xref: /dflybsd-src/contrib/dhcpcd/src/bpf.c (revision 5422d4140b73a6e65966a6f40831066aa79c4714)

/* SPDX-License-Identifier: BSD-2-Clause */
/*
 * dhcpcd: BPF arp and bootp filtering
 * Copyright (c) 2006-2023 Roy Marples <roy@marples.name>
 * 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.
 *
 * THIS SOFTWARE IS PROVIDED BY THE AUTHOR 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 AUTHOR 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.
 */

#include <sys/ioctl.h>
#include <sys/socket.h>

#include <arpa/inet.h>

#include <net/if.h>
#include <netinet/in.h>
#include <netinet/if_ether.h>

#ifdef __linux__
/* Special BPF snowflake. */
#include <linux/filter.h>
#define	bpf_insn		sock_filter
#else
#include <net/bpf.h>
#endif

#include <errno.h>
#include <fcntl.h>
#include <stddef.h>
#include <stdlib.h>
#include <string.h>

#include "common.h"
#include "arp.h"
#include "bpf.h"
#include "dhcp.h"
#include "if.h"
#include "logerr.h"

/* BPF helper macros */
#ifdef __linux__
#define	BPF_WHOLEPACKET		0x7fffffff /* work around buggy LPF filters */
#else
#define	BPF_WHOLEPACKET		~0U
#endif

/* Macros to update the BPF structure */
#define	BPF_SET_STMT(insn, c, v) {				\
	(insn)->code = (c);					\
	(insn)->jt = 0;						\
	(insn)->jf = 0;						\
	(insn)->k = (uint32_t)(v);				\
}

#define	BPF_SET_JUMP(insn, c, v, t, f) {			\
	(insn)->code = (c);					\
	(insn)->jt = (t);					\
	(insn)->jf = (f);					\
	(insn)->k = (uint32_t)(v);				\
}

size_t
bpf_frame_header_len(const struct interface *ifp)
{

	switch (ifp->hwtype) {
	case ARPHRD_ETHER:
		return sizeof(struct ether_header);
	default:
		return 0;
	}
}

void *
bpf_frame_header_src(const struct interface *ifp, void *fh, size_t *len)
{
	uint8_t *f = fh;

	switch (ifp->hwtype) {
	case ARPHRD_ETHER:
		*len = sizeof(((struct ether_header *)0)->ether_shost);
		return f + offsetof(struct ether_header, ether_shost);
	default:
		*len = 0;
		errno =	ENOTSUP;
		return NULL;
	}
}

void *
bpf_frame_header_dst(const struct interface *ifp, void *fh, size_t *len)
{
	uint8_t *f = fh;

	switch (ifp->hwtype) {
	case ARPHRD_ETHER:
		*len = sizeof(((struct ether_header *)0)->ether_dhost);
		return f + offsetof(struct ether_header, ether_dhost);
	default:
		*len = 0;
		errno =	ENOTSUP;
		return NULL;
	}
}

static const uint8_t etherbcastaddr[] =
    { 0xff, 0xff, 0xff, 0xff, 0xff, 0xff };

int
bpf_frame_bcast(const struct interface *ifp, const void *frame)
{

	switch (ifp->hwtype) {
	case ARPHRD_ETHER:
		return memcmp((const char *)frame +
		    offsetof(struct ether_header, ether_dhost),
		    etherbcastaddr, sizeof(etherbcastaddr));
	default:
		return -1;
	}
}

