--- /dev/null
- iface.resizeReadBuffer(buf_len);
+// Copyright (C) 2014 Internet Systems Consortium, Inc. ("ISC")
+//
+// Permission to use, copy, modify, and/or distribute this software for any
+// purpose with or without fee is hereby granted, provided that the above
+// copyright notice and this permission notice appear in all copies.
+//
+// THE SOFTWARE IS PROVIDED "AS IS" AND ISC DISCLAIMS ALL WARRANTIES WITH
+// REGARD TO THIS SOFTWARE INCLUDING ALL IMPLIED WARRANTIES OF MERCHANTABILITY
+// AND FITNESS. IN NO EVENT SHALL ISC BE LIABLE FOR ANY SPECIAL, DIRECT,
+// INDIRECT, OR CONSEQUENTIAL DAMAGES OR ANY DAMAGES WHATSOEVER RESULTING FROM
+// LOSS OF USE, DATA OR PROFITS, WHETHER IN AN ACTION OF CONTRACT, NEGLIGENCE
+// OR OTHER TORTIOUS ACTION, ARISING OUT OF OR IN CONNECTION WITH THE USE OR
+// PERFORMANCE OF THIS SOFTWARE.
+
+#include <config.h>
+#include <dhcp/dhcp4.h>
+#include <dhcp/iface_mgr.h>
+#include <dhcp/pkt4.h>
+#include <dhcp/pkt_filter_bpf.h>
+#include <dhcp/protocol_util.h>
+#include <exceptions/exceptions.h>
+#include <algorithm>
+#include <net/bpf.h>
+#include <netinet/if_ether.h>
+
+namespace {
+
+using namespace isc::dhcp;
+
+/// @brief Maximum number of attempts to open BPF device.
+const unsigned int MAX_BPF_OPEN_ATTEMPTS = 100;
+
+/// @brief Length of the header containing the address family for the packet
+/// received on local loopback interface.
+const unsigned int BPF_LOCAL_LOOPBACK_HEADER_LEN = 4;
+
+/// The following structure defines a Berkely Packet Filter program to perform
+/// packet filtering. The program operates on Ethernet packets. To help with
+/// interpretation of the program, for the types of Ethernet packets we are
+/// interested in, the header layout is:
+///
+/// 6 bytes Destination Ethernet Address
+/// 6 bytes Source Ethernet Address
+/// 2 bytes Ethernet packet type
+///
+/// 20 bytes Fixed part of IP header
+/// variable Variable part of IP header
+///
+/// 2 bytes UDP Source port
+/// 2 bytes UDP destination port
+/// 4 bytes Rest of UDP header
+///
+/// @todo We may want to extend the filter to receive packets sent
+/// to the particular IP address assigned to the interface or
+/// broadcast address.
+struct bpf_insn ethernet_ip_udp_filter [] = {
+ // Make sure this is an IP packet: check the half-word (two bytes)
+ // at offset 12 in the packet (the Ethernet packet type). If it
+ // is, advance to the next instruction. If not, advance 8
+ // instructions (which takes execution to the last instruction in
+ // the sequence: "drop it").
+ BPF_STMT(BPF_LD + BPF_H + BPF_ABS, ETHERNET_PACKET_TYPE_OFFSET),
+ BPF_JUMP(BPF_JMP + BPF_JEQ + BPF_K, ETHERTYPE_IP, 0, 8),
+
+ // Make sure it's a UDP packet. The IP protocol is at offset
+ // 9 in the IP header so, adding the Ethernet packet header size
+ // of 14 bytes gives an absolute byte offset in the packet of 23.
+ BPF_STMT(BPF_LD + BPF_B + BPF_ABS,
+ ETHERNET_HEADER_LEN + IP_PROTO_TYPE_OFFSET),
+ BPF_JUMP(BPF_JMP + BPF_JEQ + BPF_K, IPPROTO_UDP, 0, 6),
+
+ // Make sure this isn't a fragment by checking that the fragment
+ // offset field in the IP header is zero. This field is the
+ // least-significant 13 bits in the bytes at offsets 6 and 7 in
+ // the IP header, so the half-word at offset 20 (6 + size of
+ // Ethernet header) is loaded and an appropriate mask applied.
