raw.c

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/*
 *   This library is free software; you can redistribute it and/or
 *   modify it under the terms of the GNU Lesser General Public
 *   License as published by the Free Software Foundation; either
 *   version 2.1 of the License, or (at your option) any later version.
 *
 *   This library is distributed in the hope that it will be useful,
 *   but WITHOUT ANY WARRANTY; without even the implied warranty of
 *   MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the GNU
 *   Lesser General Public License for more details.
 *
 *   You should have received a copy of the GNU Lesser General Public
 *   License along with this library; if not, write to the Free Software
 *   Foundation, Inc., 51 Franklin St, Fifth Floor, Boston, MA 02110-1301, USA
 */
 
/**
 * $Id: b06c0d30bd24f71474616adfa5caed0d5795f6c9 $
 *
 * @file protocols/dhcpv4/raw.c
 * @brief Send/recv DHCP packets using raw sockets.
 *
 * @copyright 2008,2017 The FreeRADIUS server project
 * @copyright 2008 Alan DeKok (aland@deployingradius.com)
 */
#include "attrs.h"
#include "dhcpv4.h"
 
#include <freeradius-devel/util/net.h>
#include <freeradius-devel/util/pair.h>
#include <freeradius-devel/util/proto.h>
#include <freeradius-devel/util/syserror.h>
#include <freeradius-devel/util/udpfromto.h>
 
#include <sys/ioctl.h>
 
#ifdef HAVE_SYS_SOCKET_H
#endif
#ifdef HAVE_SYS_TYPES_H
#endif
 
#ifdef HAVE_LINUX_IF_PACKET_H
#  include <linux/if_ether.h>
#endif
 
#include <net/if_arp.h>
 
#ifdef HAVE_LINUX_IF_PACKET_H
/** Open a raw socket to read/write packets from/to
 *
 * @param[out] link_layer       A sockaddr_ll struct to populate.  Must be passed to other raw
 *                              functions.
 * @param[in] ifindex           of the interface we're binding to.
 * @return
 *      - >= 0 a file descriptor to read/write packets on.
 *      - <0 an error occurred.
 */
int fr_dhcpv4_raw_socket_open(struct sockaddr_ll *link_layer, int ifindex)
{
        int fd;
 
        /*
         * PF_PACKET - packet interface on device level.
         * using a raw socket allows packet data to be unchanged by the device driver.
         */
        fd = socket(PF_PACKET, SOCK_RAW, htons(ETH_P_ALL));
        if (fd < 0) {
                fr_strerror_printf("Cannot open socket: %s", fr_syserror(errno));
                return fd;
        }
 
        /* Set link layer parameters */
        memset(link_layer, 0, sizeof(struct sockaddr_ll));
 
        link_layer->sll_family = AF_PACKET;
        link_layer->sll_protocol = htons(ETH_P_ALL);
        link_layer->sll_ifindex = ifindex;
        link_layer->sll_hatype = ARPHRD_ETHER;
        link_layer->sll_pkttype = PACKET_OTHERHOST;
        link_layer->sll_halen = 6;
 
        if (bind(fd, (struct sockaddr *)link_layer, sizeof(struct sockaddr_ll)) < 0) {
                close(fd);
                fr_strerror_printf("Cannot bind raw socket: %s", fr_syserror(errno));
                return -1;
        }
 
        return fd;
}
 
/** Create the requisite L2/L3 headers, and write a DHCPv4 packet to a raw socket
 *
 * @param[in] sockfd            to write to.
 * @param[in] link_layer        information, as returned by fr_dhcpv4_raw_socket_open.
 * @param[in] packet            to write.
 * @param[in] list              to send.
 * @return
 *      - 0 on success.
 *      - -1 on failure.
 */
int fr_dhcpv4_raw_packet_send(int sockfd, struct sockaddr_ll *link_layer,
                              fr_packet_t *packet, fr_pair_list_t *list)
{
        uint8_t                 dhcp_packet[1518] = { 0 };
        ethernet_header_t       *eth_hdr = (ethernet_header_t *)dhcp_packet;
        ip_header_t             *ip_hdr = (ip_header_t *)(dhcp_packet + ETH_HDR_SIZE);
        udp_header_t            *udp_hdr = (udp_header_t *) (dhcp_packet + ETH_HDR_SIZE + IP_HDR_SIZE);
        dhcp_packet_t           *dhcp = (dhcp_packet_t *)(dhcp_packet + ETH_HDR_SIZE + IP_HDR_SIZE + UDP_HDR_SIZE);
 
        uint16_t                l4_len = (UDP_HDR_SIZE + packet->data_len);
        fr_pair_t               *vp;
 
        /* set ethernet source address to our MAC address (Client-Hardware-Address). */
        uint8_t dhmac[ETH_ADDR_LEN] = { 0 };
        if ((vp = fr_pair_find_by_da(list, NULL, attr_dhcp_client_hardware_address))) {
                if (vp->vp_type == FR_TYPE_ETHERNET) memcpy(dhmac, vp->vp_ether, sizeof(vp->vp_ether));
        }
 
