From c99667583dd9b57612edf4c04611cd4857250600 Mon Sep 17 00:00:00 2001
From: stratospher <44024636+stratospher@users.noreply.github.com>
Date: Fri, 7 Feb 2025 09:29:31 +0530
Subject: [PATCH] validation: fix traversal condition to mark
 BLOCK_FAILED_CHILD
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this block of code is not reached on master since other than
initialisation, all other iterations have invalid_walk_tip
and to_mark_failed pointers in some form of this layout
where 1, 2, 3 and 4 are block heights.

	invalid_walk_tip
	  ↓
1 <- 2 <- 3 <- 4
	       ↑
	      to_mark_failed

fix it so that blocks are correctly marked as BLOCK_FAILED_CHILD
if it's a descendant of BLOCK_FAILED_VALID block.
---
 src/validation.cpp | 2 +-
 1 file changed, 1 insertion(+), 1 deletion(-)

diff --git a/src/validation.cpp b/src/validation.cpp
index 0384018bc36..673c9272fe6 100644
--- a/src/validation.cpp
+++ b/src/validation.cpp
@@ -3747,7 +3747,7 @@ bool Chainstate::InvalidateBlock(BlockValidationState& state, CBlockIndex* pinde
         m_blockman.m_dirty_blockindex.insert(invalid_walk_tip);
         setBlockIndexCandidates.erase(invalid_walk_tip);
         setBlockIndexCandidates.insert(invalid_walk_tip->pprev);
-        if (invalid_walk_tip->pprev == to_mark_failed && (to_mark_failed->nStatus & BLOCK_FAILED_VALID)) {
+        if (invalid_walk_tip == to_mark_failed->pprev && (to_mark_failed->nStatus & BLOCK_FAILED_VALID)) {
             // We only want to mark the last disconnected block as BLOCK_FAILED_VALID; its children
             // need to be BLOCK_FAILED_CHILD instead.
             to_mark_failed->nStatus = (to_mark_failed->nStatus ^ BLOCK_FAILED_VALID) | BLOCK_FAILED_CHILD;