Fail cleanly when a filter cannot run

A filter program that could not be run answered with two responses,
and a filter that exited without reading its input ended cgit with
the page half written.

1 file changed, 3 insertions, 0 deletions

diff --git a/source/cache.c b/source/cache.c
index 28558b1..8123e5e 100644
--- a/source/cache.c
+++ b/source/cache.c
@@ -314,6 +314,9 @@ static int fill_slot(struct cache_slot *slot)
 	slot->saved_stdout = dup(STDOUT_FILENO);
 	if (slot->saved_stdout == -1)
 		return errno;
+	// A filter program that outlives the request must not hold the client
+	// connection open.
+	fcntl(slot->saved_stdout, F_SETFD, FD_CLOEXEC);
 
 	if (dup2(slot->lock_fd, STDOUT_FILENO) == -1)
 		return errno;