+        if (indexLast.trimmed()) {
+            // Create a dummy block index to temporarily hold the untrimmed data
+            CBlockIndex tmp_index;
+            const CBlockIndex* pindexUntrimmed = indexLast.untrim_to(&tmp_index);
+            return block.proof.challenge == pindexUntrimmed->get_proof().challenge;
+        } else {
+            return block.proof.challenge == indexLast.get_proof().challenge;
+        }
     } else {
         return block.nBits == GetNextWorkRequired(&indexLast, &block, params);
     }
diff --git a/src/block_proof.h b/src/block_proof.h
index 273699f37f..9dbfb21ad8 100644
--- a/src/block_proof.h
+++ b/src/block_proof.h
@@ -20,6 +20,6 @@ class CScript;
 /** Check on header proof, depending on chain type, PoW or signed **/
 bool CheckProof(const CBlockHeader& block, const Consensus::Params&);
 bool CheckProofSignedParent(const CBlockHeader& block, const Consensus::Params&);
-bool CheckChallenge(const CBlockHeader& block, const CBlockIndex& indexLast, const Consensus::Params&);
+bool CheckChallenge(const CBlockHeader& block, CBlockIndex& indexLast, const Consensus::Params&);
 
 #endif // BITCOIN_BLOCK_PROOF_H
diff --git a/src/validation.cpp b/src/validation.cpp
index 53cf2cc0c2..11e9ce7884 100755
--- a/src/validation.cpp
+++ b/src/validation.cpp
@@ -3860,7 +3860,7 @@ static bool ContextualCheckDynaFedHeader(const CBlockHeader& block, BlockValidat
  *  in ConnectBlock().
  *  Note that -reindex-chainstate skips the validation that happens here!
  */
-static bool ContextualCheckBlockHeader(const CBlockHeader& block, BlockValidationState& state, BlockManager& blockman, const ChainstateManager& chainman, const CBlockIndex* pindexPrev, int64_t nAdjustedTime) EXCLUSIVE_LOCKS_REQUIRED(::cs_main)
+static bool ContextualCheckBlockHeader(const CBlockHeader& block, BlockValidationState& state, BlockManager& blockman, const ChainstateManager& chainman, CBlockIndex* pindexPrev, int64_t nAdjustedTime) EXCLUSIVE_LOCKS_REQUIRED(::cs_main)
 {
     AssertLockHeld(::cs_main);
     assert(pindexPrev != nullptr);
@@ -3868,6 +3868,7 @@ static bool ContextualCheckBlockHeader(const CBlockHeader& block, BlockValidatio
 
     // Check proof of work target or non-dynamic signblockscript if necessary
     const Consensus::Params& consensusParams = chainman.GetConsensus();
+
     if (!DeploymentActiveAfter(pindexPrev, chainman, Consensus::DEPLOYMENT_DYNA_FED) && !CheckChallenge(block, *pindexPrev, consensusParams))
         return state.Invalid(BlockValidationResult::BLOCK_INVALID_HEADER, "bad-diffbits", "incorrect proof of work");