From e28f4e420b879d900f920a1afc7cba0bf3073618 Mon Sep 17 00:00:00 2001
From: jholdstock <jholdstock@decred.org>
Date: Wed, 11 Sep 2024 11:19:26 +0100
Subject: [PATCH] netsync: Dont let limitAdd shrink map below limit.

Without checking for pre-existing elements it was possible for limitAdd
to shrink a map below the limit.
---
 internal/netsync/manager.go | 4 ++++
 1 file changed, 4 insertions(+)

diff --git a/internal/netsync/manager.go b/internal/netsync/manager.go
index 2b3504101..f5f22b999 100644
--- a/internal/netsync/manager.go
+++ b/internal/netsync/manager.go
@@ -1690,6 +1690,10 @@ func (m *SyncManager) handleInvMsg(imsg *invMsg) {
 // evicting a random value if adding the new value would cause it to
 // overflow the maximum allowed.
 func limitAdd(m map[chainhash.Hash]struct{}, hash chainhash.Hash, limit int) {
+	// Nothing to do if entry is already in the map.
+	if _, exists := m[hash]; exists {
+		return
+	}
 	if len(m)+1 > limit {
 		// Remove a random entry from the map.  For most compilers, Go's
 		// range statement iterates starting at a random item although