/* $OpenBSD: bpf.c,v 1.63 2017/07/24 16:17:35 krw 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 #include #include #include "dhcp.h" #include "dhcpd.h" #include "log.h" int get_bpf_sock(char *name) { struct ifreq ifr; int sock; if ((sock = open("/dev/bpf", O_RDWR | O_CLOEXEC)) == -1) fatal("Can't open bpf"); /* Set the BPF device to point at this interface. */ strlcpy(ifr.ifr_name, name, IFNAMSIZ); if (ioctl(sock, BIOCSETIF, &ifr) == -1) fatal("Can't attach interface %s to /dev/bpf", name); return sock; } int get_udp_sock(int rdomain) { int sock, on = 1; /* * Use raw socket for unicast send. */ if ((sock = socket(AF_INET, SOCK_RAW, IPPROTO_UDP)) == -1) fatal("socket(SOCK_RAW)"); if (setsockopt(sock, IPPROTO_IP, IP_HDRINCL, &on, sizeof(on)) == -1) fatal("setsockopt(IP_HDRINCL)"); if (setsockopt(sock, IPPROTO_IP, SO_RTABLE, &rdomain, sizeof(rdomain)) == -1) fatal("setsockopt(SO_RTABLE)"); return sock; } /* * Packet filter program. * * N.B.: Changes to the filter program may require changes to the * constant offsets used in if_register_receive 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, (unsigned 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[] = { BPF_STMT(BPF_LD + BPF_B + BPF_IND, 14), BPF_JUMP(BPF_JMP + BPF_JEQ + BPF_K, (IPVERSION << 4) + 5, 0, 12), /* 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, 10), /* 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, 8), /* 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, 6, 0), /* patched */ /* 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, 68, 0, 3), /* 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, 67, 0, 1), /* If we passed all the tests, ask for the whole packet. */ BPF_STMT(BPF_RET+BPF_K, (unsigned 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); int configure_bpf_sock(int bfdesc) { struct bpf_version v; struct bpf_program p; int flag = 1, sz; /* Make sure the BPF version is in range. */ if (ioctl(bfdesc, 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 " "dhclient!"); /* * 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(bfdesc, BIOCIMMEDIATE, &flag) == -1) fatal("Can't set immediate mode on bpf device"); if (ioctl(bfdesc, BIOCSFILDROP, &flag) == -1) fatal("Can't set filter-drop mode on bpf device"); /* Get the required BPF buffer length from the kernel. */ if (ioctl(bfdesc, BIOCGBLEN, &sz) == -1) fatal("Can't get bpf buffer length"); /* 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. * * N.B.: changes to filter program may require changes to the * insn number(s) used below! */ dhcp_bpf_filter[8].k = LOCAL_PORT; if (ioctl(bfdesc, 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 (dhcp_bpf_wfilter[7].k == 0x1fff) dhcp_bpf_wfilter[7].k = htons(IP_MF|IP_OFFMASK); if (ioctl(bfdesc, BIOCSETWF, &p) == -1) fatal("Can't install write filter program"); if (ioctl(bfdesc, BIOCLOCK, NULL) == -1) fatal("Cannot lock bpf"); return sz; } ssize_t send_packet(struct interface_info *ifi, struct in_addr from, struct in_addr to) { struct iovec iov[4]; struct sockaddr_in dest; struct ether_header eh; struct ip ip; struct udphdr udp; struct msghdr msg; struct dhcp_packet *packet = &ifi->sent_packet; ssize_t result; int iovcnt = 0, len = ifi->sent_packet_length; memset(&dest, 0, sizeof(dest)); dest.sin_family = AF_INET; dest.sin_port = htons(REMOTE_PORT); dest.sin_addr.s_addr = to.s_addr; if (to.s_addr == INADDR_BROADCAST) { assemble_eh_header(ifi->hw_address, &eh); iov[0].iov_base = &eh; iov[0].iov_len = sizeof(eh); iovcnt++; } ip.ip_v = 4; ip.ip_hl = 5; ip.ip_tos = IPTOS_LOWDELAY; ip.ip_len = htons(sizeof(ip) + sizeof(udp) + len); ip.ip_id = 0; ip.ip_off = 0; ip.ip_ttl = 128; ip.ip_p = IPPROTO_UDP; ip.ip_sum = 0; ip.ip_src.s_addr = from.s_addr; ip.ip_dst.s_addr = to.s_addr; ip.ip_sum = wrapsum(checksum((unsigned char *)&ip, sizeof(ip), 0)); iov[iovcnt].iov_base = &ip; iov[iovcnt].iov_len = sizeof(ip); iovcnt++; udp.uh_sport = htons(LOCAL_PORT); udp.uh_dport = htons(REMOTE_PORT); udp.uh_ulen = htons(sizeof(udp) + len); udp.uh_sum = 0; udp.uh_sum = wrapsum(checksum((unsigned char *)&udp, sizeof(udp), checksum((unsigned char *)packet, len, checksum((unsigned char *)&ip.ip_src, 2 * sizeof(ip.ip_src), IPPROTO_UDP + (uint32_t)ntohs(udp.uh_ulen))))); iov[iovcnt].iov_base = &udp; iov[iovcnt].iov_len = sizeof(udp); iovcnt++; iov[iovcnt].iov_base = packet; iov[iovcnt].iov_len = len; iovcnt++; if (to.s_addr == INADDR_BROADCAST) { result = writev(ifi->bfdesc, iov, iovcnt); } else { memset(&msg, 0, sizeof(msg)); msg.msg_name = (struct sockaddr *)&dest; msg.msg_namelen = sizeof(dest); msg.msg_iov = iov; msg.msg_iovlen = iovcnt; result = sendmsg(ifi->ufdesc, &msg, 0); } if (result == -1) log_warn("send_packet"); return result ; } ssize_t receive_packet(struct interface_info *ifi, struct sockaddr_in *from, struct ether_addr *hfrom) { struct bpf_hdr hdr; struct dhcp_packet *packet = &ifi->recv_packet; int length = 0, offset = 0; /* * 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 (ifi->rbuf_offset >= ifi->rbuf_len) { length = read(ifi->bfdesc, ifi->rbuf, ifi->rbuf_max); if (length <= 0) return length ; ifi->rbuf_offset = 0; ifi->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 (ifi->rbuf_len - ifi->rbuf_offset < sizeof(hdr)) { ifi->rbuf_offset = ifi->rbuf_len; continue; } /* Copy out a bpf header. */ memcpy(&hdr, &ifi->rbuf[ifi->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 (ifi->rbuf_offset + hdr.bh_hdrlen + hdr.bh_caplen > ifi->rbuf_len) { ifi->rbuf_offset = ifi->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) { ifi->rbuf_offset = BPF_WORDALIGN( ifi->rbuf_offset + hdr.bh_hdrlen + hdr.bh_caplen); continue; } /* Skip over the BPF header. */ ifi->rbuf_offset += hdr.bh_hdrlen; /* Decode the physical header. */ offset = decode_hw_header(ifi->rbuf + ifi->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) { ifi->rbuf_offset = BPF_WORDALIGN( ifi->rbuf_offset + hdr.bh_caplen); continue; } ifi->rbuf_offset += offset; hdr.bh_caplen -= offset; /* Decode the IP and UDP headers. */ offset = decode_udp_ip_header(ifi->rbuf + ifi->rbuf_offset, hdr.bh_caplen, from); /* If the IP or UDP checksum was bad, skip the packet. */ if (offset < 0) { ifi->rbuf_offset = BPF_WORDALIGN( ifi->rbuf_offset + hdr.bh_caplen); continue; } ifi->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 > sizeof(*packet)) { ifi->rbuf_offset = BPF_WORDALIGN( ifi->rbuf_offset + hdr.bh_caplen); continue; } /* Copy out the data in the packet. */ memset(packet, DHO_END, sizeof(*packet)); memcpy(packet, ifi->rbuf + ifi->rbuf_offset, hdr.bh_caplen); ifi->rbuf_offset = BPF_WORDALIGN(ifi->rbuf_offset + hdr.bh_caplen); return hdr.bh_caplen ; } while (length == 0); return 0 ; }