From bb99396c1fa0f6dced83f6d6ac91fc638b00e5a1 Mon Sep 17 00:00:00 2001
From: Franco Fichtner <franco@opnsense.org>
Date: Thu, 10 Jun 2021 15:11:50 +0200
Subject: [PATCH] dhclient: these ancient patches make no sense to me

Imported into FreeBSD from OpenBSD 3.7.  Imported in 2004 from
ISC DHCP...  Looks like the patching was part of templating for
different things, sort of see:

https://gitlab.isc.org/isc-projects/dhcp/-/blob/master/common/bpf.c

At least we know the BPF filter values should be given in host
order and apparently the whole thing keeps working.

While here enable the IP_MF bit reading which seems to be cool.
---
 sbin/dhclient/bpf.c | 20 +++++---------------
 1 file changed, 5 insertions(+), 15 deletions(-)

diff --git a/sbin/dhclient/bpf.c b/sbin/dhclient/bpf.c
index 23561104ced..6f97a9c7bba 100644
--- a/sbin/dhclient/bpf.c
+++ b/sbin/dhclient/bpf.c
@@ -121,7 +121,7 @@ static struct bpf_insn dhcp_bpf_wfilter[] = {
 
 	/* Make sure this isn't a fragment... */
 	BPF_STMT(BPF_LD + BPF_H + BPF_IND, 20),
-	BPF_JUMP(BPF_JMP + BPF_JSET + BPF_K, 0x1fff, 12, 0),	/* patched */
+	BPF_JUMP(BPF_JMP + BPF_JSET + BPF_K, IP_MF|IP_OFFMASK, 12, 0),
 
 	/* Get the IP header length... */
 	BPF_STMT(BPF_MISC + BPF_TXA, 0),
@@ -134,11 +134,11 @@ static struct bpf_insn dhcp_bpf_wfilter[] = {
 
 	/* Make sure it's from the right port... */
 	BPF_STMT(BPF_LD + BPF_H + BPF_IND, 14),
-	BPF_JUMP(BPF_JMP + BPF_JEQ + BPF_K, 68, 0, 3),
+	BPF_JUMP(BPF_JMP + BPF_JEQ + BPF_K, LOCAL_PORT, 0, 3),
 
 	/* Make sure it is to the right ports ... */
 	BPF_STMT(BPF_LD + BPF_H + BPF_IND, 16),
-	BPF_JUMP(BPF_JMP + BPF_JEQ + BPF_K, 67, 0, 1),
+	BPF_JUMP(BPF_JMP + BPF_JEQ + BPF_K, REMOTE_PORT, 0, 1),
 
 	/* If we passed all the tests, ask for the whole packet. */
 	BPF_STMT(BPF_RET+BPF_K, (u_int)-1),
@@ -172,9 +172,6 @@ if_register_send(struct interface_info *info)
 	p.bf_len = dhcp_bpf_wfilter_len;
 	p.bf_insns = dhcp_bpf_wfilter;
 
-	if (dhcp_bpf_wfilter[11].k == 0x1fff)
-		dhcp_bpf_wfilter[11].k = htons(IP_MF|IP_OFFMASK);
-
 	if (ioctl(info->wfdesc, BIOCSETWF, &p) < 0)
 		error("Can't install write filter program: %m");
 
@@ -228,7 +225,7 @@ static struct bpf_insn dhcp_bpf_filter[] = {
 
 	/* Make sure this isn't a fragment... */
 	BPF_STMT(BPF_LD + BPF_H + BPF_IND, 20),
-	BPF_JUMP(BPF_JMP + BPF_JSET + BPF_K, 0x1fff, 10, 0),
+	BPF_JUMP(BPF_JMP + BPF_JSET + BPF_K, IP_MF|IP_OFFMASK, 10, 0),
 
 	/* Get the IP header length... */
 	BPF_STMT(BPF_MISC + BPF_TXA, 0),
@@ -241,7 +238,7 @@ static struct bpf_insn dhcp_bpf_filter[] = {
 
 	/* Make sure it's to the right port... */
 	BPF_STMT(BPF_LD + BPF_H + BPF_IND, 16),
-	BPF_JUMP(BPF_JMP + BPF_JEQ + BPF_K, 67, 0, 1),		/* patch */
+	BPF_JUMP(BPF_JMP + BPF_JEQ + BPF_K, LOCAL_PORT, 0, 1),
 
 	/* If we passed all the tests, ask for the whole packet. */
 	BPF_STMT(BPF_RET+BPF_K, (u_int)-1),
@@ -295,13 +292,6 @@ if_register_receive(struct interface_info *info)
 	p.bf_len = dhcp_bpf_filter_len;
 	p.bf_insns = dhcp_bpf_filter;
 
-	/* Patch the server port into the BPF program...
-	 *
-	 * XXX: changes to filter program may require changes to the
-	 * insn number(s) used below!
-	 */
-	dhcp_bpf_filter[21].k = LOCAL_PORT;
-
 	if (ioctl(info->rfdesc, BIOCSETF, &p) < 0)
 		error("Can't install packet filter program: %m");