#ifndef __linux__
/* Linux is a special snowflake for opening, attaching and reading BPF.
 * See if-linux.c for the Linux specific BPF functions. */

const char *bpf_name = "Berkley Packet Filter";

struct bpf *
bpf_open(const struct interface *ifp,
    int (*filter)(const struct bpf *, const struct in_addr *),
    const struct in_addr *ia)
{
	struct bpf *bpf;
	struct bpf_version pv = { .bv_major = 0, .bv_minor = 0 };
	struct ifreq ifr = { .ifr_flags = 0 };
	int ibuf_len = 0;
#ifdef O_CLOEXEC
#define BPF_OPEN_FLAGS O_RDWR | O_NONBLOCK | O_CLOEXEC
#else
#define BPF_OPEN_FLAGS O_RDWR | O_NONBLOCK
#endif
#ifdef BIOCIMMEDIATE
	unsigned int flags;
#endif
#ifndef O_CLOEXEC
	int fd_opts;
#endif

	bpf = calloc(1, sizeof(*bpf));
	if (bpf == NULL)
		return NULL;
	bpf->bpf_ifp = ifp;

	/* /dev/bpf is a cloner on modern kernels */
	bpf->bpf_fd = open("/dev/bpf", BPF_OPEN_FLAGS);

	/* Support older kernels where /dev/bpf is not a cloner */
	if (bpf->bpf_fd == -1) {
		char device[32];
		int n = 0;

		do {
			snprintf(device, sizeof(device), "/dev/bpf%d", n++);
			bpf->bpf_fd = open(device, BPF_OPEN_FLAGS);
		} while (bpf->bpf_fd == -1 && errno == EBUSY);
	}

	if (bpf->bpf_fd == -1)
		goto eexit;

#ifndef O_CLOEXEC
	if ((fd_opts = fcntl(bpf->bpf_fd, F_GETFD)) == -1 ||
	    fcntl(bpf->bpf_fd, F_SETFD, fd_opts | FD_CLOEXEC) == -1)
		goto eexit;
#endif

	if (ioctl(bpf->bpf_fd, BIOCVERSION, &pv) == -1)
		goto eexit;
	if (pv.bv_major != BPF_MAJOR_VERSION ||
	    pv.bv_minor < BPF_MINOR_VERSION) {
		logerrx("BPF version mismatch - recompile");
		goto eexit;
	}

	strlcpy(ifr.ifr_name, ifp->name, sizeof(ifr.ifr_name));
	if (ioctl(bpf->bpf_fd, BIOCSETIF, &ifr) == -1)
		goto eexit;

#ifdef BIOCIMMEDIATE
	flags = 1;
	if (ioctl(bpf->bpf_fd, BIOCIMMEDIATE, &flags) == -1)
		goto eexit;
#endif

	if (filter(bpf, ia) != 0)
		goto eexit;

	/* Get the required BPF buffer length from the kernel. */
	if (ioctl(bpf->bpf_fd, BIOCGBLEN, &ibuf_len) == -1)
		goto eexit;
	bpf->bpf_size = (size_t)ibuf_len;
	bpf->bpf_buffer = malloc(bpf->bpf_size);
	if (bpf->bpf_buffer == NULL)
		goto eexit;
	return bpf;

eexit:
	if (bpf->bpf_fd != -1)
		close(bpf->bpf_fd);
	free(bpf);
	return NULL;
}

/* BPF requires that we read the entire buffer.
 * So we pass the buffer in the API so we can loop on >1 packet. */
ssize_t
bpf_read(struct bpf *bpf, void *data, size_t len)
{
	ssize_t bytes;
	struct bpf_hdr packet;
	const char *payload;

