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diff --git a/sbin/dhclient/bpf.c b/sbin/dhclient/bpf.c
--- a/sbin/dhclient/bpf.c
+++ b/sbin/dhclient/bpf.c
@@ -5,6 +5,7 @@
/*-
* SPDX-License-Identifier: BSD-3-Clause
*
+ * Copyright (c) 2021 Franco Fichtner <franco@opnsense.org>
* Copyright (c) 1995, 1996, 1998, 1999
* The Internet Software Consortium. All rights reserved.
*
@@ -187,20 +188,58 @@
* Packet filter program...
*/
static const struct bpf_insn dhcp_bpf_filter[] = {
+ /* Use relative index (0) for IP packet... */
+ BPF_STMT(BPF_LDX + BPF_W + BPF_IMM, 0),
+
+ /*
+ * Test whether this is a VLAN packet...
+ *
+ * In case the server packet is using a VLAN ID
+ * of 0, meaning an untagged priority was set, the
+ * response shall be read and replied to.
+ */
+ BPF_STMT(BPF_LD + BPF_H + BPF_IND, 12),
+ BPF_JUMP(BPF_JMP + BPF_JEQ + BPF_K, ETHERTYPE_VLAN, 0, 4),
+
+ /* Test whether it has a VID of 0 */
+ BPF_STMT(BPF_LD + BPF_H + BPF_IND, 14),
+ BPF_STMT(BPF_ALU + BPF_AND + BPF_K, EVL_VLID_MASK),
+ BPF_JUMP(BPF_JMP + BPF_JEQ + BPF_K, 0, 0, 17),
+
+ /* Correct the relative index for VLAN packet (4)... */
+ BPF_STMT(BPF_LDX + BPF_W + BPF_IMM, 4),
+
/* Make sure this is an IP packet... */
- BPF_STMT(BPF_LD + BPF_H + BPF_ABS, 12),
- BPF_JUMP(BPF_JMP + BPF_JEQ + BPF_K, ETHERTYPE_IP, 0, 8),
+ BPF_STMT(BPF_LD + BPF_H + BPF_IND, 12),
+ BPF_JUMP(BPF_JMP + BPF_JEQ + BPF_K, ETHERTYPE_IP, 0, 14),
/* Make sure it's a UDP packet... */
- BPF_STMT(BPF_LD + BPF_B + BPF_ABS, 23),
- BPF_JUMP(BPF_JMP + BPF_JEQ + BPF_K, IPPROTO_UDP, 0, 6),
+ BPF_STMT(BPF_LD + BPF_B + BPF_IND, 23),
+ BPF_JUMP(BPF_JMP + BPF_JEQ + BPF_K, IPPROTO_UDP, 0, 12),
/* Make sure this isn't a fragment... */
- BPF_STMT(BPF_LD + BPF_H + BPF_ABS, 20),
- BPF_JUMP(BPF_JMP + BPF_JSET + BPF_K, IP_MF|IP_OFFMASK, 4, 0),
+ BPF_STMT(BPF_LD + BPF_H + BPF_IND, 20),
+ BPF_JUMP(BPF_JMP + BPF_JSET + BPF_K, IP_MF|IP_OFFMASK, 10, 0),
- /* Get the IP header length... */
+ /*
+ * Get the IP header length...
+ *
+ * To find the correct position of the IP header
+ * length field store the index (0 or 4) in the
+ * accumulator and compare it with 0.
+ */
+ BPF_STMT(BPF_MISC + BPF_TXA, 0),
+ BPF_JUMP(BPF_JMP + BPF_JEQ + BPF_K, 0, 0, 2),
+ /* Store IP header length of IP packet in index. */
BPF_STMT(BPF_LDX + BPF_B + BPF_MSH, 14),
+ /* Skip over following VLAN handling instruction. */
+ BPF_JUMP(BPF_JMP + BPF_JA, 1, 0, 0),
+ /* Store IP header length of VLAN packet in index. */
+ BPF_STMT(BPF_LDX + BPF_B + BPF_MSH, 18),
+ /* Add IP header length to previous relative index. */
+ BPF_STMT(BPF_ALU + BPF_ADD + BPF_X, 0),
+ /* Move result back to index to reach UDP header below. */
+ BPF_STMT(BPF_MISC + BPF_TAX, 0),
/* Make sure it's to the right port... */
BPF_STMT(BPF_LD + BPF_H + BPF_IND, 16),
diff --git a/sbin/dhclient/packet.c b/sbin/dhclient/packet.c
--- a/sbin/dhclient/packet.c
+++ b/sbin/dhclient/packet.c
@@ -157,7 +157,8 @@
from->htype = ARPHRD_ETHER;
from->hlen = sizeof(eh.ether_shost);
- return (sizeof(eh));
+ return (sizeof(eh) + (ntohs(eh.ether_type) == ETHERTYPE_VLAN ?
+ ETHER_VLAN_ENCAP_LEN : 0));
}
ssize_t

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