+ BPF_STMT(BPF_LD + BPF_H + BPF_ABS, ETHERNET_HEADER_LEN + IP_FLAGS_OFFSET),
+ BPF_JUMP(BPF_JMP + BPF_JSET + BPF_K, 0x1fff, 4, 0),
+
+ // Get the IP header length. This is achieved by the following
+ // (special) instruction that, given the offset of the start
+ // of the IP header (offset 14) loads the IP header length.
+ BPF_STMT(BPF_LDX + BPF_B + BPF_MSH, ETHERNET_HEADER_LEN),
+
+ // Make sure it's to the right port. The following instruction
+ // adds the previously extracted IP header length to the given
+ // offset to locate the correct byte. The given offset of 16
+ // comprises the length of the Ethernet header (14) plus the offset
+ // of the UDP destination port (2) within the UDP header.
+ BPF_STMT(BPF_LD + BPF_H + BPF_IND, ETHERNET_HEADER_LEN + UDP_DEST_PORT),
+ // The following instruction tests against the default DHCP server port,
+ // but the action port is actually set in PktFilterBPF::openSocket().
+ // N.B. The code in that method assumes that this instruction is at
+ // offset 8 in the program. If this is changed, openSocket() must be
+ // updated.
+ BPF_JUMP(BPF_JMP + BPF_JEQ + BPF_K, DHCP4_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),
+};
+
+/// The following structure defines a BPF program to perform packet filtering
+/// on local loopback interface. The packets received on this interface do not
+/// contain the regular link-layer header, but rather a 4-byte long pseudo
+/// header containing the address family. The reminder of the packet contains
+/// IP header, UDP header and a DHCP message.
+struct bpf_insn loopback_ip_udp_filter [] = {
+ // Make sure this is an IP packet. The pseudo header comprises a 4-byte
+ // long value identifying the address family, which should be set to
+ // AF_INET. The default value used here (0xFFFFFFFF) must be overriden
+ // with htonl(AF_INET) from within the openSocket function.
+ BPF_STMT(BPF_LD + BPF_W + BPF_ABS, 0),
+ BPF_JUMP(BPF_JMP + BPF_JEQ + BPF_K, 0xFFFFFFFF, 0, 8),
+
+ // Make sure it's a UDP packet. The IP protocol is at offset
+ // 9 in the IP header so, adding the pseudo header size 4 bytes
+ // gives an absolute byte offset in the packet of 13.
+ BPF_STMT(BPF_LD + BPF_B + BPF_ABS,
+ BPF_LOCAL_LOOPBACK_HEADER_LEN + IP_PROTO_TYPE_OFFSET),
+ BPF_JUMP(BPF_JMP + BPF_JEQ + BPF_K, IPPROTO_UDP, 0, 6),
+
+ // Make sure this isn't a fragment by checking that the fragment
+ // offset field in the IP header is zero. This field is the
+ // least-significant 13 bits in the bytes at offsets 6 and 7 in
+ // the IP header, so the half-word at offset 10 (6 + size of
+ // pseudo header) is loaded and an appropriate mask applied.
+ BPF_STMT(BPF_LD + BPF_H + BPF_ABS,
+ BPF_LOCAL_LOOPBACK_HEADER_LEN + IP_FLAGS_OFFSET),
+ BPF_JUMP(BPF_JMP + BPF_JSET + BPF_K, 0x1fff, 4, 0),
+
+ // Get the IP header length. This is achieved by the following
+ // (special) instruction that, given the offset of the start
+ // of the IP header (offset 4) loads the IP header length.
+ BPF_STMT(BPF_LDX + BPF_B + BPF_MSH, BPF_LOCAL_LOOPBACK_HEADER_LEN),
+
+ // Make sure it's to the right port. The following instruction
+ // adds the previously extracted IP header length to the given
+ // offset to locate the correct byte. The given offset of 6
+ // comprises the length of the pseudo header (4) plus the offset
+ // of the UDP destination port (2) within the UDP header.
