9b683f8da6
packets instead of allowing the protocol stack to pick a random source port. This fixes the behaviour where dhclient would never transition from RENEWING to BOUND without going through REBINDING in networks which are paranoid about DHCP spoofing, such as most mainstream cable-broadband ISP networks. Reviewed by: brooks Obtained from: OpenBSD (partly - I'm not convinced their solution can work) MFC after: 1 week (pending re approval)
412 lines
12 KiB
C
412 lines
12 KiB
C
/* $OpenBSD: bpf.c,v 1.13 2004/05/05 14:28:58 deraadt Exp $ */
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/* BPF socket interface code, originally contributed by Archie Cobbs. */
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/*
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* Copyright (c) 1995, 1996, 1998, 1999
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* The Internet Software Consortium. All rights reserved.
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*
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* Redistribution and use in source and binary forms, with or without
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* modification, are permitted provided that the following conditions
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* are met:
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*
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* 1. Redistributions of source code must retain the above copyright
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* notice, this list of conditions and the following disclaimer.
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* 2. Redistributions in binary form must reproduce the above copyright
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* notice, this list of conditions and the following disclaimer in the
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* documentation and/or other materials provided with the distribution.
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* 3. Neither the name of The Internet Software Consortium nor the names
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* of its contributors may be used to endorse or promote products derived
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* from this software without specific prior written permission.
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*
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* THIS SOFTWARE IS PROVIDED BY THE INTERNET SOFTWARE CONSORTIUM AND
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* CONTRIBUTORS ``AS IS'' AND ANY EXPRESS OR IMPLIED WARRANTIES,
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* INCLUDING, BUT NOT LIMITED TO, THE IMPLIED WARRANTIES OF
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* MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE ARE
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* DISCLAIMED. IN NO EVENT SHALL THE INTERNET SOFTWARE CONSORTIUM OR
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* CONTRIBUTORS BE LIABLE FOR ANY DIRECT, INDIRECT, INCIDENTAL,
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* SPECIAL, EXEMPLARY, OR CONSEQUENTIAL DAMAGES (INCLUDING, BUT NOT
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* LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS OR SERVICES; LOSS OF
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* USE, DATA, OR PROFITS; OR BUSINESS INTERRUPTION) HOWEVER CAUSED AND
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* ON ANY THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT LIABILITY,
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* OR TORT (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY OUT
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* OF THE USE OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF
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* SUCH DAMAGE.
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*
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* This software has been written for the Internet Software Consortium
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* by Ted Lemon <mellon@fugue.com> in cooperation with Vixie
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* Enterprises. To learn more about the Internet Software Consortium,
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* see ``http://www.vix.com/isc''. To learn more about Vixie
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* Enterprises, see ``http://www.vix.com''.
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*/
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#include <sys/cdefs.h>
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__FBSDID("$FreeBSD$");
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#include "dhcpd.h"
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#include <sys/ioctl.h>
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#include <sys/uio.h>
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#include <net/bpf.h>
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#include <netinet/in_systm.h>
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#include <netinet/ip.h>
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#include <netinet/udp.h>
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#include <netinet/if_ether.h>
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#define BPF_FORMAT "/dev/bpf%d"
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/*
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* Called by get_interface_list for each interface that's discovered.
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* Opens a packet filter for each interface and adds it to the select
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* mask.
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*/
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int
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if_register_bpf(struct interface_info *info)
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{
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char filename[50];
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int sock, b;
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/* Open a BPF device */
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for (b = 0; 1; b++) {
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snprintf(filename, sizeof(filename), BPF_FORMAT, b);
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sock = open(filename, O_RDWR, 0);
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if (sock < 0) {
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if (errno == EBUSY)
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continue;
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else
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error("Can't find free bpf: %m");
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} else
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break;
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}
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/* Set the BPF device to point at this interface. */
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if (ioctl(sock, BIOCSETIF, info->ifp) < 0)
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error("Can't attach interface %s to bpf device %s: %m",
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info->name, filename);
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return (sock);
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}
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void
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if_register_send(struct interface_info *info)
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{
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int sock, on = 1;
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/*
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* If we're using the bpf API for sending and receiving, we
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* don't need to register this interface twice.
