From fdf465925e9b3cdd90c15a2f7fb475397f51b993 Mon Sep 17 00:00:00 2001
From: nicm <nicm>
Date: Mon, 30 Oct 2023 16:05:30 +0000
Subject: Do not allow combined UTF-8 characters that are too long, GitHub
 issue 3729.

---
 screen-write.c | 4 ++++
 1 file changed, 4 insertions(+)

(limited to 'screen-write.c')

diff --git a/screen-write.c b/screen-write.c
index 01632f61..ff758a17 100644
--- a/screen-write.c
+++ b/screen-write.c
@@ -2025,6 +2025,10 @@ screen_write_combine(struct screen_write_ctx *ctx, const struct grid_cell *gc)
 			return (0);
 	}
 
+	/* Check if this combined character would be too long. */
+	if (last.data.size + ud->size > sizeof last.data.data)
+		return (0);
+
 	/* Combining; flush any pending output. */
 	screen_write_collect_flush(ctx, 0, __func__);
 
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