Sanity assert GetAncestor() != nullptr where appropriate

Add sanity asserts for return value of `CBlockIndex::GetAncestor()` where appropriate.

In validation.cpp `CheckSequenceLocks`, check the return value of `tip->GetAncestor(maxInputHeight)` stored into `lp->maxInputBlock`. If it ever returns `nullptr` because the ancestor isn't found, it's going to be a bad bug to keep going, since a `LockPoints` object with the `maxInputBlock` member set to `nullptr` signifies no relative lock time.

In the other places, the added asserts would prevent accidental dereferencing of a null pointer which is undefined behavior.

Co-Authored-By: Aurèle Oulès <aurele@oules.com>
Co-Authored-By: danra <danra@users.noreply.github.com>

1 files changed, 11 insertions, 12 deletions

diff --git a/src/rpc/blockchain.cpp b/src/rpc/blockchain.cpp
index d6a6bd5f31..e3e988d473 100644
--- a/src/rpc/blockchain.cpp
+++ b/src/rpc/blockchain.cpp
@@ -1618,9 +1618,9 @@ static RPCHelpMan getchaintxstats()
         }
     }
 
-    const CBlockIndex* pindexPast = pindex->GetAncestor(pindex->nHeight - blockcount);
-    int nTimeDiff = pindex->GetMedianTimePast() - pindexPast->GetMedianTimePast();
-    int nTxDiff = pindex->nChainTx - pindexPast->nChainTx;
+    const CBlockIndex& past_block{*CHECK_NONFATAL(pindex->GetAncestor(pindex->nHeight - blockcount))};
+    const int64_t nTimeDiff{pindex->GetMedianTimePast() - past_block.GetMedianTimePast()};
+    const int nTxDiff = pindex->nChainTx - past_block.nChainTx;
 
     UniValue ret(UniValue::VOBJ);
     ret.pushKV("time", (int64_t)pindex->nTime);
@@ -1761,8 +1761,7 @@ static RPCHelpMan getblockstats()
 {
     ChainstateManager& chainman = EnsureAnyChainman(request.context);
     LOCK(cs_main);
-    const CBlockIndex* pindex{ParseHashOrHeight(request.params[0], chainman)};
-    CHECK_NONFATAL(pindex != nullptr);
+    const CBlockIndex& pindex{*CHECK_NONFATAL(ParseHashOrHeight(request.params[0], chainman))};
 
     std::set<std::string> stats;
     if (!request.params[1].isNull()) {
@@ -1773,8 +1772,8 @@ static RPCHelpMan getblockstats()
         }
     }
 
-    const CBlock block = GetBlockChecked(chainman.m_blockman, pindex);
-    const CBlockUndo blockUndo = GetUndoChecked(chainman.m_blockman, pindex);
+    const CBlock& block = GetBlockChecked(chainman.m_blockman, &pindex);
+    const CBlockUndo& blockUndo = GetUndoChecked(chainman.m_blockman, &pindex);
 
     const bool do_all = stats.size() == 0; // Calculate everything if nothing selected (default)
     const bool do_mediantxsize = do_all || stats.count("mediantxsize") != 0;
@@ -1892,25 +1891,25 @@ static RPCHelpMan getblockstats()
     ret_all.pushKV("avgfee", (block.vtx.size() > 1) ? totalfee / (block.vtx.size() - 1) : 0);
     ret_all.pushKV("avgfeerate", total_weight ? (totalfee * WITNESS_SCALE_FACTOR) / total_weight : 0); // Unit: sat/vbyte
     ret_all.pushKV("avgtxsize", (block.vtx.size() > 1) ? total_size / (block.vtx.size() - 1) : 0);
-    ret_all.pushKV("blockhash", pindex->GetBlockHash().GetHex());
+    ret_all.pushKV("blockhash", pindex.GetBlockHash().GetHex());
     ret_all.pushKV("feerate_percentiles", feerates_res);
-    ret_all.pushKV("height", (int64_t)pindex->nHeight);
+    ret_all.pushKV("height", (int64_t)pindex.nHeight);
     ret_all.pushKV("ins", inputs);
     ret_all.pushKV("maxfee", maxfee);
     ret_all.pushKV("maxfeerate", maxfeerate);
     ret_all.pushKV("maxtxsize", maxtxsize);
     ret_all.pushKV("medianfee", CalculateTruncatedMedian(fee_array));
-    ret_all.pushKV("mediantime", pindex->GetMedianTimePast());
+    ret_all.pushKV("mediantime", pindex.GetMedianTimePast());
     ret_all.pushKV("mediantxsize", CalculateTruncatedMedian(txsize_array));
     ret_all.pushKV("minfee", (minfee == MAX_MONEY) ? 0 : minfee);
     ret_all.pushKV("minfeerate", (minfeerate == MAX_MONEY) ? 0 : minfeerate);
     ret_all.pushKV("mintxsize", mintxsize == MAX_BLOCK_SERIALIZED_SIZE ? 0 : mintxsize);
     ret_all.pushKV("outs", outputs);
-    ret_all.pushKV("subsidy", GetBlockSubsidy(pindex->nHeight, Params().GetConsensus()));
+    ret_all.pushKV("subsidy", GetBlockSubsidy(pindex.nHeight, Params().GetConsensus()));
     ret_all.pushKV("swtotal_size", swtotal_size);
     ret_all.pushKV("swtotal_weight", swtotal_weight);
     ret_all.pushKV("swtxs", swtxs);
-    ret_all.pushKV("time", pindex->GetBlockTime());
+    ret_all.pushKV("time", pindex.GetBlockTime());
     ret_all.pushKV("total_out", total_out);
     ret_all.pushKV("total_size", total_size);
     ret_all.pushKV("total_weight", total_weight);