/* $OpenBSD: bpf.c,v 1.2 2004/04/20 04:19:00 deraadt 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 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 "dhcpd.h" #include #include #include #include #include #include #include #define BPF_FORMAT "/dev/bpf%d" /* * 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(struct interface_info *info) { char filename[50]; int sock, b; /* Open a BPF device */ for (b = 0; 1; b++) { snprintf(filename, sizeof(filename), BPF_FORMAT, 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, info->ifp) < 0) error("Can't attach interface %s to bpf device %s: %m", info->name, filename); return (sock); } void if_register_send(struct interface_info *info) { /* * If we're using the bpf API for sending and receiving, we * don't need to register this interface twice. */ info->wfdesc = info->rfdesc; } /* * 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); void if_register_receive(struct interface_info *info) { struct bpf_version v; struct bpf_program p; int flag = 1, sz; /* Open a BPF device and hang it on this interface... */ info->rfdesc = if_register_bpf(info); /* Make sure the BPF version is in range... */ if (ioctl(info->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(info->rfdesc, BIOCIMMEDIATE, &flag) < 0) error("Can't set immediate mode on bpf device: %m"); /* Get the required BPF buffer length from the kernel. */ if (ioctl(info->rfdesc, BIOCGBLEN, &sz) < 0) error("Can't get bpf buffer length: %m"); info->rbuf_max = sz; info->rbuf = malloc(info->rbuf_max); if (!info->rbuf) error("Can't allocate %lu bytes for bpf input buffer.", (unsigned long)info->rbuf_max); info->rbuf_offset = 0; info->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(info->rfdesc, BIOCSETF, &p) < 0) error("Can't install packet filter program: %m"); } ssize_t send_packet(struct interface_info *interface, struct dhcp_packet *raw, size_t len, struct in_addr from, struct sockaddr_in *to, struct hardware *hto) { unsigned char buf[256]; struct iovec iov[2]; int result, bufp = 0; /* Assemble the headers... */ assemble_hw_header(interface, buf, &bufp, hto); assemble_udp_ip_header(interface, buf, &bufp, from.s_addr, to->sin_addr.s_addr, to->sin_port, (unsigned char *)raw, len); /* Fire it off */ iov[0].iov_base = (char *)buf; iov[0].iov_len = bufp; iov[1].iov_base = (char *)raw; iov[1].iov_len = len; result = writev(interface->wfdesc, iov, 2); if (result < 0) warn("send_packet: %m"); return (result); } ssize_t receive_packet(struct interface_info *interface, unsigned char *buf, size_t len, 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 (interface->rbuf_offset == interface->rbuf_len) { length = read(interface->rfdesc, interface->rbuf, interface->rbuf_max); if (length <= 0) return (length); interface->rbuf_offset = 0; interface->rbuf_len = 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 (interface->rbuf_len - interface->rbuf_offset < sizeof(hdr)) { interface->rbuf_offset = interface->rbuf_len; continue; } /* Copy out a bpf header... */ memcpy(&hdr, &interface->rbuf[interface->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 (interface->rbuf_offset + hdr.bh_hdrlen + hdr.bh_caplen > interface->rbuf_len) { interface->rbuf_offset = interface->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) { interface->rbuf_offset += hdr.bh_hdrlen = hdr.bh_caplen; continue; } /* Skip over the BPF header... */ interface->rbuf_offset += hdr.bh_hdrlen; /* Decode the physical header... */ offset = decode_hw_header(interface, interface->rbuf, interface->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) { interface->rbuf_offset += hdr.bh_caplen; continue; } interface->rbuf_offset += offset; hdr.bh_caplen -= offset; /* Decode the IP and UDP headers... */ offset = decode_udp_ip_header(interface, interface->rbuf, interface->rbuf_offset, from, NULL, hdr.bh_caplen); /* If the IP or UDP checksum was bad, skip the packet... */ if (offset < 0) { interface->rbuf_offset += hdr.bh_caplen; continue; } interface->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 > len) { interface->rbuf_offset += hdr.bh_caplen; continue; } /* Copy out the data in the packet... */ memcpy(buf, interface->rbuf + interface->rbuf_offset, hdr.bh_caplen); interface->rbuf_offset += hdr.bh_caplen; return (hdr.bh_caplen); } while (!length); return (0); }