2ad7561f9f
When receiving lots of packets that are not meant for us, we waste a relatively large amount of cpu time computing their checksums before discarding them. Move the checksum calculation last so we never compute it for packets which would otherwise be discarded.
208 lines
6.4 KiB
C
208 lines
6.4 KiB
C
/***
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This file is part of systemd.
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Copyright (C) 2013 Intel Corporation. All rights reserved.
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Copyright (C) 2014 Tom Gundersen
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systemd is free software; you can redistribute it and/or modify it
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under the terms of the GNU Lesser General Public License as published by
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the Free Software Foundation; either version 2.1 of the License, or
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(at your option) any later version.
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systemd is distributed in the hope that it will be useful, but
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WITHOUT ANY WARRANTY; without even the implied warranty of
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MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the GNU
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Lesser General Public License for more details.
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You should have received a copy of the GNU Lesser General Public License
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along with systemd; If not, see <http://www.gnu.org/licenses/>.
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***/
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#include <stdlib.h>
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#include <errno.h>
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#include <string.h>
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#include <stdio.h>
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#include <net/ethernet.h>
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#include <net/if_arp.h>
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#include <sys/param.h>
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#include "util.h"
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#include "list.h"
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#include "dhcp-protocol.h"
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#include "dhcp-lease-internal.h"
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#include "dhcp-internal.h"
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#include "sd-dhcp-lease.h"
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#include "sd-dhcp-client.h"
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#define DHCP_CLIENT_MIN_OPTIONS_SIZE 312
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int dhcp_message_init(DHCPMessage *message, uint8_t op, uint32_t xid,
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uint8_t type, uint8_t **opt, size_t *optlen) {
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int err;
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assert(op == BOOTREQUEST || op == BOOTREPLY);
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*opt = (uint8_t *)(message + 1);
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if (*optlen < 4)
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return -ENOBUFS;
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*optlen -= 4;
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message->op = op;
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message->htype = ARPHRD_ETHER;
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message->hlen = ETHER_ADDR_LEN;
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message->xid = htobe32(xid);
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(*opt)[0] = 0x63;
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(*opt)[1] = 0x82;
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(*opt)[2] = 0x53;
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(*opt)[3] = 0x63;
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*opt += 4;
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err = dhcp_option_append(opt, optlen, DHCP_OPTION_MESSAGE_TYPE, 1,
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&type);
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if (err < 0)
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return err;
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return 0;
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}
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uint16_t dhcp_packet_checksum(void *buf, int len) {
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uint32_t sum;
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uint16_t *check;
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int i;
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uint8_t *odd;
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sum = 0;
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check = buf;
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for (i = 0; i < len / 2 ; i++)
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sum += check[i];
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if (len & 0x01) {
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odd = buf;
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sum += odd[len - 1];
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}
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while (sum >> 16)
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sum = (sum & 0xffff) + (sum >> 16);
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return ~sum;
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}
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void dhcp_packet_append_ip_headers(DHCPPacket *packet, be32_t source_addr,
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uint16_t source_port, be32_t destination_addr,
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uint16_t destination_port, uint16_t len) {
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packet->ip.version = IPVERSION;
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packet->ip.ihl = DHCP_IP_SIZE / 4;
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packet->ip.tot_len = htobe16(len);
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packet->ip.protocol = IPPROTO_UDP;
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packet->ip.saddr = source_addr;
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packet->ip.daddr = destination_addr;
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packet->udp.source = htobe16(source_port);
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packet->udp.dest = htobe16(destination_port);
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packet->udp.len = htobe16(len - DHCP_IP_SIZE);
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packet->ip.check = packet->udp.len;
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packet->udp.check = dhcp_packet_checksum(&packet->ip.ttl, len - 8);
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packet->ip.ttl = IPDEFTTL;
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packet->ip.check = 0;
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packet->ip.check = dhcp_packet_checksum(&packet->ip, DHCP_IP_SIZE);
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}
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int dhcp_packet_verify_headers(DHCPPacket *packet, size_t len, bool checksum) {
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size_t hdrlen;
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assert(packet);
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/* IP */
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if (len < DHCP_IP_SIZE) {
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log_dhcp_client(client, "ignoring packet: packet (%zu bytes) "
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" smaller than IP header (%u bytes)", len,
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DHCP_IP_SIZE);
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return -EINVAL;
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}
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if (packet->ip.version != IPVERSION) {
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log_dhcp_client(client, "ignoring packet: not IPv4");
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return -EINVAL;
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}
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if (packet->ip.ihl < 5) {
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log_dhcp_client(client, "ignoring packet: IPv4 IHL (%u words) invalid",
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packet->ip.ihl);
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return -EINVAL;
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}
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hdrlen = packet->ip.ihl * 4;
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if (hdrlen < 20) {
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log_dhcp_client(client, "ignoring packet: IPv4 IHL (%zu bytes) "
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"smaller than minimum (20 bytes)", hdrlen);
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return -EINVAL;
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}
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if (len < hdrlen) {
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log_dhcp_client(client, "ignoring packet: packet (%zu bytes) "
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"smaller than expected (%zu) by IP header", len,
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hdrlen);
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return -EINVAL;
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}
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/* UDP */
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if (packet->ip.protocol != IPPROTO_UDP) {
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log_dhcp_client(client, "ignoring packet: not UDP");
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return -EINVAL;
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}
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if (len < DHCP_IP_UDP_SIZE) {
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log_dhcp_client(client, "ignoring packet: packet (%zu bytes) "
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" smaller than IP+UDP header (%u bytes)", len,
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DHCP_IP_UDP_SIZE);
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return -EINVAL;
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}
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if (len < hdrlen + be16toh(packet->udp.len)) {
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log_dhcp_client(client, "ignoring packet: packet (%zu bytes) "
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"smaller than expected (%zu) by UDP header", len,
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hdrlen + be16toh(packet->udp.len));
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return -EINVAL;
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}
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if (be16toh(packet->udp.dest) != DHCP_PORT_CLIENT) {
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log_dhcp_client(client, "ignoring packet: to port %u, which "
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"is not the DHCP client port (%u)",
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be16toh(packet->udp.dest), DHCP_PORT_CLIENT);
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return -EINVAL;
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}
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/* checksums - computing these is relatively expensive, so only do it
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if all the other checks have passed
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*/
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if (dhcp_packet_checksum(&packet->ip, hdrlen)) {
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log_dhcp_client(client, "ignoring packet: invalid IP checksum");
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return -EINVAL;
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}
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if (checksum && packet->udp.check) {
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packet->ip.check = packet->udp.len;
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packet->ip.ttl = 0;
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if (dhcp_packet_checksum(&packet->ip.ttl,
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be16toh(packet->udp.len) + 12)) {
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log_dhcp_client(client, "ignoring packet: invalid UDP checksum");
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return -EINVAL;
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}
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}
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return 0;
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}
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