OpenBSD-4.6/sbin/dhclient/bpf.c
/* $OpenBSD: bpf.c,v 1.20 2007/01/08 02:51:13 krw Exp $ */
/* BPF socket interface code, originally contributed by Archie Cobbs. */
/*
* Copyright (c) 1995, 1996, 1998, 1999
* The Internet Software Consortium. All rights reserved.
*
* Redistribution and use in source and binary forms, with or without
* modification, are permitted provided that the following conditions
* are met:
*
* 1. Redistributions of source code must retain the above copyright
* notice, this list of conditions and the following disclaimer.
* 2. Redistributions in binary form must reproduce the above copyright
* notice, this list of conditions and the following disclaimer in the
* documentation and/or other materials provided with the distribution.
* 3. Neither the name of The Internet Software Consortium nor the names
* of its contributors may be used to endorse or promote products derived
* from this software without specific prior written permission.
*
* THIS SOFTWARE IS PROVIDED BY THE INTERNET SOFTWARE CONSORTIUM AND
* CONTRIBUTORS ``AS IS'' AND ANY EXPRESS OR IMPLIED WARRANTIES,
* INCLUDING, BUT NOT LIMITED TO, THE IMPLIED WARRANTIES OF
* MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE ARE
* DISCLAIMED. IN NO EVENT SHALL THE INTERNET SOFTWARE CONSORTIUM OR
* CONTRIBUTORS BE LIABLE FOR ANY DIRECT, INDIRECT, INCIDENTAL,
* SPECIAL, EXEMPLARY, OR CONSEQUENTIAL DAMAGES (INCLUDING, BUT NOT
* LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS OR SERVICES; LOSS OF
* USE, DATA, OR PROFITS; OR BUSINESS INTERRUPTION) HOWEVER CAUSED AND
* ON ANY THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT LIABILITY,
* OR TORT (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY OUT
* OF THE USE OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF
* SUCH DAMAGE.
*
* This software has been written for the Internet Software Consortium
* by Ted Lemon <mellon@fugue.com> in cooperation with Vixie
* Enterprises. To learn more about the Internet Software Consortium,
* see ``http://www.vix.com/isc''. To learn more about Vixie
* Enterprises, see ``http://www.vix.com''.
*/
#include "dhcpd.h"
#include <sys/ioctl.h>
#include <sys/uio.h>
#include <net/bpf.h>
#include <netinet/in_systm.h>
#include <netinet/ip.h>
#include <netinet/udp.h>
#include <netinet/if_ether.h>
#define BPF_FORMAT "/dev/bpf%d"
/*
* Called by get_interface_list for each interface that's discovered.
* Opens a packet filter for each interface and adds it to the select
* mask.
*/
int
if_register_bpf(void)
{
char filename[50];
int sock, b;
/* Open a BPF device */
for (b = 0; 1; b++) {
snprintf(filename, sizeof(filename), BPF_FORMAT, b);
sock = open(filename, O_RDWR, 0);
if (sock < 0) {
if (errno == EBUSY)
continue;
else
error("Can't find free bpf: %m");
} else
break;
}
/* Set the BPF device to point at this interface. */
if (ioctl(sock, BIOCSETIF, ifi->ifp) < 0)
error("Can't attach interface %s to bpf device %s: %m",
ifi->name, filename);
return (sock);
}
void
if_register_send(void)
{
int sock, on = 1;
/*
* If we're using the bpf API for sending and receiving, we
* don't need to register this interface twice.
*/
ifi->wfdesc = ifi->rfdesc;
/*
* Use raw socket for unicast send.
*/
if ((sock = socket(AF_INET, SOCK_RAW, IPPROTO_UDP)) == -1)
error("socket(SOCK_RAW): %m");
if (setsockopt(sock, IPPROTO_IP, IP_HDRINCL, &on,
sizeof(on)) == -1)
error("setsockopt(IP_HDRINCL): %m");
ifi->ufdesc = sock;
}
/*
* Packet filter program...
*
* XXX: Changes to the filter program may require changes to the
* constant offsets used in if_register_send to patch the BPF program!
