Merge bitcoin/bitcoin#29509: [26.x] backports and final changes for v26.1rc2v26.1rc2

c68d4d0ac5b8537ba5e1c0c512b807768e1c5c1f [doc] update manual pages for v26.1rc2 (glozow)
bd715bfb3030f392b3b19f9a05aada48e385a0d9 [build] bump version to v26.1rc2 (glozow)
b6d006d2a2b840e4a5af96c8d838e1cf589d3bce update release notes 26.1 (glozow)
fce992b38e59c90babe505eda0d72f05d79eb2f3 fuzz: restrict fopencookie usage to Linux & FreeBSD (fanquake)
40c56a4d1341017b02dcb71882b1b1f03f880b1d test: make sure keypool sizes do not change on `getrawchangeaddress`/`getnewaddress` failures (UdjinM6)
7c82b2758c6bcfb8a94d2086f0d40088286815e8 wallet: Avoid updating `ReserveDestination::nIndex` when `GetReservedDestination` fails (UdjinM6)
b5419ce6b621121bb1a0ec497968eb16cc012c39 p2p: Don't consider blocks mutated if they don't connect to known prev block (Greg Sanders)
0535c253fe71ae9d875827cafed41a8889f4a702 [test] IsBlockMutated unit tests (dergoegge)
8141498f3ad3ae9c42c32346ee73dc7f29e72cb5 [validation] Cache merkle root and witness commitment checks (dergoegge)
0c5c5962cbfdfd532cebc6706d5b838488b89d53 [test] Add regression test for #27608 (dergoegge)
24736350e932799c66c999470fa3837e25576fc7 [net processing] Don't process mutated blocks (dergoegge)
50c0b61a9d562240d5fe4bd79324b0c0e79caa5c [validation] Merkle root malleation should be caught by IsBlockMutated (dergoegge)
aff368fa817b065d99729186d304fff02f6e527b [validation] Introduce IsBlockMutated (dergoegge)
076c67c3aae424e58863dde3bc37cedecc496935 [refactor] Cleanup merkle root checks (dergoegge)
97a1d0a45959a29464ae73087c7a0adcdebd5a61 [validation] Isolate merkle root checks (dergoegge)
4ac0eb543d028379bb2b86ab08bbbb2f9f48d5b1 test: Drop `x` modifier in `fsbridge::fopen` call for mingw builds (Hennadii Stepanov)

Pull request description:

  Includes:
  - #29357
  - #29412
  - #29524
  - #29510
  - #29529

  Also does:
  - update to release notes
  - bump to rc2
  - manpages
  - (no changes to bitcoin.conf)

ACKs for top commit:
  achow101:
    ACK c68d4d0ac5b8537ba5e1c0c512b807768e1c5c1f

Tree-SHA512: 2f8c3dd705e3f9f33403b3cc17e8006510ff827d7dbd609b09732a1669964e9b001cfecdc63d8d8daeb8f39c652e1e4ad0aac873d44d259c21803de85688ed2b

1 files changed, 116 insertions, 38 deletions

diff --git a/src/validation.cpp b/src/validation.cpp
index 5d435fef8b..f02d1e32a4 100644
--- a/src/validation.cpp
+++ b/src/validation.cpp
@@ -3621,6 +3621,87 @@ static bool CheckBlockHeader(const CBlockHeader& block, BlockValidationState& st
     return true;
 }
 