+ BPF_STMT(BPF_LD + BPF_H + BPF_IND,
+ BPF_LOCAL_LOOPBACK_HEADER_LEN + UDP_DEST_PORT),
+ // The following instruction tests against the default DHCP server port,
+ // but the action port is actually set in PktFilterBPF::openSocket().
+ // N.B. The code in that method assumes that this instruction is at
+ // offset 8 in the program. If this is changed, openSocket() must be
+ // updated.
+ BPF_JUMP(BPF_JMP + BPF_JEQ + BPF_K, DHCP4_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),
+};
+
+
+}
+
+using namespace isc::util;
+
+namespace isc {
+namespace dhcp {
+
+SocketInfo
+PktFilterBPF::openSocket(Iface& iface,
+ const isc::asiolink::IOAddress& addr,
+ const uint16_t port, const bool,
+ const bool) {
+
+ // Open fallback socket first. If it fails, it will give us an indication
+ // that there is another service (perhaps DHCP server) running.
+ // The function will throw an exception and effectivelly cease opening
+ // the BPF device below.
+ int fallback = openFallbackSocket(addr, port);
+
+ // Fallback has opened, so let's open the BPF device that we will be
+ // using for receiving and sending packets. The BPF device is opened
+ // by opening a file /dev/bpf%d where %d is a number. There may be
+ // devices already open so we will try them one by one and open the
+ // one that is not busy.
+ int sock = -1;
+ for (unsigned int bpf_dev = 0;
+ bpf_dev < MAX_BPF_OPEN_ATTEMPTS && (sock < 0);
+ ++bpf_dev) {
+ std::ostringstream s;
+ s << "/dev/bpf" << bpf_dev;
+ sock = open(s.str().c_str(), O_RDWR, 0);
+ if (sock < 0) {
+ // If device is busy, try another one.
+ if (errno == EBUSY) {
+ continue;
+ }
+ // All other errors are fatal, so close the fallback socket
+ // and throw.
+ close(fallback);
+ isc_throw(SocketConfigError, "Failed to open BPF device " << s);
+ }
+ }
+
+ // The BPF device is now open. Now it needs to be configured.
+
+ // Associate the device with the interface name.
+ struct ifreq iface_data;
+ memset(&iface_data, 0, sizeof(iface_data));
+ std::strncpy(iface_data.ifr_name, iface.getName().c_str(),
+ std::min(static_cast<int>(IFNAMSIZ),
+ static_cast<int>(iface.getName().length())));
+ if (ioctl(sock, BIOCSETIF, &iface_data) < 0) {
+ close(fallback);
+ close(sock);
+ isc_throw(SocketConfigError, "Failed to associate BPF device "
+ " with interface " << iface.getName());
+ }
+
+ // Get the BPF version supported by the kernel. Every application
+ // must check this version against the current version in use.
+ struct bpf_version ver;
+ if (ioctl(sock, BIOCVERSION, &ver) < 0) {
+ close(fallback);
+ close(sock);
+ isc_throw(SocketConfigError, "Failed to obtain the BPF version"
+ " number from the kernel");
+ }
+ // Major BPF version must match and the minor version that the kernel
+ // runs must be at least the current version in use.
+ if ((ver.bv_major != BPF_MAJOR_VERSION) ||
+ (ver.bv_minor < BPF_MINOR_VERSION)) {
+ close(fallback);
+ close(sock);
+ isc_throw(SocketConfigError, "Invalid BPF version: "
+ << ver.bv_major << "." << ver.bv_minor
+ << " Expected at least version:"
+ << BPF_MAJOR_VERSION << "."
+ << BPF_MINOR_VERSION);;
+ }
+
+ // Get the size of the read buffer for this device. We will need to
+ // allocate the buffer of this size for packet reads.