        /* fill in Ethernet layer (L2) */
        memcpy(eth_hdr->dst_addr, eth_bcast, ETH_ADDR_LEN);
        memcpy(eth_hdr->src_addr, dhmac, ETH_ADDR_LEN);
        eth_hdr->ether_type = htons(ETH_TYPE_IP);
 
        /* fill in IP layer (L3) */
        ip_hdr->ip_vhl = IP_VHL(4, 5);
        ip_hdr->ip_tos = 0;
        ip_hdr->ip_len = htons(IP_HDR_SIZE +  UDP_HDR_SIZE + packet->data_len);
        ip_hdr->ip_id = 0;
        ip_hdr->ip_off = 0;
        ip_hdr->ip_ttl = 64;
        ip_hdr->ip_p = 17;
        ip_hdr->ip_sum = 0; /* Filled later */
 
        /* saddr: packet src IP addr (default: 0.0.0.0). */
        ip_hdr->ip_src.s_addr = packet->socket.inet.src_ipaddr.addr.v4.s_addr;
 
        /* daddr: packet destination IP addr (should be 255.255.255.255 for broadcast). */
        ip_hdr->ip_dst.s_addr = packet->socket.inet.dst_ipaddr.addr.v4.s_addr;
 
        /* IP header checksum */
        ip_hdr->ip_sum = fr_ip_header_checksum((uint8_t const *)ip_hdr, 5);
 
        udp_hdr->src = htons(packet->socket.inet.src_port);
        udp_hdr->dst = htons(packet->socket.inet.dst_port);
 
        udp_hdr->len = htons(l4_len);
        udp_hdr->checksum = 0; /* UDP checksum will be done after dhcp header */
 
        /* DHCP layer (L7) */
 
        /* just copy what FreeRADIUS has encoded for us. */
        memcpy(dhcp, packet->data, packet->data_len);
 
        /* UDP checksum is done here */
        udp_hdr->checksum = fr_udp_checksum((uint8_t const *)(dhcp_packet + ETH_HDR_SIZE + IP_HDR_SIZE),
                                            l4_len, udp_hdr->checksum,
                                            packet->socket.inet.src_ipaddr.addr.v4, packet->socket.inet.dst_ipaddr.addr.v4);
 
        return sendto(sockfd, dhcp_packet, (ETH_HDR_SIZE + IP_HDR_SIZE + UDP_HDR_SIZE + packet->data_len),
                      0, (struct sockaddr *) link_layer, sizeof(struct sockaddr_ll));
}
 
/*
 *      For a client, receive a DHCP packet from a raw packet
 *      socket. Make sure it matches the ongoing request.
 *
 *      FIXME: split this into two, recv_raw_packet, and verify(packet, original)
 */
fr_packet_t *fr_dhcpv4_raw_packet_recv(int sockfd, struct sockaddr_ll *link_layer,
                                             fr_packet_t *request, fr_pair_list_t *list)
{
        fr_pair_t               *vp;
        fr_packet_t             *packet;
        dhcp_packet_t           *dhcp_data;
        uint8_t const           *code;
        uint32_t                magic, xid;
        ssize_t                 data_len;
 
        uint8_t                 *raw_packet;
        ethernet_header_t       *eth_hdr;
        ip_header_t             *ip_hdr;
        udp_header_t            *udp_hdr;
        dhcp_packet_t           *dhcp_hdr;
        uint16_t                udp_src_port;
        uint16_t                udp_dst_port;
        size_t                  dhcp_data_len;
        socklen_t               sock_len;
        uint8_t                 data_offset;
 
        packet = fr_packet_alloc(NULL, false);
        if (!packet) {
                fr_strerror_const("Failed allocating packet");
                return NULL;
        }
 
        raw_packet = talloc_zero_array(packet, uint8_t, MAX_PACKET_SIZE);
        if (!raw_packet) {
                fr_strerror_const("Out of memory");
                fr_packet_free(&packet);
                return NULL;
        }
 
        packet->socket.fd = sockfd;
 
        /* a packet was received (but maybe it is not for us) */
        sock_len = sizeof(struct sockaddr_ll);
        data_len = recvfrom(sockfd, raw_packet, MAX_PACKET_SIZE, 0, (struct sockaddr *)link_layer, &sock_len);
 
        data_offset = ETH_HDR_SIZE + IP_HDR_SIZE + UDP_HDR_SIZE; /* DHCP data after Ethernet, IP, UDP */
 
        if (data_len <= data_offset) DISCARD_RP("Payload (%d) smaller than required for layers 2+3+4", (int)data_len);
 
        /* map raw packet to packet header of the different layers (Ethernet, IP, UDP) */
        eth_hdr = (ethernet_header_t *)raw_packet;
 
        /*
         *      Check Ethernet layer data (L2)
         */
        if (ntohs(eth_hdr->ether_type) != ETH_TYPE_IP) DISCARD_RP("Ethernet type (%d) != IP",
            ntohs(eth_hdr->ether_type));
 
