ndhc/ndhc/socket.c

/* socket.c - raw and kernel socket creation functions
 * Time-stamp: <2011-03-30 23:47:03 nk>
 *
 * (c) 2004-2011 Nicholas J. Kain <njkain at gmail dot com>
 * Kernel BPF filter is (c) 2006, 2007 Stefan Rompf <sux@loplof.de>.
 *
 * This program is free software; you can redistribute it and/or modify
 * it under the terms of the GNU General Public License as published by
 * the Free Software Foundation; either version 2 of the License, or
 * (at your option) any later version.
 *
 * This program is distributed in the hope that it will be useful,
 * but WITHOUT ANY WARRANTY; without even the implied warranty of
 * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
 * GNU General Public License for more details.
 *
 * You should have received a copy of the GNU General Public License
 * along with this program; if not, write to the Free Software
 * Foundation, Inc., 675 Mass Ave, Cambridge, MA 02139, USA.
 */

#include <sys/types.h>
#include <sys/socket.h>
#include <netinet/in.h>
#include <unistd.h>
#include <fcntl.h>
#include <string.h>
#include <arpa/inet.h>
#include <net/if.h>
#include <errno.h>
#include <features.h>
#include <netpacket/packet.h>
#include <net/ethernet.h>
#include <linux/filter.h>
#include "log.h"
#include "strl.h"

int set_sock_nonblock(int fd)
{
    int ret = 0, flags;
    flags = fcntl(fd, F_GETFL);
    ret = fcntl(fd, F_SETFL, flags | O_NONBLOCK);
    return ret;
}

/* Returns fd of new listen socket bound to @ip:@port on interface @inf
 * on success, or -1 on failure. */
int listen_socket(unsigned int ip, int port, char *inf)
{
    struct ifreq interface;
    int fd;
    struct sockaddr_in addr;
    int opt = 1;

    log_line("Opening listen socket on 0x%08x:%d %s", ip, port, inf);
    if ((fd = socket(PF_INET, SOCK_DGRAM, IPPROTO_UDP)) < 0) {
        log_error("listen_socket: socket failed: %s", strerror(errno));
        goto out;
    }

    if (setsockopt(fd, SOL_SOCKET, SO_REUSEADDR, &opt, sizeof opt) == -1)
        goto out_fd;
    if (setsockopt(fd, SOL_SOCKET, SO_BROADCAST, &opt, sizeof opt) == -1)
        goto out_fd;

    /* Restrict operations to the physical device @inf */
    strlcpy(interface.ifr_ifrn.ifrn_name, inf, IFNAMSIZ);
    if (setsockopt(fd, SOL_SOCKET, SO_BINDTODEVICE,
                   &interface, sizeof interface) < 0)
        goto out_fd;

    set_sock_nonblock(fd);

    memset(&addr, 0, sizeof addr);
    addr.sin_family = AF_INET;
    addr.sin_port = htons(port);
    addr.sin_addr.s_addr = ip;
    if (bind(fd, (struct sockaddr *)&addr, sizeof(struct sockaddr)) == -1)
        goto out_fd;

    return fd;
  out_fd:
    close(fd);
  out:
    return -1;
}

int raw_socket(int ifindex)
{
    int fd;
    struct sockaddr_ll sock;

    /*
     * Comment:
     *   I've selected not to see LL header, so BPF doesn't see it, too.
     *   The filter may also pass non-IP and non-ARP packets, but we do
     *   a more complete check when receiving the message in userspace.
     * and filter shamelessly stolen from:
     *   http://www.flamewarmaster.de/software/dhcpclient/
     *
     *  Copyright: 2006, 2007 Stefan Rompf <sux@loplof.de>.
     *  License: GPL v2.
     */
#define SERVER_AND_CLIENT_PORTS  ((67 << 16) + 68)
    static const struct sock_filter filter_instr[] = {
        /* check for udp */
        BPF_STMT(BPF_LD|BPF_B|BPF_ABS, 9),
        BPF_JUMP(BPF_JMP|BPF_JEQ|BPF_K, IPPROTO_UDP, 2, 0),     /* L5, L1, is UDP? */
        /* ugly check for arp on ethernet-like and IPv4 */
        BPF_STMT(BPF_LD|BPF_W|BPF_ABS, 2),                      /* L1: */
        BPF_JUMP(BPF_JMP|BPF_JEQ|BPF_K, 0x08000604, 3, 4),      /* L3, L4 */
        /* skip IP header */
        BPF_STMT(BPF_LDX|BPF_B|BPF_MSH, 0),                     /* L5: */
        /* check udp source and destination ports */
        BPF_STMT(BPF_LD|BPF_W|BPF_IND, 0),
        BPF_JUMP(BPF_JMP|BPF_JEQ|BPF_K, SERVER_AND_CLIENT_PORTS, 0, 1),/* L3, L4 */
        /* returns */
        BPF_STMT(BPF_RET|BPF_K, 0x0fffffff ),                   /* L3: pass */
        BPF_STMT(BPF_RET|BPF_K, 0),                             /* L4: reject */
    };
    static const struct sock_fprog filter_prog = {
        .len = sizeof(filter_instr) / sizeof(filter_instr[0]),
        /* casting const away: */
        .filter = (struct sock_filter *) filter_instr,
    };

    memset(&sock, 0, sizeof sock);
    log_line("Opening raw socket on ifindex %d", ifindex);
    if ((fd = socket(PF_PACKET, SOCK_DGRAM, htons(ETH_P_IP))) < 0) {
        log_error("socket call failed: %s", strerror(errno));
        return -1;
    }

    /* Ignoring error (kernel may lack support for this) */
    if (setsockopt(fd, SOL_SOCKET, SO_ATTACH_FILTER, &filter_prog,
                   sizeof filter_prog) >= 0)
        log_line("Attached filter to raw socket fd %d", fd);

    set_sock_nonblock(fd);

    sock.sll_family = AF_PACKET;
    sock.sll_protocol = htons(ETH_P_IP);
    sock.sll_ifindex = ifindex;
    if (bind(fd, (struct sockaddr *)&sock, sizeof(sock)) < 0) {
        log_error("bind call failed: %s", strerror(errno));
        close(fd);
        return -1;
    }

    return fd;
}