	bpf->bpf_flags &= ~BPF_EOF;
	for (;;) {
		if (bpf->bpf_len == 0) {
			bytes = read(bpf->bpf_fd, bpf->bpf_buffer,
			    bpf->bpf_size);
#if defined(__sun)
			/* After 2^31 bytes, the kernel offset overflows.
			 * To work around this bug, lseek 0. */
			if (bytes == -1 && errno == EINVAL) {
				lseek(bpf->bpf_fd, 0, SEEK_SET);
				continue;
			}
#endif
			if (bytes == -1 || bytes == 0)
				return bytes;
			bpf->bpf_len = (size_t)bytes;
			bpf->bpf_pos = 0;
		}
		bytes = -1;
		payload = (const char *)bpf->bpf_buffer + bpf->bpf_pos;
		memcpy(&packet, payload, sizeof(packet));
		if (bpf->bpf_pos + packet.bh_caplen + packet.bh_hdrlen >
		    bpf->bpf_len)
			goto next; /* Packet beyond buffer, drop. */
		payload += packet.bh_hdrlen;
		if (packet.bh_caplen > len)
			bytes = (ssize_t)len;
		else
			bytes = (ssize_t)packet.bh_caplen;
		if (bpf_frame_bcast(bpf->bpf_ifp, payload) == 0)
			bpf->bpf_flags |= BPF_BCAST;
		else
			bpf->bpf_flags &= ~BPF_BCAST;
		memcpy(data, payload, (size_t)bytes);
next:
		bpf->bpf_pos += BPF_WORDALIGN(packet.bh_hdrlen +
		    packet.bh_caplen);
		if (bpf->bpf_pos >= bpf->bpf_len) {
			bpf->bpf_len = bpf->bpf_pos = 0;
			bpf->bpf_flags |= BPF_EOF;
		}
		if (bytes != -1)
			return bytes;
	}

	/* NOTREACHED */
}

int
bpf_attach(int fd, void *filter, unsigned int filter_len)
{
	struct bpf_program pf = { .bf_insns = filter, .bf_len = filter_len };

	/* Install the filter. */
	return ioctl(fd, BIOCSETF, &pf);
}

#ifdef BIOCSETWF
static int
bpf_wattach(int fd, void *filter, unsigned int filter_len)
{
	struct bpf_program pf = { .bf_insns = filter, .bf_len = filter_len };

	/* Install the filter. */
	return ioctl(fd, BIOCSETWF, &pf);
}
#endif
#endif

#ifndef __sun
/* SunOS is special too - sending via BPF goes nowhere. */
ssize_t
bpf_send(const struct bpf *bpf, uint16_t protocol,
    const void *data, size_t len)
{
	struct iovec iov[2];
	struct ether_header eh;

	switch(bpf->bpf_ifp->hwtype) {
	case ARPHRD_ETHER:
		memset(&eh.ether_dhost, 0xff, sizeof(eh.ether_dhost));
		memcpy(&eh.ether_shost, bpf->bpf_ifp->hwaddr,
		    sizeof(eh.ether_shost));
		eh.ether_type = htons(protocol);
		iov[0].iov_base = &eh;
		iov[0].iov_len = sizeof(eh);
		break;
	default:
		iov[0].iov_base = NULL;
		iov[0].iov_len = 0;
		break;
	}
	iov[1].iov_base = UNCONST(data);
	iov[1].iov_len = len;
	return writev(bpf->bpf_fd, iov, 2);
}
#endif

void
bpf_close(struct bpf *bpf)
{

	close(bpf->bpf_fd);
	free(bpf->bpf_buffer);
	free(bpf);
}

#ifdef ARP
#define BPF_CMP_HWADDR_LEN	((((HWADDR_LEN / 4) + 2) * 2) + 1)
static unsigned int
bpf_cmp_hwaddr(struct bpf_insn *bpf, size_t bpf_len, size_t off,
    bool equal, const uint8_t *hwaddr, size_t hwaddr_len)
{
	struct bpf_insn *bp;
	size_t maclen, nlft, njmps;
	uint32_t mac32;
	uint16_t mac16;
	uint8_t jt, jf;

	/* Calc the number of jumps */
	if ((hwaddr_len / 4) >= 128) {
		errno = EINVAL;
		return 0;
	}
	njmps = (hwaddr_len / 4) * 2; /* 2 instructions per check */
	/* We jump after the 1st check. */
	if (njmps)
		njmps -= 2;
	nlft = hwaddr_len % 4;
	if (nlft) {
		njmps += (nlft / 2) * 2;
		nlft = nlft % 2;
		if (nlft)
			njmps += 2;

