/* SPDX-License-Identifier: BSD-2-Clause */
/*
 * dhcpcd: BPF arp and bootp filtering
 * Copyright (c) 2006-2020 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 <paths.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"

#define	ARP_ADDRS_MAX	3

/* 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 char *frame)
{

	switch (ifp->hwtype) {
	case ARPHRD_ETHER:
		return memcmp(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";

int
bpf_open(struct interface *ifp, int (*filter)(struct interface *, int))
{
	struct ipv4_state *state;
	int fd = -1;
	struct ifreq ifr;
	int ibuf_len = 0;
	size_t buf_len;
	struct bpf_version pv;
#ifdef BIOCIMMEDIATE
	unsigned int flags;
#endif
#ifndef O_CLOEXEC
	int fd_opts;
#endif

#ifdef _PATH_BPF
	fd = open(_PATH_BPF, O_RDWR | O_NONBLOCK
#ifdef O_CLOEXEC
		| O_CLOEXEC
#endif
	);
#else
	char device[32];
	int n = 0;

	do {
		snprintf(device, sizeof(device), "/dev/bpf%d", n++);
		fd = open(device, O_RDWR | O_NONBLOCK
#ifdef O_CLOEXEC
				| O_CLOEXEC
#endif
		);
	} while (fd == -1 && errno == EBUSY);
#endif

	if (fd == -1)
		return -1;

#ifndef O_CLOEXEC
	if ((fd_opts = fcntl(fd, F_GETFD)) == -1 ||
	    fcntl(fd, F_SETFD, fd_opts | FD_CLOEXEC) == -1) {
		close(fd);
		return -1;
	}
#endif

	memset(&pv, 0, sizeof(pv));
	if (ioctl(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;
	}

	if (filter(ifp, fd) != 0)
		goto eexit;

	memset(&ifr, 0, sizeof(ifr));
	strlcpy(ifr.ifr_name, ifp->name, sizeof(ifr.ifr_name));
	if (ioctl(fd, BIOCSETIF, &ifr) == -1)
		goto eexit;

	/* Get the required BPF buffer length from the kernel. */
	if (ioctl(fd, BIOCGBLEN, &ibuf_len) == -1)
		goto eexit;
	buf_len = (size_t)ibuf_len;
	state = ipv4_getstate(ifp);
	if (state == NULL)
		goto eexit;
	if (state->buffer_size != buf_len) {
		void *nb;

		if ((nb = realloc(state->buffer, buf_len)) == NULL)
			goto eexit;
		state->buffer = nb;
		state->buffer_size = buf_len;
	}

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

	return fd;

eexit:
	close(fd);
	return -1;
}

/* 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 interface *ifp, int fd, void *data, size_t len,
    unsigned int *flags)
{
	ssize_t bytes;
	struct ipv4_state *state = IPV4_STATE(ifp);

	struct bpf_hdr packet;
	const char *payload;

	*flags &= ~BPF_EOF;
	for (;;) {
		if (state->buffer_len == 0) {
			bytes = read(fd, state->buffer, state->buffer_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(fd, 0, SEEK_SET);
				continue;
			}
#endif
			if (bytes == -1 || bytes == 0)
				return bytes;
			state->buffer_len = (size_t)bytes;
			state->buffer_pos = 0;
		}
		bytes = -1;
		memcpy(&packet, state->buffer + state->buffer_pos,
		    sizeof(packet));
		if (state->buffer_pos + packet.bh_caplen + packet.bh_hdrlen >
		    state->buffer_len)
			goto next; /* Packet beyond buffer, drop. */
		payload = state->buffer + state->buffer_pos + packet.bh_hdrlen;
		if (bpf_frame_bcast(ifp, payload) == 0)
			*flags |= BPF_BCAST;
		else
			*flags &= ~BPF_BCAST;
		if (packet.bh_caplen > len)
			bytes = (ssize_t)len;
		else
			bytes = (ssize_t)packet.bh_caplen;
		memcpy(data, payload, (size_t)bytes);
next:
		state->buffer_pos += BPF_WORDALIGN(packet.bh_hdrlen +
		    packet.bh_caplen);
		if (state->buffer_pos >= state->buffer_len) {
			state->buffer_len = state->buffer_pos = 0;
			*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 interface *ifp, int fd, uint16_t protocol,
    const void *data, size_t len)
{
	struct iovec iov[2];
	struct ether_header eh;

	switch(ifp->hwtype) {
	case ARPHRD_ETHER:
		memset(&eh.ether_dhost, 0xff, sizeof(eh.ether_dhost));
		memcpy(&eh.ether_shost, 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(fd, iov, 2);
}
#endif

int
bpf_close(struct interface *ifp, int fd)
{
	struct ipv4_state *state = IPV4_STATE(ifp);

	/* Rewind the buffer on closing. */
	state->buffer_len = state->buffer_pos = 0;
	return close(fd);
}

#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)

#define BPF_ARP_ADDRS_LEN	1 + (ARP_ADDRS_MAX * 2) + 3 + \
				(ARP_ADDRS_MAX * 2) + 1

#define BPF_ARP_LEN		BPF_ARP_ETHER_LEN + BPF_ARP_FILTER_LEN

int
bpf_arp(struct interface *ifp, int fd)
{
	struct bpf_insn bpf[BPF_ARP_LEN + 1];
	struct bpf_insn *bp;
	uint16_t arp_len;

	if (fd == -1)
		return 0;

	bp = bpf;
	/* 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;

	/* Past the filer so return the packet. */
	BPF_SET_STMT(bp, BPF_RET + BPF_K, arp_len);
	bp++;

	if (bpf_attach(fd, bpf, (unsigned int)(bp - bpf)) == -1)
		return -1;

#ifdef BIOCSETWF
	if (bpf_wattach(fd, bpf, (unsigned int)(bp - bpf)) == -1 ||
	    ioctl(fd, BIOCLOCK) == -1)
		return -1;
#endif

	return 0;
}
#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)

#define BOOTP_MIN_SIZE		sizeof(struct ip) + sizeof(struct udphdr) + \
				sizeof(struct bootp)

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 from and to the right port. */
	BPF_STMT(BPF_LD + BPF_W + BPF_IND, 0),
	BPF_JUMP(BPF_JMP + BPF_JEQ + BPF_K, (BOOTPS << 16) + 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. */
	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(struct interface *ifp, int fd, bool read)
{
	struct bpf_insn bpf[BPF_BOOTP_LEN + 1];
	struct bpf_insn *bp;

	if (fd == -1)
		return 0;

	bp = bpf;
	/* Check frame header. */
	switch(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(fd, bpf, (unsigned int)(bp - bpf));
	}
#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(fd, bpf, (unsigned int)(bp - bpf));
}

int
bpf_bootp(struct interface *ifp, int fd)
{

#ifdef BIOCSETWF
	if (bpf_bootp_rw(ifp, fd, true) == -1 ||
	    bpf_bootp_rw(ifp, fd, false) == -1 ||
	    ioctl(fd, BIOCLOCK) == -1)
		return -1;
	return 0;
#else
	return bpf_bootp_rw(ifp, fd, true);
#endif
}