From 2e9c6c25869f0156aac20771f4a5f94a0496d642 Mon Sep 17 00:00:00 2001
From: nicm <nicm>
Date: Fri, 1 May 2026 11:56:41 +0000
Subject: [PATCH] Add some checks on line size to avoid underflow, from
 san65384 at gmail dot com in GitHub issue 4955.

---
 mode-tree.c | 8 ++++++++
 1 file changed, 8 insertions(+)

diff --git a/mode-tree.c b/mode-tree.c
index bf0b163c..6479d78d 100644
--- a/mode-tree.c
+++ b/mode-tree.c
@@ -301,6 +301,8 @@ mode_tree_clear_tagged(struct mode_tree_list *mtl)
 void
 mode_tree_up(struct mode_tree_data *mtd, int wrap)
 {
+	if (mtd->line_size == 0)
+		return;
 	if (mtd->current == 0) {
 		if (wrap) {
 			mtd->current = mtd->line_size - 1;
@@ -317,6 +319,8 @@ mode_tree_up(struct mode_tree_data *mtd, int wrap)
 int
 mode_tree_down(struct mode_tree_data *mtd, int wrap)
 {
+	if (mtd->line_size == 0)
+		return (0);
 	if (mtd->current == mtd->line_size - 1) {
 		if (wrap) {
 			mtd->current = 0;
@@ -363,6 +367,8 @@ mode_tree_swap(struct mode_tree_data *mtd, int direction)
 void *
 mode_tree_get_current(struct mode_tree_data *mtd)
 {
+	if (mtd->line_size == 0)
+		return (NULL);
 	return (mtd->line_list[mtd->current].item->itemdata);
 }
 
@@ -433,6 +439,8 @@ mode_tree_set_current(struct mode_tree_data *mtd, uint64_t tag)
 		return (1);
 	}
 	if (mtd->current >= mtd->line_size) {
+		if (mtd->line_size == 0)
+			return (0);
 		mtd->current = mtd->line_size - 1;
 		if (mtd->current > mtd->height - 1)
 			mtd->offset = mtd->current - mtd->height + 1;