	}

	/* Skip to positive finish. */
	njmps++;
	if (equal) {
		jt = (uint8_t)njmps;
		jf = 0;
	} else {
		jt = 0;
		jf = (uint8_t)njmps;
	}

	bp = bpf;
	for (; hwaddr_len > 0;
	     hwaddr += maclen, hwaddr_len -= maclen, off += maclen)
	{
		if (bpf_len < 3) {
			errno = ENOBUFS;
			return 0;
		}
		bpf_len -= 3;

		if (hwaddr_len >= 4) {
			maclen = sizeof(mac32);
			memcpy(&mac32, hwaddr, maclen);
			BPF_SET_STMT(bp, BPF_LD + BPF_W + BPF_IND, off);
			bp++;
			BPF_SET_JUMP(bp, BPF_JMP + BPF_JEQ + BPF_K,
			             htonl(mac32), jt, jf);
		} else if (hwaddr_len >= 2) {
			maclen = sizeof(mac16);
			memcpy(&mac16, hwaddr, maclen);
			BPF_SET_STMT(bp, BPF_LD + BPF_H + BPF_IND, off);
			bp++;
			BPF_SET_JUMP(bp, BPF_JMP + BPF_JEQ + BPF_K,
			             htons(mac16), jt, jf);
		} else {
			maclen = sizeof(*hwaddr);
			BPF_SET_STMT(bp, BPF_LD + BPF_B + BPF_IND, off);
			bp++;
			BPF_SET_JUMP(bp, BPF_JMP + BPF_JEQ + BPF_K,
			             *hwaddr, jt, jf);
		}
		if (jt)
			jt = (uint8_t)(jt - 2);
		if (jf)
			jf = (uint8_t)(jf - 2);
		bp++;
	}

	/* Last step is always return failure.
	 * Next step is a positive finish. */
	BPF_SET_STMT(bp, BPF_RET + BPF_K, 0);
	bp++;

	return (unsigned int)(bp - bpf);
}
#endif

#ifdef ARP
static const struct bpf_insn bpf_arp_ether [] = {
	/* Check this is an ARP packet. */
	BPF_STMT(BPF_LD + BPF_H + BPF_ABS,
	         offsetof(struct ether_header, ether_type)),
	BPF_JUMP(BPF_JMP + BPF_JEQ + BPF_K, ETHERTYPE_ARP, 1, 0),
	BPF_STMT(BPF_RET + BPF_K, 0),

	/* Load frame header length into X */
	BPF_STMT(BPF_LDX + BPF_W + BPF_IMM, sizeof(struct ether_header)),

	/* Make sure the hardware type matches. */
	BPF_STMT(BPF_LD + BPF_H + BPF_IND, offsetof(struct arphdr, ar_hrd)),
	BPF_JUMP(BPF_JMP + BPF_JEQ + BPF_K, ARPHRD_ETHER, 1, 0),
	BPF_STMT(BPF_RET + BPF_K, 0),

	/* Make sure the hardware length matches. */
	BPF_STMT(BPF_LD + BPF_B + BPF_IND, offsetof(struct arphdr, ar_hln)),
	BPF_JUMP(BPF_JMP + BPF_JEQ + BPF_K,
	         sizeof(((struct ether_arp *)0)->arp_sha), 1, 0),
	BPF_STMT(BPF_RET + BPF_K, 0),
};
#define BPF_ARP_ETHER_LEN	__arraycount(bpf_arp_ether)