*/
struct bpf_insn dhcp_bpf_filter[] = {
/* 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),
/* 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),
/* Make sure this isn't a fragment... */
BPF_STMT(BPF_LD + BPF_H + BPF_ABS, 20),
BPF_JUMP(BPF_JMP + BPF_JSET + BPF_K, 0x1fff, 4, 0),
/* Get the IP header length... */
BPF_STMT(BPF_LDX + BPF_B + BPF_MSH, 14),
/* 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 */
/* If we passed all the tests, ask for the whole packet. */
BPF_STMT(BPF_RET+BPF_K, (u_int)-1),
/* Otherwise, drop it. */
BPF_STMT(BPF_RET+BPF_K, 0),
};
int dhcp_bpf_filter_len = sizeof(dhcp_bpf_filter) / sizeof(struct bpf_insn);
/*
* Packet write filter program:
* 'ip and udp and src port bootps and dst port (bootps or bootpc)'
*/
struct bpf_insn dhcp_bpf_wfilter[] = {
BPF_STMT(BPF_LD + BPF_B + BPF_IND, 14),
BPF_JUMP(BPF_JMP + BPF_JEQ + BPF_K, (IPVERSION << 4) + 5, 0, 12),
/* 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, 10),
/* 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, 8),
/* Make sure this isn't a fragment... */
BPF_STMT(BPF_LD + BPF_H + BPF_ABS, 20),
BPF_JUMP(BPF_JMP + BPF_JSET + BPF_K, 0x1fff, 6, 0), /* patched */
/* Get the IP header length... */
BPF_STMT(BPF_LDX + BPF_B + BPF_MSH, 14),
/* 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),
/* 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),
/* If we passed all the tests, ask for the whole packet. */
BPF_STMT(BPF_RET+BPF_K, (u_int)-1),
/* Otherwise, drop it. */
BPF_STMT(BPF_RET+BPF_K, 0),
};
int dhcp_bpf_wfilter_len = sizeof(dhcp_bpf_wfilter) / sizeof(struct bpf_insn);
void
if_register_receive(void)
{
struct bpf_version v;
struct bpf_program p;
int flag = 1, sz;
/* Open a BPF device and hang it on this interface... */
ifi->rfdesc = if_register_bpf();
/* Make sure the BPF version is in range... */
if (ioctl(ifi->rfdesc, BIOCVERSION, &v) < 0)
error("Can't get BPF version: %m");
if (v.bv_major != BPF_MAJOR_VERSION ||
v.bv_minor < BPF_MINOR_VERSION)
error("Kernel BPF version out of range - recompile dhcpd!");
/*
* Set immediate mode so that reads return as soon as a packet
* comes in, rather than waiting for the input buffer to fill
* with packets.
*/
if (ioctl(ifi->rfdesc, BIOCIMMEDIATE, &flag) < 0)
error("Can't set immediate mode on bpf device: %m");
if (ioctl(ifi->rfdesc, BIOCSFILDROP, &flag) < 0)
error("Can't set filter-drop mode on bpf device: %m");
/* Get the required BPF buffer length from the kernel. */
if (ioctl(ifi->rfdesc, BIOCGBLEN, &sz) < 0)
error("Can't get bpf buffer length: %m");
ifi->rbuf_max = sz;
ifi->rbuf = malloc(ifi->rbuf_max);
if (!ifi->rbuf)
error("Can't allocate %lu bytes for bpf input buffer.",
(unsigned long)ifi->rbuf_max);
ifi->rbuf_offset = 0;
ifi->rbuf_len = 0;
/* Set up the bpf filter program structure. */
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[8].k = LOCAL_PORT;
if (ioctl(ifi->rfdesc, BIOCSETF, &p) < 0)
error("Can't install packet filter program: %m");
/* Set up the bpf write filter program structure. */
p.bf_len = dhcp_bpf_wfilter_len;
p.bf_insns = dhcp_bpf_wfilter;
if (dhcp_bpf_wfilter[7].k == 0x1fff)
dhcp_bpf_wfilter[7].k = htons(IP_MF|IP_OFFMASK);
if (ioctl(ifi->rfdesc, BIOCSETWF, &p) < 0)
error("Can't install write filter program: %m");
if (ioctl(ifi->rfdesc, BIOCLOCK, NULL) < 0)
error("Cannot lock bpf");
}
ssize_t
send_packet(struct in_addr from, struct sockaddr_in *to,
struct hardware *hto)
{
#define IOVCNT 2
unsigned char buf[256];
struct iovec iov[IOVCNT];
struct msghdr msg;
int result, bufp = 0;
if (to->sin_addr.s_addr == INADDR_BROADCAST) {
assemble_hw_header(buf, &bufp, hto);
}
assemble_udp_ip_header(buf, &bufp, from.s_addr,
to->sin_addr.s_addr, to->sin_port,
(unsigned char *)&client->packet,
client->packet_length);
iov[0].iov_base = (char *)buf;
iov[0].iov_len = bufp;
iov[1].iov_base = (char *)&client->packet;
iov[1].iov_len = client->packet_length;
if (to->sin_addr.s_addr == INADDR_BROADCAST) {
result = writev(ifi->wfdesc, iov, IOVCNT);
} else {
memset(&msg, 0, sizeof(msg));
msg.msg_name = (struct sockaddr *)to;
msg.msg_namelen = sizeof(*to);
msg.msg_iov = iov;
msg.msg_iovlen = IOVCNT;
result = sendmsg(ifi->ufdesc, &msg, 0);
}
if (result == -1)
warning("send_packet: %m");
return (result);
}
ssize_t
receive_packet(struct sockaddr_in *from, struct hardware *hfrom)
{
int length = 0, offset = 0;
struct bpf_hdr hdr;
/*
* All this complexity is because BPF doesn't guarantee that
* only one packet will be returned at a time. We're getting
* what we deserve, though - this is a terrible abuse of the BPF
* interface. Sigh.
