From cbff793ffb280d9d11e5d7b1dc3964276491bee8 Mon Sep 17 00:00:00 2001
From: =?UTF-8?q?Zbigniew=20J=C4=99drzejewski-Szmek?= <zbyszek@in.waw.pl>
Date: Mon, 19 Dec 2022 14:36:08 +0100
Subject: [PATCH] sd-event: never pass negative errnos as signalfd to signalfd

We treat any negative value as "invalid fd", but signalfd only
accepts -1.
---
 src/libsystemd/sd-event/sd-event.c | 4 +++-
 1 file changed, 3 insertions(+), 1 deletion(-)

diff --git a/src/libsystemd/sd-event/sd-event.c b/src/libsystemd/sd-event/sd-event.c
index 299a6a2c8c..c936fcb3b6 100644
--- a/src/libsystemd/sd-event/sd-event.c
+++ b/src/libsystemd/sd-event/sd-event.c
@@ -659,7 +659,9 @@ static int event_make_signal_data(
         ss_copy = d->sigset;
         assert_se(sigaddset(&ss_copy, sig) >= 0);
 
-        r = signalfd(d->fd, &ss_copy, SFD_NONBLOCK|SFD_CLOEXEC);
+        r = signalfd(d->fd >= 0 ? d->fd : -1,   /* the first arg must be -1 or a valid signalfd */
+                     &ss_copy,
+                     SFD_NONBLOCK|SFD_CLOEXEC);
         if (r < 0) {
                 r = -errno;
                 goto fail;