0004-patch-3-gin_check_posting_tree_parent_keys_consisten.patch

From cb6f5b84e3bf5f5716c5470ffb4823563b23d21f Mon Sep 17 00:00:00 2001
From: Arseniy Mukhin <arseniy.mukhin.dev@gmail.com>
Date: Mon, 9 Jun 2025 20:49:11 +0300
Subject: [PATCH 4/5] patch 3: gin_check_posting_tree_parent_keys_consistency

This commit address issues with parent_key checks for the posting tree in gin_index_check():
- Check if parentkey is valid before using it in the comparison. Checking that stack->parentblk is valid blocknum is not enough
- Set invalid parentkey for the rightmost child only, not for all children of the rightmost page.
---
 contrib/amcheck/t/006_verify_gin.pl | 40 +++++++++++++++++++++++++++++
 contrib/amcheck/verify_gin.c        | 12 +++------
 2 files changed, 44 insertions(+), 8 deletions(-)

diff --git a/contrib/amcheck/t/006_verify_gin.pl b/contrib/amcheck/t/006_verify_gin.pl
index fa6baa51546..a7c7c1f5a61 100644
--- a/contrib/amcheck/t/006_verify_gin.pl
+++ b/contrib/amcheck/t/006_verify_gin.pl
@@ -33,6 +33,7 @@ invalid_entry_order_inner_page_test();
 invalid_entry_columns_order_test();
 inconsistent_with_parent_key__parent_key_corrupted_test();
 inconsistent_with_parent_key__child_key_corrupted_test();
+inconsistent_with_parent_key__parent_key_corrupted_posting_tree_test();
 
 sub invalid_entry_order_leaf_page_test
 {
@@ -241,6 +242,45 @@ sub inconsistent_with_parent_key__child_key_corrupted_test
 	like($stderr, qr/$expected/);
 }
 
+sub inconsistent_with_parent_key__parent_key_corrupted_posting_tree_test
+{
+	my $relname = "test";
+	my $indexname = "test_gin_idx";
+
+	$node->safe_psql(
+		'postgres', qq(
+		DROP TABLE IF EXISTS $relname;
+		CREATE TABLE $relname (a text[]);
+		INSERT INTO $relname (a) select ('{aaaaa}') from generate_series(1,10000);
+		CREATE INDEX $indexname ON $relname USING gin (a);
+	));
+	my $relpath = relation_filepath($indexname);
+
+	$node->stop;
+
+	my $blkno = 2;  # posting tree root
+
+	# we have a posting tree for 'aaaaa' key with the root at 2nd block
+	# and two leaf pages 3 and 4. replace 4th page's high key with (1,1)
+	# so that there are tid's in leaf page that are larger then the new high key.
+	my $find = pack('S*', 0, 4, 0) . '....';
+	my $replace = pack('S*', 0, 4, 0, 1, 1);
+	string_replace_block(
+		$relpath,
+		$find,
+		$replace,
+		$blksize,
+		$blkno
+	);
+
+	$node->start;
+
+	my ($result, $stdout, $stderr) = $node->psql('postgres', qq(SELECT gin_index_check('$indexname')));
+	my $expected = "index \"$indexname\": tid exceeds parent's high key in postingTree leaf on block 4";
+	like($stderr, qr/$expected/);
+}
+
+
 # Returns the filesystem path for the named relation.
 sub relation_filepath
 {
diff --git a/contrib/amcheck/verify_gin.c b/contrib/amcheck/verify_gin.c
index 8f6a5410cb7..427cf1669a6 100644
--- a/contrib/amcheck/verify_gin.c
+++ b/contrib/amcheck/verify_gin.c
@@ -346,7 +346,7 @@ gin_check_posting_tree_parent_keys_consistency(Relation rel, BlockNumber posting
 				 * Check if this tuple is consistent with the downlink in the
 				 * parent.
 				 */
-				if (stack->parentblk != InvalidBlockNumber && i == maxoff &&
+				if (i == maxoff && ItemPointerIsValid(&stack->parentkey) &&
 					ItemPointerCompare(&stack->parentkey, &posting_item->key) < 0)
 					ereport(ERROR,
 							(errcode(ERRCODE_INDEX_CORRUPTED),
@@ -359,14 +359,10 @@ gin_check_posting_tree_parent_keys_consistency(Relation rel, BlockNumber posting
 				ptr->depth = stack->depth + 1;
 
 				/*
-				 * Set rightmost parent key to invalid item pointer. Its value
-				 * is 'Infinity' and not explicitly stored.
+				 * The rightmost parent key is always invalid item pointer.
+				 * Its value is 'Infinity' and not explicitly stored.
 				 */
-				if (rightlink == InvalidBlockNumber)
-					ItemPointerSetInvalid(&ptr->parentkey);
-				else
-					ptr->parentkey = posting_item->key;
-
+				ptr->parentkey = posting_item->key;
 				ptr->parentblk = stack->blkno;
 				ptr->blkno = BlockIdGetBlockNumber(&posting_item->child_blkno);
 				ptr->next = stack->next;
-- 
2.43.0