        /*
         *      If Ethernet destination is not broadcast (ff:ff:ff:ff:ff:ff)
         *      Check if it matches the source HW address used (Client-Hardware-Address = 267)
         */
        if ((memcmp(&eth_bcast, &eth_hdr->dst_addr, ETH_ADDR_LEN) != 0) &&
            (vp = fr_pair_find_by_da(list, NULL, attr_dhcp_client_hardware_address)) &&
            ((vp->vp_type == FR_TYPE_ETHERNET) && (memcmp(vp->vp_ether, &eth_hdr->dst_addr, ETH_ADDR_LEN) != 0))) {
 
                /* No match. */
                DISCARD_RP("Ethernet destination (%pV) is not broadcast and doesn't match request source (%pV)",
                           fr_box_ether(eth_hdr->dst_addr), &vp->data);
        }
 
        /*
         *      Ethernet is OK.  Now look at IP.
         */
        ip_hdr = (ip_header_t *)(raw_packet + ETH_HDR_SIZE);
 
        /*
         *      Check IPv4 layer data (L3)
         */
        if (ip_hdr->ip_p != IPPROTO_UDP) DISCARD_RP("IP protocol (%d) != UDP", ip_hdr->ip_p);
 
        /*
         *      note: checking the destination IP address is not
         *      useful (it would be the offered IP address - which we
         *      don't know beforehand, or the broadcast address).
         */
 
        /*
         *      Now check UDP.
         */
        udp_hdr = (udp_header_t *)(raw_packet + ETH_HDR_SIZE + IP_HDR_SIZE);
 
        /*
         *      Check UDP layer data (L4)
         */
        udp_src_port = ntohs(udp_hdr->src);
        udp_dst_port = ntohs(udp_hdr->dst);
 
        /*
         *      Check DHCP layer data
         */
        dhcp_data_len = data_len - data_offset;
 
        if (dhcp_data_len < MIN_PACKET_SIZE) DISCARD_RP("DHCP packet is too small (%zu < %i)",
                                                        dhcp_data_len, MIN_PACKET_SIZE);
        if (dhcp_data_len > MAX_PACKET_SIZE) DISCARD_RP("DHCP packet is too large (%zu > %i)",
                                                        dhcp_data_len, MAX_PACKET_SIZE);
 
        dhcp_hdr = (dhcp_packet_t *)(raw_packet + ETH_HDR_SIZE + IP_HDR_SIZE + UDP_HDR_SIZE);
 
        if (dhcp_hdr->htype != 1) DISCARD_RP("DHCP hardware type (%d) != Ethernet (1)", dhcp_hdr->htype);
        if (dhcp_hdr->hlen != 6) DISCARD_RP("DHCP hardware address length (%d) != 6", dhcp_hdr->hlen);
 
        magic = ntohl(dhcp_hdr->option_format);
 
        if (magic != DHCP_OPTION_MAGIC_NUMBER) DISCARD_RP("DHCP magic cookie (0x%04x) != DHCP (0x%04x)",
                                                          magic, DHCP_OPTION_MAGIC_NUMBER);
 
        /*
         *      Reply transaction id must match value from request.
         */
        xid = ntohl(dhcp_hdr->xid);
        if (xid != (uint32_t)request->id) DISCARD_RP("DHCP transaction ID (0x%04x) != xid from request (0x%04x)",
                                                     xid, request->id)
 
        /*
         *      all checks ok! this is a DHCP reply we're interested in.
         *
         *      dhcp_data is present to avoid what appears to coverity
         *      to be a cast from a less aligned type to a more aligned
         *      type in the fr_dhcpv4_packet_get_option() call, even though
         *      talloc_memdup() returns a pointer aligned to TALLOC_ALIGN
         *      bytes.
         */
        packet->data_len = dhcp_data_len;
        dhcp_data = talloc_memdup(packet, raw_packet + data_offset, dhcp_data_len);
        packet->data = (uint8_t *) dhcp_data;
        TALLOC_FREE(raw_packet);
        packet->id = xid;
 
        code = fr_dhcpv4_packet_get_option((dhcp_packet_t const *)dhcp_data,
                                           packet->data_len, attr_dhcp_message_type);
        if (!code) {
                fr_strerror_const("No message-type option was found in the packet");
                fr_packet_free(&packet);
                return NULL;
        }
 
        if ((code[1] < 1) || (code[2] == 0) || (code[2] > 8)) {
                fr_strerror_const("Unknown value for message-type option");
                fr_packet_free(&packet);
                return NULL;
        }
 
        packet->code = code[2];
 
        packet->socket.inet.src_port = udp_src_port;
        packet->socket.inet.dst_port = udp_dst_port;
 
        packet->socket.inet.src_ipaddr.af = AF_INET;
        packet->socket.inet.src_ipaddr.addr.v4.s_addr = ip_hdr->ip_src.s_addr;
        packet->socket.inet.dst_ipaddr.af = AF_INET;
        packet->socket.inet.dst_ipaddr.addr.v4.s_addr = ip_hdr->ip_dst.s_addr;
 
        return packet;
}
#endif