+static bool CheckMerkleRoot(const CBlock& block, BlockValidationState& state)
+{
+    if (block.m_checked_merkle_root) return true;
+
+    bool mutated;
+    uint256 merkle_root = BlockMerkleRoot(block, &mutated);
+    if (block.hashMerkleRoot != merkle_root) {
+        return state.Invalid(
+            /*result=*/BlockValidationResult::BLOCK_MUTATED,
+            /*reject_reason=*/"bad-txnmrklroot",
+            /*debug_message=*/"hashMerkleRoot mismatch");
+    }
+
+    // Check for merkle tree malleability (CVE-2012-2459): repeating sequences
+    // of transactions in a block without affecting the merkle root of a block,
+    // while still invalidating it.
+    if (mutated) {
+        return state.Invalid(
+            /*result=*/BlockValidationResult::BLOCK_MUTATED,
+            /*reject_reason=*/"bad-txns-duplicate",
+            /*debug_message=*/"duplicate transaction");
+    }
+
+    block.m_checked_merkle_root = true;
+    return true;
+}
+
+/** CheckWitnessMalleation performs checks for block malleation with regard to
+ * its witnesses.
+ *
+ * Note: If the witness commitment is expected (i.e. `expect_witness_commitment
+ * = true`), then the block is required to have at least one transaction and the
+ * first transaction needs to have at least one input. */
+static bool CheckWitnessMalleation(const CBlock& block, bool expect_witness_commitment, BlockValidationState& state)
+{
+    if (expect_witness_commitment) {
+        if (block.m_checked_witness_commitment) return true;
+
+        int commitpos = GetWitnessCommitmentIndex(block);
+        if (commitpos != NO_WITNESS_COMMITMENT) {
+            assert(!block.vtx.empty() && !block.vtx[0]->vin.empty());
+            const auto& witness_stack{block.vtx[0]->vin[0].scriptWitness.stack};
+
+            if (witness_stack.size() != 1 || witness_stack[0].size() != 32) {
+                return state.Invalid(
+                    /*result=*/BlockValidationResult::BLOCK_MUTATED,
+                    /*reject_reason=*/"bad-witness-nonce-size",
+                    /*debug_message=*/strprintf("%s : invalid witness reserved value size", __func__));
+            }
+
+            // The malleation check is ignored; as the transaction tree itself
+            // already does not permit it, it is impossible to trigger in the
+            // witness tree.
+            uint256 hash_witness = BlockWitnessMerkleRoot(block, /*mutated=*/nullptr);
+
+            CHash256().Write(hash_witness).Write(witness_stack[0]).Finalize(hash_witness);
+            if (memcmp(hash_witness.begin(), &block.vtx[0]->vout[commitpos].scriptPubKey[6], 32)) {
+                return state.Invalid(
+                    /*result=*/BlockValidationResult::BLOCK_MUTATED,
+                    /*reject_reason=*/"bad-witness-merkle-match",
+                    /*debug_message=*/strprintf("%s : witness merkle commitment mismatch", __func__));
+            }
+
+            block.m_checked_witness_commitment = true;
+            return true;
+        }
+    }
+
+    // No witness data is allowed in blocks that don't commit to witness data, as this would otherwise leave room for spam
+    for (const auto& tx : block.vtx) {
+        if (tx->HasWitness()) {
+            return state.Invalid(
+                /*result=*/BlockValidationResult::BLOCK_MUTATED,
+                /*reject_reason=*/"unexpected-witness",
+                /*debug_message=*/strprintf("%s : unexpected witness data found", __func__));
+        }
+    }
+
+    return true;
+}
+
 bool CheckBlock(const CBlock& block, BlockValidationState& state, const Consensus::Params& consensusParams, bool fCheckPOW, bool fCheckMerkleRoot)
 {
     // These are checks that are independent of context.
@@ -3639,17 +3720,8 @@ bool CheckBlock(const CBlock& block, BlockValidationState& state, const Consensu
     }
 
     // Check the merkle root.
-    if (fCheckMerkleRoot) {
-        bool mutated;
-        uint256 hashMerkleRoot2 = BlockMerkleRoot(block, &mutated);
-        if (block.hashMerkleRoot != hashMerkleRoot2)
-            return state.Invalid(BlockValidationResult::BLOCK_MUTATED, "bad-txnmrklroot", "hashMerkleRoot mismatch");
-
-        // Check for merkle tree malleability (CVE-2012-2459): repeating sequences
-        // of transactions in a block without affecting the merkle root of a block,
-        // while still invalidating it.
-        if (mutated)
-            return state.Invalid(BlockValidationResult::BLOCK_MUTATED, "bad-txns-duplicate", "duplicate transaction");
+    if (fCheckMerkleRoot && !CheckMerkleRoot(block, state)) {
+        return false;
     }
 
     // All potential-corruption validation must be done before we do any
@@ -3740,6 +3812,37 @@ bool HasValidProofOfWork(const std::vector<CBlockHeader>& headers, const Consens
             [&](const auto& header) { return CheckProofOfWork(header.GetHash(), header.nBits, consensusParams);});
 }
 
