/* $OpenBSD: bpf.c,v 1.19 2017/04/19 05:36:12 natano 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 #include #include #include #include #include #include #include #include #include #include #include #include #include #include "dhcp.h" #include "tree.h" #include "dhcpd.h" #include "log.h" ssize_t send_packet (struct interface_info *, struct dhcp_packet *, size_t, struct in_addr, struct sockaddr_in *, struct hardware *); /* * 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) { int sock; if ((sock = open("/dev/bpf", O_RDWR)) == -1) fatal("Can't open bpf device"); /* Set the BPF device to point at this interface. */ if (ioctl(sock, BIOCSETIF, info->ifp) == -1) fatal("Can't attach interface %s to bpf device", info->name); info->send_packet = send_packet; 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 read filter program: 'ip and udp and dst port bootps' */ 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, SERVER_PORT, 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_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[] = { /* 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, 11), /* 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, 9), /* 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, 7, 0), /* 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, SERVER_PORT, 0, 4), /* 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, CLIENT_PORT, 1, 0), BPF_JUMP(BPF_JMP + BPF_JEQ + BPF_K, SERVER_PORT, 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(struct interface_info *info) { struct bpf_version v; struct bpf_program p; int flag = 1, sz, cmplt = 0; /* 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) == -1) fatal("Can't get BPF version"); if (v.bv_major != BPF_MAJOR_VERSION || v.bv_minor < BPF_MINOR_VERSION) fatalx("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) == -1) fatal("Can't set immediate mode on bpf device"); if (ioctl(info->rfdesc, BIOCSFILDROP, &flag) == -1) fatal("Can't set filter-drop mode on bpf device"); /* make sure kernel fills in the source ethernet address */ if (ioctl(info->rfdesc, BIOCSHDRCMPLT, &cmplt) == -1) fatal("Can't set header complete flag on bpf device"); /* Get the required BPF buffer length from the kernel. */ if (ioctl(info->rfdesc, BIOCGBLEN, &sz) == -1) fatal("Can't get bpf buffer length"); info->rbuf_max = sz; info->rbuf = malloc(info->rbuf_max); if (!info->rbuf) fatalx("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; if (ioctl(info->rfdesc, BIOCSETF, &p) == -1) fatal("Can't install packet filter program"); /* Set up the bpf write filter program structure. */ p.bf_len = dhcp_bpf_wfilter_len; p.bf_insns = dhcp_bpf_wfilter; if (ioctl(info->rfdesc, BIOCSETWF, &p) == -1) fatal("Can't install write filter program"); /* make sure these settings cannot be changed after dropping privs */ if (ioctl(info->rfdesc, BIOCLOCK) == -1) fatal("Failed to lock bpf descriptor"); } 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]; ssize_t result; int 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 == -1) log_warn("send_packet"); 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 = BPF_WORDALIGN( 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->rbuf + interface->rbuf_offset, hdr.bh_caplen, 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 = BPF_WORDALIGN( 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->rbuf + interface->rbuf_offset, hdr.bh_caplen, from); /* If the IP or UDP checksum was bad, skip the packet... */ if (offset < 0) { interface->rbuf_offset = BPF_WORDALIGN( 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 = BPF_WORDALIGN( 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 = BPF_WORDALIGN(interface->rbuf_offset + hdr.bh_caplen); return (hdr.bh_caplen); } while (!length); return (0); }