*/
/* Process packets until we get one we can return or until we've
* done a read and gotten nothing we can return...
*/
do {
/* If the buffer is empty, fill it. */
if (ifi->rbuf_offset == ifi->rbuf_len) {
length = read(ifi->rfdesc, ifi->rbuf, ifi->rbuf_max);
if (length <= 0)
return (length);
ifi->rbuf_offset = 0;
ifi->rbuf_len = BPF_WORDALIGN(length);
}
/*
* If there isn't room for a whole bpf header, something
* went wrong, but we'll ignore it and hope it goes
* away... XXX
*/
if (ifi->rbuf_len - ifi->rbuf_offset < sizeof(hdr)) {
ifi->rbuf_offset = ifi->rbuf_len;
continue;
}
/* Copy out a bpf header... */
memcpy(&hdr, &ifi->rbuf[ifi->rbuf_offset], sizeof(hdr));
/*
* If the bpf header plus data doesn't fit in what's
* left of the buffer, stick head in sand yet again...
*/
if (ifi->rbuf_offset + hdr.bh_hdrlen + hdr.bh_caplen >
ifi->rbuf_len) {
ifi->rbuf_offset = ifi->rbuf_len;
continue;
}
/*
* If the captured data wasn't the whole packet, or if
* the packet won't fit in the input buffer, all we can
* do is drop it.
*/
if (hdr.bh_caplen != hdr.bh_datalen) {
ifi->rbuf_offset = BPF_WORDALIGN(
ifi->rbuf_offset + hdr.bh_hdrlen +
hdr.bh_caplen);
continue;
}
/* Skip over the BPF header... */
ifi->rbuf_offset += hdr.bh_hdrlen;
/* Decode the physical header... */
offset = decode_hw_header(ifi->rbuf, ifi->rbuf_offset, hfrom);
/*
* If a physical layer checksum failed (dunno of any
* physical layer that supports this, but WTH), skip
* this packet.
*/
if (offset < 0) {
ifi->rbuf_offset = BPF_WORDALIGN(
ifi->rbuf_offset + hdr.bh_caplen);
continue;
}
ifi->rbuf_offset += offset;
hdr.bh_caplen -= offset;
/* Decode the IP and UDP headers... */
offset = decode_udp_ip_header(ifi->rbuf,
ifi->rbuf_offset, from, NULL, hdr.bh_caplen);
/* If the IP or UDP checksum was bad, skip the packet... */
if (offset < 0) {
ifi->rbuf_offset = BPF_WORDALIGN(
ifi->rbuf_offset + hdr.bh_caplen);
continue;
}
ifi->rbuf_offset += offset;
hdr.bh_caplen -= offset;
/*
* If there's not enough room to stash the packet data,
* we have to skip it (this shouldn't happen in real
* life, though).
*/
if (hdr.bh_caplen > sizeof(client->packet)) {
ifi->rbuf_offset = BPF_WORDALIGN(
ifi->rbuf_offset + hdr.bh_caplen);
continue;
}
/* Copy out the data in the packet... */
memset(&client->packet, DHO_END, sizeof(client->packet));
memcpy(&client->packet, ifi->rbuf + ifi->rbuf_offset,
hdr.bh_caplen);
ifi->rbuf_offset = BPF_WORDALIGN(ifi->rbuf_offset +
hdr.bh_caplen);
return (hdr.bh_caplen);
} while (!length);
return (0);
}