+ unsigned int buf_len = 0;
+ if (ioctl(sock, BIOCGBLEN, &buf_len) < 0) {
+ close(fallback);
+ close(sock);
+ isc_throw(SocketConfigError, "Unable to obtain the required"
+ " buffer legth for reads from BPF device");
+ }
+
+ if (buf_len < sizeof(bpf_hdr)) {
+ isc_throw(SocketConfigError, "read buffer length returned by the"
+ " kernel for the BPF device associated with the interface"
+ << iface.getName() << " is lower than the BPF header"
+ " length: this condition is impossible unless the"
+ " operating system is really broken!");
+ }
+
+ // Set the filter program so as we only get packets we are interested in.
+ struct bpf_program prog;
+ memset(&prog, 0, sizeof(bpf_program));
+ if (iface.flag_loopback_) {
+ prog.bf_insns = loopback_ip_udp_filter;
+ prog.bf_len = sizeof(loopback_ip_udp_filter) / sizeof(struct bpf_insn);
+ // The address family is AF_INET. It can't be hardcoded in the BPF program
+ // because we need to make the host to network order conversion using htonl
+ // and conversion can't be done within the BPF program structure as it
+ // doesn't work on some systems.
+ prog.bf_insns[1].k = htonl(AF_INET);
+
+ } else {
+ prog.bf_insns = ethernet_ip_udp_filter;
+ prog.bf_len = sizeof(ethernet_ip_udp_filter) / sizeof(struct bpf_insn);
+ }
+
+ // Configure the BPF program to receive packets on the specified port.
+ prog.bf_insns[8].k = port;
+
+ // Actually set the filter program for the device.
+ if (ioctl(sock, BIOCSETF, &prog) < 0) {
+ close(fallback);
+ close(sock);
+ isc_throw(SocketConfigError, "Failed to install BPF filter"
+ " program");
+ }
+
+ // Configure the BPF device to use the immediate mode. This ensures
+ // that the read function returns immediatelly, instead of waiting
+ // for the kernel to fill up the buffer, which would likely cause
+ // read hangs.
+ int flag = 1;
+ if (ioctl(sock, BIOCIMMEDIATE, &flag) < 0) {
+ close(fallback);
+ close(sock);
+ isc_throw(SocketConfigError, "Failed to set promiscious mode for"
+ " BPF device");
+ }
+
+ // Everything is ok, allocate the read buffer and return the socket
+ // (BPF device descriptor) to the caller.
++ try {
++ iface.resizeReadBuffer(buf_len);
++
++ } catch (...) {
++ close(fallback);
++ close(sock);
++ throw;
++ }
+ return (SocketInfo(addr, port, sock, fallback));
+}
+
+Pkt4Ptr
+PktFilterBPF::receive(const Iface& iface, const SocketInfo& socket_info) {
+ // When using BPF, the read buffer must be allocated for the interface.
+ // If it is not allocated, it is a programmatic error.
+ if (iface.getReadBufferSize() == 0) {
+ isc_throw(SocketConfigError, "socket read buffer not allocated"
+ " for the interface: " << iface.getName());
+ }
+
+ // First let's get some data from the fallback socket. The data will be
+ // discarded but we don't want the socket buffer to bloat. We get the
+ // packets from the socket in loop but most of the time the loop will
+ // end after receiving one packet. The call to recv returns immediately
+ // when there is no data left on the socket because the socket is
+ // non-blocking.
+ // @todo In the normal conditions, both the primary socket and the fallback
+ // socket are in sync as they are set to receive packets on the same
+ // address and port. The reception of packets on the fallback socket
+ // shouldn't cause significant lags in packet reception. If we find in the
+ // future that it does, the sort of threshold could be set for the maximum
+ // bytes received on the fallback socket in a single round. Further
+ // optimizations would include an asynchronous read from the fallback socket
+ // when the DHCP server is idle.
+ int datalen;
+ do {
+ datalen = recv(socket_info.fallbackfd_, iface.getReadBuffer(),
+ iface.getReadBufferSize(), 0);
+ } while (datalen > 0);
+
+ datalen = read(socket_info.sockfd_, iface.getReadBuffer(),
+ iface.getReadBufferSize());
+ // If negative value is returned by read(), it indicates that an
+ // error occured. If returned value is 0, no data was read from the
+ // socket. In both cases something has gone wrong, because we expect
+ // that a chunk of data is there. We signal the lack of data by
+ // returing an empty packet.