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*/
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info->wfdesc = info->rfdesc;
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/*
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* Use raw socket for unicast send.
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*/
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if ((sock = socket(AF_INET, SOCK_RAW, IPPROTO_UDP)) == -1)
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error("socket(SOCK_RAW): %m");
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if (setsockopt(sock, IPPROTO_IP, IP_HDRINCL, &on,
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sizeof(on)) == -1)
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error("setsockopt(IP_HDRINCL): %m");
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info->ufdesc = sock;
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}
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/*
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* Packet filter program...
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*
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* XXX: Changes to the filter program may require changes to the
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* constant offsets used in if_register_send to patch the BPF program!
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*/
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struct bpf_insn dhcp_bpf_filter[] = {
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/* Make sure this is an IP packet... */
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BPF_STMT(BPF_LD + BPF_H + BPF_ABS, 12),
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BPF_JUMP(BPF_JMP + BPF_JEQ + BPF_K, ETHERTYPE_IP, 0, 8),
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/* Make sure it's a UDP packet... */
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BPF_STMT(BPF_LD + BPF_B + BPF_ABS, 23),
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BPF_JUMP(BPF_JMP + BPF_JEQ + BPF_K, IPPROTO_UDP, 0, 6),
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/* Make sure this isn't a fragment... */
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BPF_STMT(BPF_LD + BPF_H + BPF_ABS, 20),
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BPF_JUMP(BPF_JMP + BPF_JSET + BPF_K, 0x1fff, 4, 0),
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/* Get the IP header length... */
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BPF_STMT(BPF_LDX + BPF_B + BPF_MSH, 14),
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/* Make sure it's to the right port... */
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BPF_STMT(BPF_LD + BPF_H + BPF_IND, 16),
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BPF_JUMP(BPF_JMP + BPF_JEQ + BPF_K, 67, 0, 1), /* patch */
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/* If we passed all the tests, ask for the whole packet. */
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BPF_STMT(BPF_RET+BPF_K, (u_int)-1),
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/* Otherwise, drop it. */
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BPF_STMT(BPF_RET+BPF_K, 0),
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};
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int dhcp_bpf_filter_len = sizeof(dhcp_bpf_filter) / sizeof(struct bpf_insn);
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/*
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* Packet write filter program:
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* 'ip and udp and src port bootps and dst port (bootps or bootpc)'
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*/
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struct bpf_insn dhcp_bpf_wfilter[] = {
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BPF_STMT(BPF_LD + BPF_B + BPF_IND, 14),
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BPF_JUMP(BPF_JMP + BPF_JEQ + BPF_K, (IPVERSION << 4) + 5, 0, 12),
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/* Make sure this is an IP packet... */
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BPF_STMT(BPF_LD + BPF_H + BPF_ABS, 12),
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BPF_JUMP(BPF_JMP + BPF_JEQ + BPF_K, ETHERTYPE_IP, 0, 10),
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/* Make sure it's a UDP packet... */
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BPF_STMT(BPF_LD + BPF_B + BPF_ABS, 23),
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BPF_JUMP(BPF_JMP + BPF_JEQ + BPF_K, IPPROTO_UDP, 0, 8),
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/* Make sure this isn't a fragment... */
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BPF_STMT(BPF_LD + BPF_H + BPF_ABS, 20),
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BPF_JUMP(BPF_JMP + BPF_JSET + BPF_K, 0x1fff, 6, 0), /* patched */
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/* Get the IP header length... */
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BPF_STMT(BPF_LDX + BPF_B + BPF_MSH, 14),
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/* Make sure it's from the right port... */
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BPF_STMT(BPF_LD + BPF_H + BPF_IND, 14),
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BPF_JUMP(BPF_JMP + BPF_JEQ + BPF_K, 68, 0, 3),
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/* Make sure it is to the right ports ... */
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BPF_STMT(BPF_LD + BPF_H + BPF_IND, 16),
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BPF_JUMP(BPF_JMP + BPF_JEQ + BPF_K, 67, 0, 1),
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/* If we passed all the tests, ask for the whole packet. */
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BPF_STMT(BPF_RET+BPF_K, (u_int)-1),
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/* Otherwise, drop it. */
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BPF_STMT(BPF_RET+BPF_K, 0),
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};
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int dhcp_bpf_wfilter_len = sizeof(dhcp_bpf_wfilter) / sizeof(struct bpf_insn);
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void
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if_register_receive(struct interface_info *info)
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{
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struct bpf_version v;
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struct bpf_program p;
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int flag = 1, sz;
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/* Open a BPF device and hang it on this interface... */
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info->rfdesc = if_register_bpf(info);
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/* Make sure the BPF version is in range... */
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if (ioctl(info->rfdesc, BIOCVERSION, &v) < 0)
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error("Can't get BPF version: %m");
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if (v.bv_major != BPF_MAJOR_VERSION ||
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v.bv_minor < BPF_MINOR_VERSION)
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error("Kernel BPF version out of range - recompile dhcpd!");
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/*
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* Set immediate mode so that reads return as soon as a packet
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* comes in, rather than waiting for the input buffer to fill
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* with packets.
