From 61d3eafe98847b9a76ddc04fe7a4f63f341961a4 Mon Sep 17 00:00:00 2001
From: Bryce Kwon <bryce@brycekwon.com>
Date: Sun, 6 Sep 2026 21:40:19 -1000
Subject: Harden the lua filter failure paths

---
 source/filter.c        | 14 +++++++++-----
 tests/t0201-filters.sh | 22 ++++++++++++++++++++++
 2 files changed, 31 insertions(+), 5 deletions(-)

diff --git a/source/filter.c b/source/filter.c
index f5f971c..a7efe56 100644
--- a/source/filter.c
+++ b/source/filter.c
@@ -173,6 +173,11 @@ static inline void unhook_write(void)
 
 static NORETURN void die_lua_error(struct lua_filter *filter)
 {
+	// The error page goes out through stdout, which may still be hooked
+	// to the very filter that failed, so the hook comes off first or the
+	// page would be fed back into the broken filter.
+	if (filter_write)
+		unhook_write();
 	die("Lua error in %s: %s", filter->script_file,
 	    lua_tostring(filter->lua_state, -1));
 }
@@ -336,11 +341,10 @@ static void cleanup_lua_filter(struct cgit_filter *base)
 {
 	struct lua_filter *filter = (struct lua_filter *)base;
 
-	if (!filter->lua_state)
-		return;
-
-	lua_close(filter->lua_state);
-	filter->lua_state = NULL;
+	if (filter->lua_state) {
+		lua_close(filter->lua_state);
+		filter->lua_state = NULL;
+	}
 	free(filter->script_file);
 	filter->script_file = NULL;
 }
diff --git a/tests/t0201-filters.sh b/tests/t0201-filters.sh
index a8341aa..8d67c4f 100755
--- a/tests/t0201-filters.sh
+++ b/tests/t0201-filters.sh
@@ -65,4 +65,26 @@ do
 	"
 done
 
+test "$CGIT_HAS_LUA" -eq 1 && test_set_prereq CGIT_LUA
+test "$CGIT_HAS_LUA" -eq 1 || say 'cgit built without lua, error page check skipped'
+
+# A die inside a lua filter has to reach the visitor as an error page rather
+# than being fed back into the filter that just failed.
+test_expect_success CGIT_LUA 'a failing lua filter still renders an error page' '
+	cat >broken.lua <<-\EOF &&
+	function filter_open(...) error("boom") end
+	function filter_write(str) end
+	function filter_close() return 0 end
+	EOF
+	{
+		echo "cache-size=0" &&
+		echo "repo.url=foo" &&
+		echo "repo.path=$PWD/repos/foo/.git" &&
+		echo "auth-filter=lua:$PWD/broken.lua"
+	} >brokenrc &&
+	CGIT_CONFIG="$PWD/brokenrc" QUERY_STRING="url=foo/commit" cgit >tmp &&
+	grep "Status: 400" tmp &&
+	grep "Lua error in" tmp
+'
+
 test_done
-- 
cgit v2.8.0