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Enable dhclient to decode 802.1q-encapsulated replies #9

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Enable dhclient to decode 802.1q-encapsulated replies #9

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33 changes: 32 additions & 1 deletion sbin/dhclient/bpf.c
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Original file line number Diff line number Diff line change
Expand Up @@ -183,6 +183,37 @@ if_register_send(struct interface_info *info)
* constant offsets used in if_register_send to patch the BPF program!
*/
struct bpf_insn dhcp_bpf_filter[] = {
/* Check for 802.1q-encapsulated packets */
BPF_STMT(BPF_LD + BPF_H + BPF_ABS, 12),
BPF_JUMP(BPF_JMP + BPF_JEQ + BPF_K, ETHERTYPE_VLAN, 0, 12),

/* We only accept packets with VID = 0 */
BPF_STMT(BPF_LD + BPF_H + BPF_ABS, 14),
BPF_STMT(BPF_ALU + BPF_AND + BPF_K, 0xfff),
BPF_JUMP(BPF_JMP + BPF_JEQ + BPF_K, 0, 0, 19),

/* Make sure this is an IP packet... */
BPF_STMT(BPF_LD + BPF_H + BPF_ABS, 16),
BPF_JUMP(BPF_JMP + BPF_JEQ + BPF_K, ETHERTYPE_IP, 0, 17),

/* Make sure it's a UDP packet... */
BPF_STMT(BPF_LD + BPF_B + BPF_ABS, 27),
BPF_JUMP(BPF_JMP + BPF_JEQ + BPF_K, IPPROTO_UDP, 0, 15),

/* Make sure this isn't a fragment... */
BPF_STMT(BPF_LD + BPF_H + BPF_ABS, 24),
BPF_JUMP(BPF_JMP + BPF_JSET + BPF_K, 0x1fff, 13, 0),

/* Get the IP header length... */
BPF_STMT(BPF_LDX + BPF_B + BPF_MSH, 18),

/* Load the target port and jump to port check below */
/* This avoids having to patch the code in two locations */
BPF_STMT(BPF_LD + BPF_H + BPF_IND, 20),
BPF_JUMP(BPF_JMP + BPF_JA, 8, 0, 0),

/* Process non-802.1q tagged packets */

/* 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),
Expand Down Expand Up @@ -259,7 +290,7 @@ if_register_receive(struct interface_info *info)
* XXX: changes to filter program may require changes to the
* insn number(s) used below!
*/
dhcp_bpf_filter[8].k = LOCAL_PORT;
dhcp_bpf_filter[22].k = LOCAL_PORT;

if (ioctl(info->rfdesc, BIOCSETF, &p) < 0)
error("Can't install packet filter program: %m");
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8 changes: 7 additions & 1 deletion sbin/dhclient/packet.c
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Original file line number Diff line number Diff line change
Expand Up @@ -155,7 +155,13 @@ decode_hw_header(unsigned char *buf, int bufix, struct hardware *from)
from->htype = ARPHRD_ETHER;
from->hlen = sizeof(eh.ether_shost);

return (sizeof(eh));
if (ntohs(eh.ether_type) == ETHERTYPE_VLAN) {
/* For 802.1q-encapsulated packets, ether_type is shifted by 4 bytes */
memcpy(&eh.ether_type, buf + bufix + 16, 2);
return (sizeof(eh)) + 4;
} else {
return (sizeof(eh));
}
}

ssize_t
Expand Down