From 7bead17ddc28dbbd27424a098f3a8834500351bf Mon Sep 17 00:00:00 2001
From: Konstantin Belousov <kib@FreeBSD.org>
Date: Mon, 8 Apr 2019 18:16:49 +0000
Subject: [PATCH] Exercise some care before sending SIGHUP to mountd.

Reviewed by:	antoine, emaste, oshogbo
Sponsored by:	The FreeBSD Foundation
MFC after:	1 week
Differential revision:	https://reviews.freebsd.org/D19847
---
 sbin/mount/mount.c | 11 +++++++++++
 1 file changed, 11 insertions(+)

diff --git a/sbin/mount/mount.c b/sbin/mount/mount.c
index a44a6fe8571f..adab70d5eba5 100644
--- a/sbin/mount/mount.c
+++ b/sbin/mount/mount.c
@@ -227,6 +227,7 @@ restart_mountd(void)
 	struct pidfh *pfh;
 	pid_t mountdpid;
 
+	mountdpid = 0;
 	pfh = pidfile_open(_PATH_MOUNTDPID, 0600, &mountdpid);
 	if (pfh != NULL) {
 		/* Mountd is not running. */
@@ -237,6 +238,16 @@ restart_mountd(void)
 		/* Cannot open pidfile for some reason. */
 		return;
 	}
+
+	/*
+	 * Refuse to send broadcast or group signals, this has
+	 * happened due to the bugs in pidfile(3).
+	 */
+	if (mountdpid <= 0) {
+		warnx("mountd pid %d, refusing to send SIGHUP", mountdpid);
+		return;
+	}
+
 	/* We have mountd(8) PID in mountdpid varible, let's signal it. */
 	if (kill(mountdpid, SIGHUP) == -1)
 		err(1, "signal mountd");