static const struct bpf_insn bpf_arp_filter [] = {
	/* Make sure this is for IP. */
	BPF_STMT(BPF_LD + BPF_H + BPF_IND, offsetof(struct arphdr, ar_pro)),
	BPF_JUMP(BPF_JMP + BPF_JEQ + BPF_K, ETHERTYPE_IP, 1, 0),
	BPF_STMT(BPF_RET + BPF_K, 0),
	/* Make sure this is an ARP REQUEST. */
	BPF_STMT(BPF_LD + BPF_H + BPF_IND, offsetof(struct arphdr, ar_op)),
	BPF_JUMP(BPF_JMP + BPF_JEQ + BPF_K, ARPOP_REQUEST, 2, 0),
	/* or ARP REPLY. */
	BPF_JUMP(BPF_JMP + BPF_JEQ + BPF_K, ARPOP_REPLY, 1, 0),
	BPF_STMT(BPF_RET + BPF_K, 0),
	/* Make sure the protocol length matches. */
	BPF_STMT(BPF_LD + BPF_B + BPF_IND, offsetof(struct arphdr, ar_pln)),
	BPF_JUMP(BPF_JMP + BPF_JEQ + BPF_K, sizeof(in_addr_t), 1, 0),
	BPF_STMT(BPF_RET + BPF_K, 0),
};
#define BPF_ARP_FILTER_LEN	__arraycount(bpf_arp_filter)

/* One address is two checks of two statements. */
#define BPF_NADDRS		1
#define BPF_ARP_ADDRS_LEN	5 + ((BPF_NADDRS * 2) * 2)

#define BPF_ARP_LEN		BPF_ARP_ETHER_LEN + BPF_ARP_FILTER_LEN + \
				BPF_CMP_HWADDR_LEN + BPF_ARP_ADDRS_LEN

static int
bpf_arp_rw(const struct bpf *bpf, const struct in_addr *ia, bool recv)
{
	const struct interface *ifp = bpf->bpf_ifp;
	struct bpf_insn buf[BPF_ARP_LEN + 1];
	struct bpf_insn *bp;
	uint16_t arp_len;

	bp = buf;
	/* Check frame header. */
	switch(ifp->hwtype) {
	case ARPHRD_ETHER:
		memcpy(bp, bpf_arp_ether, sizeof(bpf_arp_ether));
		bp += BPF_ARP_ETHER_LEN;
		arp_len = sizeof(struct ether_header)+sizeof(struct ether_arp);
		break;
	default:
		errno = EINVAL;
		return -1;
	}

	/* Copy in the main filter. */
	memcpy(bp, bpf_arp_filter, sizeof(bpf_arp_filter));
	bp += BPF_ARP_FILTER_LEN;

	/* Ensure it's not from us. */
	bp += bpf_cmp_hwaddr(bp, BPF_CMP_HWADDR_LEN, sizeof(struct arphdr),
	                     !recv, ifp->hwaddr, ifp->hwlen);

	/* Match sender protocol address */
	BPF_SET_STMT(bp, BPF_LD + BPF_W + BPF_IND,
	    sizeof(struct arphdr) + ifp->hwlen);
	bp++;
	BPF_SET_JUMP(bp, BPF_JMP + BPF_JEQ + BPF_K, htonl(ia->s_addr), 0, 1);
	bp++;
	BPF_SET_STMT(bp, BPF_RET + BPF_K, arp_len);
	bp++;

	/* If we didn't match sender, then we're only interested in
	 * ARP probes to us, so check the null host sender. */
	BPF_SET_JUMP(bp, BPF_JMP + BPF_JEQ + BPF_K, INADDR_ANY, 1, 0);
	bp++;
	BPF_SET_STMT(bp, BPF_RET + BPF_K, 0);
	bp++;

	/* Match target protocol address */
	BPF_SET_STMT(bp, BPF_LD + BPF_W + BPF_IND, (sizeof(struct arphdr) +
	    (size_t)(ifp->hwlen * 2) + sizeof(in_addr_t)));
	bp++;
	BPF_SET_JUMP(bp, BPF_JMP + BPF_JEQ + BPF_K, htonl(ia->s_addr), 0, 1);
	bp++;
	BPF_SET_STMT(bp, BPF_RET + BPF_K, arp_len);
	bp++;

