From 303edb71bda9515605e41bdb323203bc24d15c90 Mon Sep 17 00:00:00 2001
From: nicm <nicm>
Date: Wed, 22 Apr 2026 07:05:03 +0000
Subject: [PATCH] Add a fairly low time limit to format evaluation to stop
 absurdly nested formats from making tmux appear to hang.

---
 format.c | 16 +++++++++++++++-
 1 file changed, 15 insertions(+), 1 deletion(-)

diff --git a/format.c b/format.c
index 88fb227a..90537879 100644
--- a/format.c
+++ b/format.c
@@ -120,6 +120,9 @@ format_job_cmp(struct format_job *fj1, struct format_job *fj2)
 /* Limit on recursion. */
 #define FORMAT_LOOP_LIMIT 100
 
+/* Limit on time taken (milliseconds). */
+#define FORMAT_TIME_LIMIT 100
+
 /* Format expand flags. */
 #define FORMAT_EXPAND_TIME 0x1
 #define FORMAT_EXPAND_NOJOBS 0x2
@@ -169,9 +172,11 @@ RB_GENERATE_STATIC(format_entry_tree, format_entry, entry, format_entry_cmp);
 struct format_expand_state {
 	struct format_tree	*ft;
 	u_int			 loop;
+	uint64_t		 start_time;
+	int			 flags;
+
 	time_t			 time;
 	struct tm		 tm;
-	int			 flags;
 };
 
 /* Format modifier. */
@@ -292,6 +297,7 @@ format_copy_state(struct format_expand_state *to,
 	to->time = from->time;
 	memcpy(&to->tm, &from->tm, sizeof to->tm);
 	to->flags = from->flags|flags;
+	to->start_time = from->start_time;
 }
 
 /* Format job update callback. */
@@ -5514,10 +5520,16 @@ format_expand1(struct format_expand_state *es, const char *fmt)
 	size_t			 off, len, n, outlen;
 	int			 ch, brackets;
 	char			 expanded[8192];
+	uint64_t		 t = get_timer();
 
 	if (fmt == NULL || *fmt == '\0')
 		return (xstrdup(""));
 
+	if (t - es->start_time >= FORMAT_TIME_LIMIT) {
+		format_log(es, "reached time limit (%llu)",
+		    (unsigned long long)(t - es->start_time));
+		return (xstrdup(""));
+	}
 	if (es->loop == FORMAT_LOOP_LIMIT) {
 		format_log(es, "reached loop limit (%u)", FORMAT_LOOP_LIMIT);
 		return (xstrdup(""));
@@ -5683,6 +5695,7 @@ format_expand_time(struct format_tree *ft, const char *fmt)
 	memset(&es, 0, sizeof es);
 	es.ft = ft;
 	es.flags = FORMAT_EXPAND_TIME;
+	es.start_time = get_timer();
 	return (format_expand1(&es, fmt));
 }
 
@@ -5695,6 +5708,7 @@ format_expand(struct format_tree *ft, const char *fmt)
 	memset(&es, 0, sizeof es);
 	es.ft = ft;
 	es.flags = 0;
+	es.start_time = get_timer();
 	return (format_expand1(&es, fmt));
 }