From 99d5b835461c5689843efb8508035855a53ed43d Mon Sep 17 00:00:00 2001
From: PiRK <pierrekn@gmail.com>
Date: Mon, 23 Jan 2023 16:08:15 +0100
Subject: [PATCH] Require CBlockIndex::GetUndoPos() to hold mutex cs_main

Summary:
This is a partial backport of [[https://github.com/bitcoin/bitcoin/pull/22932 | core#22932]]
https://github.com/bitcoin/bitcoin/pull/22932/commits/572393448b4d32f91b92edc84b4200ab52d62422

Depends on D13032

Test Plan:
With clang and DEBUG:

`ninja all check-all`

Reviewers: #bitcoin_abc, Fabien

Reviewed By: #bitcoin_abc, Fabien

Differential Revision: https://reviews.bitcoinabc.org/D13033
---
 src/blockindex.h          | 3 ++-
 src/node/blockstorage.cpp | 3 ++-
 2 files changed, 4 insertions(+), 2 deletions(-)

diff --git a/src/blockindex.h b/src/blockindex.h
index a774a40375..04163d8c69 100644
--- a/src/blockindex.h
+++ b/src/blockindex.h
@@ -121,7 +121,8 @@ class CBlockIndex {
         return ret;
     }
 
-    FlatFilePos GetUndoPos() const {
+    FlatFilePos GetUndoPos() const EXCLUSIVE_LOCKS_REQUIRED(::cs_main) {
+        AssertLockHeld(::cs_main);
         FlatFilePos ret;
         if (nStatus.hasUndo()) {
             ret.nFile = nFile;
diff --git a/src/node/blockstorage.cpp b/src/node/blockstorage.cpp
index 3b49382563..df52066e4f 100644
--- a/src/node/blockstorage.cpp
+++ b/src/node/blockstorage.cpp
@@ -480,7 +480,8 @@ static bool UndoWriteToDisk(const CBlockUndo &blockundo, FlatFilePos &pos,
 }
 
 bool UndoReadFromDisk(CBlockUndo &blockundo, const CBlockIndex *pindex) {
-    FlatFilePos pos = pindex->GetUndoPos();
+    const FlatFilePos pos{WITH_LOCK(::cs_main, return pindex->GetUndoPos())};
+
     if (pos.IsNull()) {
         return error("%s: no undo data available", __func__);
     }