	/* No match, drop it */
	BPF_SET_STMT(bp, BPF_RET + BPF_K, 0);
	bp++;

#ifdef BIOCSETWF
	if (!recv)
		return bpf_wattach(bpf->bpf_fd, buf, (unsigned int)(bp - buf));
#endif

	return bpf_attach(bpf->bpf_fd, buf, (unsigned int)(bp - buf));
}

int
bpf_arp(const struct bpf *bpf, const struct in_addr *ia)
{

#ifdef BIOCSETWF
	if (bpf_arp_rw(bpf, ia, true) == -1 ||
	    bpf_arp_rw(bpf, ia, false) == -1 ||
	    ioctl(bpf->bpf_fd, BIOCLOCK) == -1)
		return -1;
	return 0;
#else
	return bpf_arp_rw(bpf, ia, true);
#endif
}
#endif

#ifdef ARPHRD_NONE
static const struct bpf_insn bpf_bootp_none[] = {
};
#define BPF_BOOTP_NONE_LEN	__arraycount(bpf_bootp_none)
#endif

static const struct bpf_insn bpf_bootp_ether[] = {
	/* Make sure this is an IP packet. */
	BPF_STMT(BPF_LD + BPF_H + BPF_ABS,
	         offsetof(struct ether_header, ether_type)),
	BPF_JUMP(BPF_JMP + BPF_JEQ + BPF_K, ETHERTYPE_IP, 1, 0),
	BPF_STMT(BPF_RET + BPF_K, 0),

	/* Advance to the IP header. */
	BPF_STMT(BPF_LDX + BPF_K, sizeof(struct ether_header)),
};
#define BPF_BOOTP_ETHER_LEN	__arraycount(bpf_bootp_ether)

static const struct bpf_insn bpf_bootp_base[] = {
	/* Make sure it's an IPv4 packet. */
	BPF_STMT(BPF_LD + BPF_B + BPF_IND, 0),
	BPF_STMT(BPF_ALU + BPF_AND + BPF_K, 0xf0),
	BPF_JUMP(BPF_JMP + BPF_JEQ + BPF_K, 0x40, 1, 0),
	BPF_STMT(BPF_RET + BPF_K, 0),

	/* Make sure it's a UDP packet. */
	BPF_STMT(BPF_LD + BPF_B + BPF_IND, offsetof(struct ip, ip_p)),
	BPF_JUMP(BPF_JMP + BPF_JEQ + BPF_K, IPPROTO_UDP, 1, 0),
	BPF_STMT(BPF_RET + BPF_K, 0),

	/* Make sure this isn't a fragment. */
	BPF_STMT(BPF_LD + BPF_H + BPF_IND, offsetof(struct ip, ip_off)),
	BPF_JUMP(BPF_JMP + BPF_JSET + BPF_K, 0x1fff, 0, 1),
	BPF_STMT(BPF_RET + BPF_K, 0),

	/* Advance to the UDP header. */
	BPF_STMT(BPF_LD + BPF_B + BPF_IND, 0),
	BPF_STMT(BPF_ALU + BPF_AND + BPF_K, 0x0f),
	BPF_STMT(BPF_ALU + BPF_MUL + BPF_K, 4),
	BPF_STMT(BPF_ALU + BPF_ADD + BPF_X, 0),
	BPF_STMT(BPF_MISC + BPF_TAX, 0),
};
#define BPF_BOOTP_BASE_LEN	__arraycount(bpf_bootp_base)

static const struct bpf_insn bpf_bootp_read[] = {
	/* Make sure it's to the right port.
	 * RFC2131 makes no mention of enforcing a source port. */
	BPF_STMT(BPF_LD + BPF_H + BPF_IND, offsetof(struct udphdr, uh_dport)),
	BPF_JUMP(BPF_JMP + BPF_JEQ + BPF_K, BOOTPC, 1, 0),
	BPF_STMT(BPF_RET + BPF_K, 0),
};
#define BPF_BOOTP_READ_LEN	__arraycount(bpf_bootp_read)

