OpenBSD-4.6/usr.sbin/dhcpd/bpf.c
/* $OpenBSD: bpf.c,v 1.7 2008/09/15 20:38:17 claudio 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(struct interface_info *info)
{
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 == -1) {
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, info->ifp) == -1)
error("Can't attach interface %s to bpf device %s: %m",
info->name, filename);
return (sock);
}
void
if_register_send(struct interface_info *info)
{
/*
* If we're using the bpf API for sending and receiving, we
* don't need to register this interface twice.
*/
info->wfdesc = info->rfdesc;
}
/*
* Packet read filter program: 'ip and udp and dst port bootps'
*/
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, SERVER_PORT, 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_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[] = {
/* 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, 11),
/* 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, 9),
/* 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, 7, 0),
/* 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, SERVER_PORT, 0, 4),
/* 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, CLIENT_PORT, 1, 0),
BPF_JUMP(BPF_JMP + BPF_JEQ + BPF_K, SERVER_PORT, 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(struct interface_info *info)
{
struct bpf_version v;
struct bpf_program p;
int flag = 1, sz, cmplt = 0;
/* Open a BPF device and hang it on this interface... */
info->rfdesc = if_register_bpf(info);
/* Make sure the BPF version is in range... */
if (ioctl(info->rfdesc, BIOCVERSION, &v) == -1)
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(info->rfdesc, BIOCIMMEDIATE, &flag) == -1)
error("Can't set immediate mode on bpf device: %m");
/* make sure kernel fills in the source ethernet address */
if (ioctl(info->rfdesc, BIOCSHDRCMPLT, &cmplt) == -1)
error("Can't set header complete flag on bpf device: %m");
/* Get the required BPF buffer length from the kernel. */
if (ioctl(info->rfdesc, BIOCGBLEN, &sz) == -1)
error("Can't get bpf buffer length: %m");
info->rbuf_max = sz;
info->rbuf = malloc(info->rbuf_max);
if (!info->rbuf)
error("Can't allocate %lu bytes for bpf input buffer.",
(unsigned long)info->rbuf_max);
info->rbuf_offset = 0;
info->rbuf_len = 0;
/* Set up the bpf filter program structure. */
p.bf_len = dhcp_bpf_filter_len;
p.bf_insns = dhcp_bpf_filter;
if (ioctl(info->rfdesc, BIOCSETF, &p) == -1)
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 (ioctl(info->rfdesc, BIOCSETWF, &p) == -1)
error("Can't install write filter program: %m");
/* make sure these settings cannot be changed after dropping privs */
if (ioctl(info->rfdesc, BIOCLOCK) == -1)
error("Failed to lock bpf descriptor: %m");
}
ssize_t
send_packet(struct interface_info *interface, struct dhcp_packet *raw,
size_t len, struct in_addr from, struct sockaddr_in *to,
struct hardware *hto)
{
unsigned char buf[256];
struct iovec iov[2];
int result, bufp = 0;
/* Assemble the headers... */
assemble_hw_header(interface, buf, &bufp, hto);
assemble_udp_ip_header(interface, buf, &bufp, from.s_addr,
to->sin_addr.s_addr, to->sin_port, (unsigned char *)raw, len);
/* Fire it off */
iov[0].iov_base = (char *)buf;
iov[0].iov_len = bufp;
iov[1].iov_base = (char *)raw;
iov[1].iov_len = len;
result = writev(interface->wfdesc, iov, 2);
if (result == -1)
warning("send_packet: %m");
return (result);
}
ssize_t
receive_packet(struct interface_info *interface, unsigned char *buf,
size_t len, 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 (interface->rbuf_offset == interface->rbuf_len) {
length = read(interface->rfdesc, interface->rbuf,
interface->rbuf_max);
if (length <= 0)
return (length);
interface->rbuf_offset = 0;
interface->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 (interface->rbuf_len - interface->rbuf_offset <
sizeof(hdr)) {
interface->rbuf_offset = interface->rbuf_len;
continue;
}
/* Copy out a bpf header... */
memcpy(&hdr, &interface->rbuf[interface->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 (interface->rbuf_offset + hdr.bh_hdrlen + hdr.bh_caplen >
interface->rbuf_len) {
interface->rbuf_offset = interface->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) {
interface->rbuf_offset = BPF_WORDALIGN(
interface->rbuf_offset + hdr.bh_hdrlen +
hdr.bh_caplen);
continue;
}
/* Skip over the BPF header... */
interface->rbuf_offset += hdr.bh_hdrlen;
/* Decode the physical header... */
offset = decode_hw_header(interface,
interface->rbuf, interface->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) {
interface->rbuf_offset = BPF_WORDALIGN(
interface->rbuf_offset + hdr.bh_caplen);
continue;
}
interface->rbuf_offset += offset;
hdr.bh_caplen -= offset;
/* Decode the IP and UDP headers... */
offset = decode_udp_ip_header(interface, interface->rbuf,
interface->rbuf_offset, from, NULL, hdr.bh_caplen);
/* If the IP or UDP checksum was bad, skip the packet... */
if (offset < 0) {
interface->rbuf_offset = BPF_WORDALIGN(
interface->rbuf_offset + hdr.bh_caplen);
continue;
}
interface->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 > len) {
interface->rbuf_offset = BPF_WORDALIGN(
interface->rbuf_offset + hdr.bh_caplen);
continue;
}
/* Copy out the data in the packet... */
memcpy(buf, interface->rbuf + interface->rbuf_offset,
hdr.bh_caplen);
interface->rbuf_offset = BPF_WORDALIGN(interface->rbuf_offset +
hdr.bh_caplen);
return (hdr.bh_caplen);
} while (!length);
return (0);
}