105 lines
3.5 KiB
C
105 lines
3.5 KiB
C
/* vi: set sw=4 ts=4: */
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/*
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* clientsocket.c -- DHCP client socket creation
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*
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* udhcp client
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*
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* Russ Dill <Russ.Dill@asu.edu> July 2001
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*
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* This program is free software; you can redistribute it and/or modify
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* it under the terms of the GNU General Public License as published by
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* the Free Software Foundation; either version 2 of the License, or
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* (at your option) any later version.
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*
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* This program is distributed in the hope that it will be useful,
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* but WITHOUT ANY WARRANTY; without even the implied warranty of
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* MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the
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* GNU General Public License for more details.
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*
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* You should have received a copy of the GNU General Public License
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* along with this program; if not, write to the Free Software
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* Foundation, Inc., 675 Mass Ave, Cambridge, MA 02139, USA.
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*/
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#include <features.h>
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#if (defined(__GLIBC__) && __GLIBC__ >= 2 && __GLIBC_MINOR__ >= 1) || defined(_NEWLIB_VERSION)
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#include <netpacket/packet.h>
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#include <net/ethernet.h>
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#else
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#include <asm/types.h>
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#include <linux/if_packet.h>
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#include <linux/if_ether.h>
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#endif
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#include <linux/filter.h>
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#include "common.h"
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#define SERVER_AND_CLIENT_PORTS ((SERVER_PORT << 16) + CLIENT_PORT)
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int raw_socket(int ifindex)
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{
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int fd;
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struct sockaddr_ll sock;
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/*
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* Comment:
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*
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* I've selected not to see LL header, so BPF doesn't see it, too.
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* The filter may also pass non-IP and non-ARP packets, but we do
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* a more complete check when receiving the message in userspace.
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*
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* and filter shamelessly stolen from:
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*
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* http://www.flamewarmaster.de/software/dhcpclient/
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*
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* There are a few other interesting ideas on that page (look under
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* "Motivation"). Use of netlink events is most interesting. Think
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* of various network servers listening for events and reconfiguring.
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* That would obsolete sending HUP signals and/or make use of restarts.
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*
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* Copyright: 2006, 2007 Stefan Rompf <sux@loplof.de>.
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* License: GPL v2.
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*
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* TODO: make conditional?
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*/
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static const struct sock_filter filter_instr[] = {
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/* check for udp */
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BPF_STMT(BPF_LD|BPF_B|BPF_ABS, 9),
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BPF_JUMP(BPF_JMP|BPF_JEQ|BPF_K, IPPROTO_UDP, 2, 0), /* L5, L1, is UDP? */
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/* ugly check for arp on ethernet-like and IPv4 */
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BPF_STMT(BPF_LD|BPF_W|BPF_ABS, 2), /* L1: */
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BPF_JUMP(BPF_JMP|BPF_JEQ|BPF_K, 0x08000604, 3, 4), /* L3, L4 */
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/* skip IP header */
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BPF_STMT(BPF_LDX|BPF_B|BPF_MSH, 0), /* L5: */
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/* check udp source and destination ports */
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BPF_STMT(BPF_LD|BPF_W|BPF_IND, 0),
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BPF_JUMP(BPF_JMP|BPF_JEQ|BPF_K, SERVER_AND_CLIENT_PORTS, 0, 1), /* L3, L4 */
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/* returns */
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BPF_STMT(BPF_RET|BPF_K, ~0UL), /* L3: pass */
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BPF_STMT(BPF_RET|BPF_K, 0), /* L4: reject */
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};
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static const struct sock_fprog filter_prog = {
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.len = sizeof(filter_instr) / sizeof(filter_instr[0]),
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/* casting const away: */
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.filter = (struct sock_filter *) filter_instr,
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};
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DEBUG("opening raw socket on ifindex %d", ifindex);
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fd = xsocket(PF_PACKET, SOCK_DGRAM, htons(ETH_P_IP));
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DEBUG("got raw socket fd %d", fd);
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/* Ignoring error (kernel may lack support for this) */
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if (setsockopt(fd, SOL_SOCKET, SO_ATTACH_FILTER, &filter_prog,
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sizeof(filter_prog)) >= 0)
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DEBUG("attached filter to raw socket fd %d", fd);
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sock.sll_family = AF_PACKET;
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sock.sll_protocol = htons(ETH_P_IP);
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sock.sll_ifindex = ifindex;
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xbind(fd, (struct sockaddr *) &sock, sizeof(sock));
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DEBUG("bound to raw socket fd %d", fd);
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return fd;
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}
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