From 499bfea65d00a4bd113fed3051ff6db5ed8e4fb5 Mon Sep 17 00:00:00 2001
From: Michael Tuexen <tuexen@FreeBSD.org>
Date: Mon, 18 Aug 2025 19:15:39 +0200
Subject: [PATCH] icmp: clear offset and flags when reflecting a packet

When reflecting a packet, use an offset of 0 and clear all three bits,
in particular the DF bit.

PR:			288558
Reviewed by:		markj, zlei
Sponsored by:		Netflix, Inc.
Differential Revision:	https://reviews.freebsd.org/D51991

(cherry picked from commit b9a2d84b1bf7f9cf556e2f0b68023d5af8362797)
---
 sys/netinet/ip_icmp.c | 3 ++-
 1 file changed, 2 insertions(+), 1 deletion(-)

diff --git a/sys/netinet/ip_icmp.c b/sys/netinet/ip_icmp.c
index 122293a36a1..84780b7859a 100644
--- a/sys/netinet/ip_icmp.c
+++ b/sys/netinet/ip_icmp.c
@@ -393,7 +393,6 @@ stdreply:	icmpelen = max(8, min(V_icmp_quotelen, ntohs(oip->ip_len) -
 	nip->ip_hl = 5;
 	nip->ip_p = IPPROTO_ICMP;
 	nip->ip_tos = 0;
-	nip->ip_off = 0;
 
 	if (V_error_keeptags)
 		m_tag_copy_chain(m, n, M_NOWAIT);
@@ -879,6 +878,8 @@ match:
 	mac_netinet_icmp_replyinplace(m);
 #endif
 	ip->ip_src = t;
+	/* ip->ip_tos will be reflected. */
+	ip->ip_off = htons(0);
 	ip->ip_ttl = V_ip_defttl;
 
 	if (optlen > 0) {