diff options
Diffstat (limited to 'src/libsystemd-network/dhcp-packet.c')
| -rw-r--r-- | src/libsystemd-network/dhcp-packet.c | 168 |
1 files changed, 168 insertions, 0 deletions
diff --git a/src/libsystemd-network/dhcp-packet.c b/src/libsystemd-network/dhcp-packet.c new file mode 100644 index 0000000..ad5f8e2 --- /dev/null +++ b/src/libsystemd-network/dhcp-packet.c @@ -0,0 +1,168 @@ +/* SPDX-License-Identifier: LGPL-2.1+ */ +/*** + Copyright © 2013 Intel Corporation. All rights reserved. +***/ + +#include <errno.h> +#include <net/ethernet.h> +#include <net/if_arp.h> +#include <string.h> + +#include "dhcp-internal.h" +#include "dhcp-protocol.h" + +#define DHCP_CLIENT_MIN_OPTIONS_SIZE 312 + +int dhcp_message_init(DHCPMessage *message, uint8_t op, uint32_t xid, + uint8_t type, uint16_t arp_type, size_t optlen, + size_t *optoffset) { + size_t offset = 0; + int r; + + assert(IN_SET(op, BOOTREQUEST, BOOTREPLY)); + assert(IN_SET(arp_type, ARPHRD_ETHER, ARPHRD_INFINIBAND)); + + message->op = op; + message->htype = arp_type; + message->hlen = (arp_type == ARPHRD_ETHER) ? ETHER_ADDR_LEN : 0; + message->xid = htobe32(xid); + message->magic = htobe32(DHCP_MAGIC_COOKIE); + + r = dhcp_option_append(message, optlen, &offset, 0, + SD_DHCP_OPTION_MESSAGE_TYPE, 1, &type); + if (r < 0) + return r; + + *optoffset = offset; + + return 0; +} + +uint16_t dhcp_packet_checksum(uint8_t *buf, size_t len) { + uint64_t *buf_64 = (uint64_t*)buf; + uint64_t *end_64 = buf_64 + (len / sizeof(uint64_t)); + uint64_t sum = 0; + + /* See RFC1071 */ + + while (buf_64 < end_64) { + sum += *buf_64; + if (sum < *buf_64) + /* wrap around in one's complement */ + sum++; + + buf_64++; + } + + if (len % sizeof(uint64_t)) { + /* If the buffer is not aligned to 64-bit, we need + to zero-pad the last few bytes and add them in */ + uint64_t buf_tail = 0; + + memcpy(&buf_tail, buf_64, len % sizeof(uint64_t)); + + sum += buf_tail; + if (sum < buf_tail) + /* wrap around */ + sum++; + } + + while (sum >> 16) + sum = (sum & 0xffff) + (sum >> 16); + + return ~sum; +} + +void dhcp_packet_append_ip_headers(DHCPPacket *packet, be32_t source_addr, + uint16_t source_port, be32_t destination_addr, + uint16_t destination_port, uint16_t len) { + packet->ip.version = IPVERSION; + packet->ip.ihl = DHCP_IP_SIZE / 4; + packet->ip.tot_len = htobe16(len); + + packet->ip.tos = IPTOS_CLASS_CS6; + + packet->ip.protocol = IPPROTO_UDP; + packet->ip.saddr = source_addr; + packet->ip.daddr = destination_addr; + + packet->udp.source = htobe16(source_port); + packet->udp.dest = htobe16(destination_port); + + packet->udp.len = htobe16(len - DHCP_IP_SIZE); + + packet->ip.check = packet->udp.len; + packet->udp.check = dhcp_packet_checksum((uint8_t*)&packet->ip.ttl, len - 8); + + packet->ip.ttl = IPDEFTTL; + packet->ip.check = 0; + packet->ip.check = dhcp_packet_checksum((uint8_t*)&packet->ip, DHCP_IP_SIZE); +} + +int dhcp_packet_verify_headers(DHCPPacket *packet, size_t len, bool checksum, uint16_t port) { + size_t hdrlen; + + assert(packet); + + /* IP */ + + if (packet->ip.version != IPVERSION) + return log_debug_errno(SYNTHETIC_ERRNO(EINVAL), + "ignoring packet: not IPv4"); + + if (packet->ip.ihl < 5) + return log_debug_errno(SYNTHETIC_ERRNO(EINVAL), + "ignoring packet: IPv4 IHL (%u words) invalid", + packet->ip.ihl); + + hdrlen = packet->ip.ihl * 4; + if (hdrlen < 20) + return log_debug_errno(SYNTHETIC_ERRNO(EINVAL), + "ignoring packet: IPv4 IHL (%zu bytes) " + "smaller than minimum (20 bytes)", + hdrlen); + + if (len < hdrlen) + return log_debug_errno(SYNTHETIC_ERRNO(EINVAL), + "ignoring packet: packet (%zu bytes) " + "smaller than expected (%zu) by IP header", + len, hdrlen); + + /* UDP */ + + if (packet->ip.protocol != IPPROTO_UDP) + return log_debug_errno(SYNTHETIC_ERRNO(EINVAL), + "ignoring packet: not UDP"); + + if (len < hdrlen + be16toh(packet->udp.len)) + return log_debug_errno(SYNTHETIC_ERRNO(EINVAL), + "ignoring packet: packet (%zu bytes) " + "smaller than expected (%zu) by UDP header", + len, hdrlen + be16toh(packet->udp.len)); + + if (be16toh(packet->udp.dest) != port) + return log_debug_errno(SYNTHETIC_ERRNO(EINVAL), + "ignoring packet: to port %u, which " + "is not the DHCP client port (%u)", + be16toh(packet->udp.dest), port); + + /* checksums - computing these is relatively expensive, so only do it + if all the other checks have passed + */ + + if (dhcp_packet_checksum((uint8_t*)&packet->ip, hdrlen)) + return log_debug_errno(SYNTHETIC_ERRNO(EINVAL), + "ignoring packet: invalid IP checksum"); + + if (checksum && packet->udp.check) { + packet->ip.check = packet->udp.len; + packet->ip.ttl = 0; + + if (dhcp_packet_checksum((uint8_t*)&packet->ip.ttl, + be16toh(packet->udp.len) + 12)) + return log_debug_errno(SYNTHETIC_ERRNO(EINVAL), + "ignoring packet: invalid UDP checksum"); + } + + return 0; +} |