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*/
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if (ioctl(info->rfdesc, BIOCIMMEDIATE, &flag) < 0)
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error("Can't set immediate mode on bpf device: %m");
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/* Get the required BPF buffer length from the kernel. */
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if (ioctl(info->rfdesc, BIOCGBLEN, &sz) < 0)
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error("Can't get bpf buffer length: %m");
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info->rbuf_max = sz;
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info->rbuf = malloc(info->rbuf_max);
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if (!info->rbuf)
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error("Can't allocate %lu bytes for bpf input buffer.",
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(unsigned long)info->rbuf_max);
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info->rbuf_offset = 0;
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info->rbuf_len = 0;
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/* Set up the bpf filter program structure. */
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p.bf_len = dhcp_bpf_filter_len;
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p.bf_insns = dhcp_bpf_filter;
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/* Patch the server port into the BPF program...
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*
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* XXX: changes to filter program may require changes to the
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* insn number(s) used below!
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*/
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dhcp_bpf_filter[8].k = LOCAL_PORT;
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if (ioctl(info->rfdesc, BIOCSETF, &p) < 0)
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error("Can't install packet filter program: %m");
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/* Set up the bpf write filter program structure. */
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p.bf_len = dhcp_bpf_wfilter_len;
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p.bf_insns = dhcp_bpf_wfilter;
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if (dhcp_bpf_wfilter[7].k == 0x1fff)
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dhcp_bpf_wfilter[7].k = htons(IP_MF|IP_OFFMASK);
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if (ioctl(info->rfdesc, BIOCSETWF, &p) < 0)
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error("Can't install write filter program: %m");
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if (ioctl(info->rfdesc, BIOCLOCK, NULL) < 0)
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error("Cannot lock bpf");
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}
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ssize_t
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send_packet(struct interface_info *interface, struct dhcp_packet *raw,
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size_t len, struct in_addr from, struct sockaddr_in *to,
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struct hardware *hto)
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{
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unsigned char buf[256];
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struct iovec iov[2];
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struct msghdr msg;
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int result, bufp = 0;
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/* Assemble the headers... */
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if (to->sin_addr.s_addr == INADDR_BROADCAST)
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assemble_hw_header(interface, buf, &bufp, hto);
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assemble_udp_ip_header(buf, &bufp, from.s_addr,
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to->sin_addr.s_addr, to->sin_port, (unsigned char *)raw, len);
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iov[0].iov_base = (char *)buf;
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iov[0].iov_len = bufp;
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iov[1].iov_base = (char *)raw;
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iov[1].iov_len = len;
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/* Fire it off */
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if (to->sin_addr.s_addr == INADDR_BROADCAST)
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result = writev(interface->wfdesc, iov, 2);
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else {
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memset(&msg, 0, sizeof(msg));
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msg.msg_name = (struct sockaddr *)to;
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msg.msg_namelen = sizeof(*to);
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msg.msg_iov = iov;
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msg.msg_iovlen = 2;
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result = sendmsg(interface->ufdesc, &msg, 0);
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}
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if (result < 0)
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warning("send_packet: %m");
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return (result);
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}
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ssize_t
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receive_packet(struct interface_info *interface, unsigned char *buf,
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size_t len, struct sockaddr_in *from, struct hardware *hfrom)
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{
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int length = 0, offset = 0;
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struct bpf_hdr hdr;
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/*
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* All this complexity is because BPF doesn't guarantee that
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* only one packet will be returned at a time. We're getting
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* what we deserve, though - this is a terrible abuse of the BPF
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* interface. Sigh.