+bool IsBlockMutated(const CBlock& block, bool check_witness_root)
+{
+    BlockValidationState state;
+    if (!CheckMerkleRoot(block, state)) {
+        LogPrint(BCLog::VALIDATION, "Block mutated: %s\n", state.ToString());
+        return true;
+    }
+
+    if (block.vtx.empty() || !block.vtx[0]->IsCoinBase()) {
+        // Consider the block mutated if any transaction is 64 bytes in size (see 3.1
+        // in "Weaknesses in Bitcoin’s Merkle Root Construction":
+        // https://lists.linuxfoundation.org/pipermail/bitcoin-dev/attachments/20190225/a27d8837/attachment-0001.pdf).
+        //
+        // Note: This is not a consensus change as this only applies to blocks that
+        // don't have a coinbase transaction and would therefore already be invalid.
+        return std::any_of(block.vtx.begin(), block.vtx.end(),
+                           [](auto& tx) { return ::GetSerializeSize(tx, PROTOCOL_VERSION | SERIALIZE_TRANSACTION_NO_WITNESS) == 64; });
+    } else {
+        // Theoretically it is still possible for a block with a 64 byte
+        // coinbase transaction to be mutated but we neglect that possibility
+        // here as it requires at least 224 bits of work.
+    }
+
+    if (!CheckWitnessMalleation(block, check_witness_root, state)) {
+        LogPrint(BCLog::VALIDATION, "Block mutated: %s\n", state.ToString());
+        return true;
+    }
+
+    return false;
+}
+
 arith_uint256 CalculateHeadersWork(const std::vector<CBlockHeader>& headers)
 {
     arith_uint256 total_work{0};
@@ -3848,33 +3951,8 @@ static bool ContextualCheckBlock(const CBlock& block, BlockValidationState& stat
     // * There must be at least one output whose scriptPubKey is a single 36-byte push, the first 4 bytes of which are
     //   {0xaa, 0x21, 0xa9, 0xed}, and the following 32 bytes are SHA256^2(witness root, witness reserved value). In case there are
     //   multiple, the last one is used.
-    bool fHaveWitness = false;
-    if (DeploymentActiveAfter(pindexPrev, chainman, Consensus::DEPLOYMENT_SEGWIT)) {
-        int commitpos = GetWitnessCommitmentIndex(block);
-        if (commitpos != NO_WITNESS_COMMITMENT) {
-            bool malleated = false;
-            uint256 hashWitness = BlockWitnessMerkleRoot(block, &malleated);
-            // The malleation check is ignored; as the transaction tree itself
-            // already does not permit it, it is impossible to trigger in the
-            // witness tree.
-            if (block.vtx[0]->vin[0].scriptWitness.stack.size() != 1 || block.vtx[0]->vin[0].scriptWitness.stack[0].size() != 32) {
-                return state.Invalid(BlockValidationResult::BLOCK_MUTATED, "bad-witness-nonce-size", strprintf("%s : invalid witness reserved value size", __func__));
-            }
-            CHash256().Write(hashWitness).Write(block.vtx[0]->vin[0].scriptWitness.stack[0]).Finalize(hashWitness);
-            if (memcmp(hashWitness.begin(), &block.vtx[0]->vout[commitpos].scriptPubKey[6], 32)) {
-                return state.Invalid(BlockValidationResult::BLOCK_MUTATED, "bad-witness-merkle-match", strprintf("%s : witness merkle commitment mismatch", __func__));
-            }
-            fHaveWitness = true;
-        }
-    }
-
-    // No witness data is allowed in blocks that don't commit to witness data, as this would otherwise leave room for spam
-    if (!fHaveWitness) {
-      for (const auto& tx : block.vtx) {
-            if (tx->HasWitness()) {
-                return state.Invalid(BlockValidationResult::BLOCK_MUTATED, "unexpected-witness", strprintf("%s : unexpected witness data found", __func__));
-            }
-        }
+    if (!CheckWitnessMalleation(block, DeploymentActiveAfter(pindexPrev, chainman, Consensus::DEPLOYMENT_SEGWIT), state)) {
+        return false;
     }
 
     // After the coinbase witness reserved value and commitment are verified,