dhclient: support VID 0 (no vlan) decapsulation

VLAN ID 0 is supposed to be interpreted as having no VLAN with a bit of
priority on the side, but the kernel is not able to decapsulate this on
the fly so dhclient needs to take care of it.

Reviewed by:	markj

(cherry picked from commit abf5bff71d38da3c797a3b6decb426c375cc0f8f)

diff --git a/sbin/dhclient/bpf.c b/sbin/dhclient/bpf.c
index 41eb4f402e66740772f1f5fcba749bddb82d9a8b..d938b68c7c94948cec026b03de8e84de562ab802 100644 (file)
--- 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 @@ if_register_send(struct interface_info *info)
  * 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
index 21726aaaeb840611cf6147ece46cf4d6970d1712..276bb5c2457fc646aef98ee400e7818096661fa9 100644 (file)
--- a/sbin/dhclient/packet.c
+++ b/sbin/dhclient/packet.c
@@ -157,7 +157,8 @@ decode_hw_header(unsigned char *buf, int bufix, struct hardware *from)
        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