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*/
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/* Process packets until we get one we can return or until we've
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* done a read and gotten nothing we can return...
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*/
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do {
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/* If the buffer is empty, fill it. */
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if (interface->rbuf_offset >= interface->rbuf_len) {
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length = read(interface->rfdesc, interface->rbuf,
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interface->rbuf_max);
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if (length <= 0)
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return (length);
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interface->rbuf_offset = 0;
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interface->rbuf_len = length;
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}
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/*
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* If there isn't room for a whole bpf header, something
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* went wrong, but we'll ignore it and hope it goes
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* away... XXX
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*/
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if (interface->rbuf_len - interface->rbuf_offset <
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sizeof(hdr)) {
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interface->rbuf_offset = interface->rbuf_len;
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continue;
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}
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/* Copy out a bpf header... */
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memcpy(&hdr, &interface->rbuf[interface->rbuf_offset],
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sizeof(hdr));
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/*
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* If the bpf header plus data doesn't fit in what's
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* left of the buffer, stick head in sand yet again...
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*/
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if (interface->rbuf_offset + hdr.bh_hdrlen + hdr.bh_caplen >
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interface->rbuf_len) {
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interface->rbuf_offset = interface->rbuf_len;
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continue;
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}
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/* Skip over the BPF header... */
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interface->rbuf_offset += hdr.bh_hdrlen;
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/*
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* If the captured data wasn't the whole packet, or if
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* the packet won't fit in the input buffer, all we can
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* do is drop it.
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*/
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if (hdr.bh_caplen != hdr.bh_datalen) {
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interface->rbuf_offset =
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BPF_WORDALIGN(interface->rbuf_offset +
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hdr.bh_caplen);
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continue;
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}
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/* Decode the physical header... */
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offset = decode_hw_header(interface->rbuf,
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interface->rbuf_offset, hfrom);
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/*
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* If a physical layer checksum failed (dunno of any
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* physical layer that supports this, but WTH), skip
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* this packet.
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*/
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if (offset < 0) {
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interface->rbuf_offset =
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BPF_WORDALIGN(interface->rbuf_offset +
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hdr.bh_caplen);
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continue;
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}
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interface->rbuf_offset += offset;
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hdr.bh_caplen -= offset;
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/* Decode the IP and UDP headers... */
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offset = decode_udp_ip_header(interface->rbuf,
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interface->rbuf_offset, from, NULL, hdr.bh_caplen);
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/* If the IP or UDP checksum was bad, skip the packet... */
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if (offset < 0) {
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interface->rbuf_offset =
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BPF_WORDALIGN(interface->rbuf_offset +
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hdr.bh_caplen);
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continue;
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}
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interface->rbuf_offset += offset;
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hdr.bh_caplen -= offset;
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/*
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* If there's not enough room to stash the packet data,
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* we have to skip it (this shouldn't happen in real
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* life, though).
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*/
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if (hdr.bh_caplen > len) {
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interface->rbuf_offset =
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BPF_WORDALIGN(interface->rbuf_offset +
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hdr.bh_caplen);
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continue;
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}
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/* Copy out the data in the packet... */
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memcpy(buf, interface->rbuf + interface->rbuf_offset,
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hdr.bh_caplen);
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interface->rbuf_offset =
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BPF_WORDALIGN(interface->rbuf_offset +
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hdr.bh_caplen);
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return (hdr.bh_caplen);
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} while (!length);
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return (0);
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}
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