From 6c26ede8edcb700caca12c501c6c129801989526 Mon Sep 17 00:00:00 2001
From: Mark Andrews <marka@isc.org>
Date: Fri, 23 Feb 2024 10:12:47 +1100
Subject: [PATCH] Do not use header_prev in expire_lru_headers

dns__cacherbt_expireheader can unlink / free header_prev underneath
it.  Use ISC_LIST_TAIL after calling dns__cacherbt_expireheader
instead to get the next pointer to be processed.

(cherry picked from commit 7ce2e86024f022decb2678963538515ca39ab4ab)
(cherry picked from commit f88f21b7d890eb80097f4bd434fedb29c2f9ff63)
---
 lib/dns/rbtdb.c | 8 ++++----
 1 file changed, 4 insertions(+), 4 deletions(-)

diff --git a/lib/dns/rbtdb.c b/lib/dns/rbtdb.c
index e61cb21..4171039 100644
--- a/lib/dns/rbtdb.c
+++ b/lib/dns/rbtdb.c
@@ -10358,19 +10358,19 @@ update_header(dns_rbtdb_t *rbtdb, rdatasetheader_t *header,
 static size_t
 expire_lru_headers(dns_rbtdb_t *rbtdb, unsigned int locknum, size_t purgesize,
 		   isc_boolean_t tree_locked) {
-	rdatasetheader_t *header, *header_prev;
+	rdatasetheader_t *header;
 	size_t purged = 0;
 
 	for (header = ISC_LIST_TAIL(rbtdb->rdatasets[locknum]);
-	     header != NULL && purged <= purgesize; header = header_prev)
+	     header != NULL && purged <= purgesize;
+	     header = ISC_LIST_TAIL(rbtdb->rdatasets[locknum]))
 	{
-		header_prev = ISC_LIST_PREV(header, link);
 		/*
 		 * Unlink the entry at this point to avoid checking it
 		 * again even if it's currently used someone else and
 		 * cannot be purged at this moment.  This entry won't be
 		 * referenced any more (so unlinking is safe) since the
-		 * TTL was reset to 0.
+		 * TTL will be reset to 0.
 		 */
 		ISC_LIST_UNLINK(rbtdb->rdatasets[locknum], header, link);
 		size_t header_size = rdataset_size(header);
-- 
2.44.0