From e49d3eb40324eaffaa13b93f2c4173dfa04dfa34 Mon Sep 17 00:00:00 2001
From: Alexander Motin <mav@FreeBSD.org>
Date: Tue, 13 Apr 2021 11:19:10 -0400
Subject: [PATCH] Fix race in case of device destruction.

During device destruction it is possible that open() succeed, but
fdevname() return NULL, that can't be assigned to string variable.
Fix that by adding explicit NULL check.

Also while there switch from fdevname() to fdevname_r().

Sponsored by:	iXsystems, Inc.
MFC after:	2 weeks
---
 lib/libdevdctl/event.cc | 7 ++++++-
 1 file changed, 6 insertions(+), 1 deletion(-)

diff --git a/lib/libdevdctl/event.cc b/lib/libdevdctl/event.cc
index 36c9b725fed1..76ef1896975a 100644
--- a/lib/libdevdctl/event.cc
+++ b/lib/libdevdctl/event.cc
@@ -277,6 +277,7 @@ Event::GetTimestamp() const
 bool
 Event::DevPath(std::string &path) const
 {
+	char buf[SPECNAMELEN + 1];
 	string devName;
 
 	if (!DevName(devName))
@@ -288,7 +289,11 @@ Event::DevPath(std::string &path) const
 		return (false);
 
 	/* Normalize the device name in case the DEVFS event is for a link. */
-	devName = fdevname(devFd);
+	if (fdevname_r(devFd, buf, sizeof(buf)) == NULL) {
+		close(devFd);
+		return (false);
+	}
+	devName = buf;
 	path = _PATH_DEV + devName;
 
 	close(devFd);