+ if (datalen <= 0) {
+ return Pkt4Ptr();
+ }
+ datalen = BPF_WORDALIGN(datalen);
+
+ // Holds BPF header.
+ struct bpf_hdr bpfh;
+
+ /// @todo BPF may occasionally append more than one packet in a
+ /// single read. Our current libdhcp++ API is oriented towards receiving
+ /// one packet at the time so we just pick first usable packet here
+ /// and drop other packets. In the future the additional packets should
+ /// be queued and processed. For now, we just iterate over the packets
+ /// in the buffer and pick the first usable one.
+ int offset = 0;
+ while (offset < datalen) {
+ // Check if the BPF header fits in the reminder of the buffer.
+ // If it doesn't something is really wrong.
+ if (datalen - offset < sizeof(bpf_hdr)) {
+ isc_throw(SocketReadError, "packet received over the BPF device on"
+ " interface " << iface.getName() << " has a truncated "
+ " BPF header");
+ }
+
+ // Copy the BPF header.
+ memcpy(static_cast<void*>(&bpfh),
+ static_cast<void*>(iface.getReadBuffer()),
+ sizeof(bpfh));
+
+ // Check if the captured data fit into the reminder of the buffer.
+ // Again, something is really wrong here if it doesn't fit.
+ if (offset + bpfh.bh_hdrlen + bpfh.bh_caplen > datalen) {
+ isc_throw(SocketReadError, "packet received from the BPF device"
+ << " attached to interface " << iface.getName()
+ << " is truncated");
+ }
+
+ // Check if the whole packet has been captured.
+ if (bpfh.bh_caplen != bpfh.bh_datalen) {
+ // Not whole packet captured, proceed to next received packet.
+ offset = BPF_WORDALIGN(offset + bpfh.bh_hdrlen + bpfh.bh_caplen);
+ continue;
+ }
+
+ // All checks passed, let's use the packet at the offset found.
+ // Typically it will be at offset 0.
+ break;
+ };
+
+ // No parsable packet found, so return.
+ if (offset >= datalen) {
+ return (Pkt4Ptr());
+ }
+
+ // Skip the BPF header and create the buffer holding a frame.
+ InputBuffer buf(iface.getReadBuffer() + offset + bpfh.bh_hdrlen,
+ datalen - bpfh.bh_hdrlen - offset);
+
+
+ // @todo: This is awkward way to solve the chicken and egg problem
+ // whereby we don't know the offset where DHCP data start in the
+ // received buffer when we create the packet object. In general case,
+ // the IP header has variable length. The information about its length
+ // is stored in one of its fields. Therefore, we have to decode the
+ // packet to get the offset of the DHCP data. The dummy object is
+ // created so as we can pass it to the functions which decode IP stack
+ // and find actual offset of the DHCP data.
+ // Once we find the offset we can create another Pkt4 object from
+ // the reminder of the input buffer and set the IP addresses and
+ // ports from the dummy packet. We should consider doing it
+ // in some more elegant way.
+ Pkt4Ptr dummy_pkt = Pkt4Ptr(new Pkt4(DHCPDISCOVER, 0));
+
+ // On local loopback interface the ethernet header is not present.
+ // Instead, there is a 4-byte long pseudo header containing the
+ // address family in the host byte order.
+ if (iface.flag_loopback_) {
+ if (buf.getLength() < BPF_LOCAL_LOOPBACK_HEADER_LEN) {
+ isc_throw(SocketReadError, "packet received on local loopback"
+ " interface " << iface.getName() << " doesn't contain"
+ " the pseudo header with the address family type");
+ }
+ // Advance to the position of the IP header. We don't check the
+ // contents of the pseudo header because the BPF filter should have
+ // filtered out the packets with address family other than AF_INET.