#ifdef BIOCSETWF
static const struct bpf_insn bpf_bootp_write[] = {
	/* Make sure it's from and to the right port.
	 * RFC2131 makes no mention of encforcing a source port,
	 * but dhcpcd does enforce it for sending. */
	BPF_STMT(BPF_LD + BPF_W + BPF_IND, 0),
	BPF_JUMP(BPF_JMP + BPF_JEQ + BPF_K, (BOOTPC << 16) + BOOTPS, 1, 0),
	BPF_STMT(BPF_RET + BPF_K, 0),
};
#define BPF_BOOTP_WRITE_LEN	__arraycount(bpf_bootp_write)
#endif

#define BPF_BOOTP_CHADDR_LEN	((BOOTP_CHADDR_LEN / 4) * 3)
#define	BPF_BOOTP_XID_LEN	4 /* BOUND check is 4 instructions */

#define BPF_BOOTP_LEN		BPF_BOOTP_ETHER_LEN + \
				BPF_BOOTP_BASE_LEN + BPF_BOOTP_READ_LEN + \
				BPF_BOOTP_XID_LEN + BPF_BOOTP_CHADDR_LEN + 4

static int
bpf_bootp_rw(const struct bpf *bpf, bool read)
{
	struct bpf_insn buf[BPF_BOOTP_LEN + 1];
	struct bpf_insn *bp;

	bp = buf;
	/* Check frame header. */
	switch(bpf->bpf_ifp->hwtype) {
#ifdef ARPHRD_NONE
	case ARPHRD_NONE:
		memcpy(bp, bpf_bootp_none, sizeof(bpf_bootp_none));
		bp += BPF_BOOTP_NONE_LEN;
		break;
#endif
	case ARPHRD_ETHER:
		memcpy(bp, bpf_bootp_ether, sizeof(bpf_bootp_ether));
		bp += BPF_BOOTP_ETHER_LEN;
		break;
	default:
		errno = EINVAL;
		return -1;
	}

	/* Copy in the main filter. */
	memcpy(bp, bpf_bootp_base, sizeof(bpf_bootp_base));
	bp += BPF_BOOTP_BASE_LEN;

#ifdef BIOCSETWF
	if (!read) {
		memcpy(bp, bpf_bootp_write, sizeof(bpf_bootp_write));
		bp += BPF_BOOTP_WRITE_LEN;

		/* All passed, return the packet. */
		BPF_SET_STMT(bp, BPF_RET + BPF_K, BPF_WHOLEPACKET);
		bp++;

		return bpf_wattach(bpf->bpf_fd, buf, (unsigned int)(bp - buf));
	}
#else
	UNUSED(read);
#endif

	memcpy(bp, bpf_bootp_read, sizeof(bpf_bootp_read));
	bp += BPF_BOOTP_READ_LEN;

	/* All passed, return the packet. */
	BPF_SET_STMT(bp, BPF_RET + BPF_K, BPF_WHOLEPACKET);
	bp++;

	return bpf_attach(bpf->bpf_fd, buf, (unsigned int)(bp - buf));
}

int
bpf_bootp(const struct bpf *bpf, __unused const struct in_addr *ia)
{

#ifdef BIOCSETWF
	if (bpf_bootp_rw(bpf, true) == -1 ||
	    bpf_bootp_rw(bpf, false) == -1 ||
	    ioctl(bpf->bpf_fd, BIOCLOCK) == -1)
		return -1;
	return 0;
#else
#ifdef PRIVSEP
#if defined(__sun) /* Solaris cannot send via BPF. */
#elif defined(BIOCSETF)
#warning No BIOCSETWF support - a compromised BPF can be used as a raw socket
#else
#warning A compromised PF_PACKET socket can be used as a raw socket
#endif
#endif
	return bpf_bootp_rw(bpf, true);
#endif
}