/*      $OpenBSD: bpf.c,v 1.20 2007/01/08 02:51:13 krw Exp $    */
/*      $DragonFly: src/sbin/dhclient/bpf.c,v 1.2 2008/11/05 14:08:41 sephe 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 <sys/ioctl.h>
#include <sys/uio.h>

#include <net/bpf.h>
#include <netinet/if_ether.h>
#include <netinet/in_systm.h>
#include <netinet/ip.h>
#include <netinet/udp.h>

#include "dhcpd.h"

/*
 * 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.  Try auto-clone first (newer kernels),
         * otherwise iterate (older kernels).
         */
        sock = open("/dev/bpf", O_RDWR, 0);
        if (sock < 0) {
                for (b = 0; 1; b++) {
                        snprintf(filename, sizeof(filename), "/dev/bpf%d", 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);
}