+ buf.setPosition(BPF_LOCAL_LOOPBACK_HEADER_LEN);
+
+ // Since we don't decode the real link-layer header we need to
+ // supply the hardware address ourselves.
+ dummy_pkt->setLocalHWAddr(HWAddrPtr(new HWAddr()));
+ dummy_pkt->setRemoteHWAddr(HWAddrPtr(new HWAddr()));
+
+ } else {
+ // If we are on the interface other than local loopback, assume
+ // the ethernet header. For now we don't support any other data
+ // link layer.
+ decodeEthernetHeader(buf, dummy_pkt);
+ }
+
+ // Decode IP/UDP headers.
+ decodeIpUdpHeader(buf, dummy_pkt);
+
+ // Read the DHCP data.
+ std::vector<uint8_t> dhcp_buf;
+ buf.readVector(dhcp_buf, buf.getLength() - buf.getPosition());
+
+ // Decode DHCP data into the Pkt4 object.
+ Pkt4Ptr pkt = Pkt4Ptr(new Pkt4(&dhcp_buf[0], dhcp_buf.size()));
+
+ // Set the appropriate packet members using data collected from
+ // the decoded headers.
+ pkt->setIndex(iface.getIndex());
+ pkt->setIface(iface.getName());
+ pkt->setLocalAddr(dummy_pkt->getLocalAddr());
+ pkt->setRemoteAddr(dummy_pkt->getRemoteAddr());
+ pkt->setLocalPort(dummy_pkt->getLocalPort());
+ pkt->setRemotePort(dummy_pkt->getRemotePort());
+ pkt->setLocalHWAddr(dummy_pkt->getLocalHWAddr());
+ pkt->setRemoteHWAddr(dummy_pkt->getRemoteHWAddr());
+
+ return (pkt);
+}
+
+int
+PktFilterBPF::send(const Iface& iface, uint16_t sockfd, const Pkt4Ptr& pkt) {
+
+ OutputBuffer buf(14);
+
+ // Some interfaces may have no HW address - e.g. loopback interface.
+ // For these interfaces the HW address length is 0. If this is the case,
+ // then we will rely on the functions which construct the IP/UDP headers
+ // to provide a default HW address. Otherwise, create the HW address
+ // object using the HW address of the interface.
+ if (iface.getMacLen() > 0) {
+ HWAddrPtr hwaddr(new HWAddr(iface.getMac(), iface.getMacLen(),
+ iface.getHWType()));
+ pkt->setLocalHWAddr(hwaddr);
+ }
+
+ /// Loopback interface requires special treatment. It doesn't
+ /// use the ethernet header but rather a 4-bytes long pseudo header
+ /// holding an address family type (see bpf.c in OS sources).
+ if (iface.flag_loopback_) {
+ writeAFPseudoHeader(AF_INET, buf);
+
+ } else {
+ // Ethernet frame header.
+ // Note that we don't validate whether HW addresses in 'pkt'
+ // are valid because they are validated by the function called.
+ writeEthernetHeader(pkt, buf);
+ }
+
+ // IP and UDP header
+ writeIpUdpHeader(pkt, buf);
+
+ // DHCPv4 message
+ buf.writeData(pkt->getBuffer().getData(), pkt->getBuffer().getLength());
+
+ int result = write(sockfd, buf.getData(), buf.getLength());
+ if (result < 0) {
+ isc_throw(SocketWriteError, "failed to send DHCPv4 packet: "
+ << strerror(errno));
+ }
+
+ return (0);
+}
+
+void
+PktFilterBPF::writeAFPseudoHeader(const uint32_t address_family,
+ util::OutputBuffer& out_buf) {
+ // Copy address family to the temporary buffer and preserve the
+ // bytes order.
+ uint8_t af_buf[4];
+ memcpy(static_cast<void*>(af_buf),
+ static_cast<const void*>(&address_family),
+ sizeof(af_buf));
+ // Write the data into the buffer.
+ out_buf.writeData(af_buf, sizeof(af_buf));
+}
+
+} // end of isc::dhcp namespace
+} // end of isc namespace
projects / thirdparty / kea.git / commitdiff
