From f8707400087361394703271b412477ff41583ab6 Mon Sep 17 00:00:00 2001
From: Konstantin Belousov <kib@FreeBSD.org>
Date: Wed, 27 Nov 2024 16:27:42 +0200
Subject: [PATCH] ip6_output(): if mtu is not yet computed for ipsec hook, use
 ifp mtu

Sponsored by:	NVidia networking
---
 sys/netinet6/ip6_output.c | 3 ++-
 1 file changed, 2 insertions(+), 1 deletion(-)

diff --git a/sys/netinet6/ip6_output.c b/sys/netinet6/ip6_output.c
index 7eea64bb63445e..9e4985cdc6cde3 100644
--- a/sys/netinet6/ip6_output.c
+++ b/sys/netinet6/ip6_output.c
@@ -798,7 +798,8 @@ ip6_output(struct mbuf *m0, struct ip6_pktopts *opt,
 			error = ENOBUFS;
 			goto bad;
 		}
-		if ((error = IPSEC_OUTPUT(ipv6, ifp, m, inp, mtu)) != 0) {
+		if ((error = IPSEC_OUTPUT(ipv6, ifp, m, inp, mtu == 0 ?
+		    ifp->if_mtu : mtu)) != 0) {
 			if (error == EINPROGRESS)
 				error = 0;
 			goto done;