From d2084f835172ddcdd7edc962c98f9ee6e541fd5c Mon Sep 17 00:00:00 2001
From: mvs <mvs@openbsd.org>
Date: Tue, 7 Sep 2021 16:07:46 +0000
Subject: [PATCH] Fix NULL pointer dereference introduced by previous commit.

Reported-by: syzbot+684597dbbb9b516e76ae@syzkaller.appspotmail.com

ok mpi@
---
 sys/net/rtsock.c | 18 +++++++++---------
 1 file changed, 9 insertions(+), 9 deletions(-)

diff --git a/sys/net/rtsock.c b/sys/net/rtsock.c
index 8a8a74f5a51..7cdd8fe4881 100644
--- a/sys/net/rtsock.c
+++ b/sys/net/rtsock.c
@@ -1,4 +1,4 @@
-/*	$OpenBSD: rtsock.c,v 1.320 2021/09/07 09:56:00 mvs Exp $	*/
+/*	$OpenBSD: rtsock.c,v 1.321 2021/09/07 16:07:46 mvs Exp $	*/
 /*	$NetBSD: rtsock.c,v 1.18 1996/03/29 00:32:10 cgd Exp $	*/
 
 /*
@@ -1032,14 +1032,6 @@ rtm_output(struct rt_msghdr *rtm, struct rtentry **prt,
 			rt = NULL;
 		}
 
-		ifp = if_get(rt->rt_ifidx);
-		if (ifp == NULL) {
-			rtfree(rt);
-			rt = NULL;
-			error = ESRCH;
-			break;
-		}
-
 		/*
 		 * If RTAX_GATEWAY is the argument we're trying to
 		 * change, try to find a compatible route.
@@ -1068,6 +1060,14 @@ rtm_output(struct rt_msghdr *rtm, struct rtentry **prt,
 			break;
 		}
 
+		ifp = if_get(rt->rt_ifidx);
+		if (ifp == NULL) {
+			rtfree(rt);
+			rt = NULL;
+			error = ESRCH;
+			break;
+		}
+
 		/*
 		 * RTM_CHANGE needs a perfect match.
 		 */
-- 
2.20.1