diff options
Diffstat (limited to 'src/libsystemd-network/sd-dhcp-server.c')
| -rw-r--r-- | src/libsystemd-network/sd-dhcp-server.c | 150 |
1 files changed, 150 insertions, 0 deletions
diff --git a/src/libsystemd-network/sd-dhcp-server.c b/src/libsystemd-network/sd-dhcp-server.c index 37f81588c3..994c7beb31 100644 --- a/src/libsystemd-network/sd-dhcp-server.c +++ b/src/libsystemd-network/sd-dhcp-server.c @@ -127,6 +127,156 @@ int sd_dhcp_server_stop(sd_dhcp_server *server) { return 0; } +static int dhcp_server_send_unicast_raw(sd_dhcp_server *server, DHCPPacket *packet, + size_t len) { + union sockaddr_union link = { + .ll.sll_family = AF_PACKET, + .ll.sll_protocol = htons(ETH_P_IP), + .ll.sll_ifindex = server->index, + .ll.sll_halen = ETH_ALEN, + }; + int r; + + assert(server); + assert(server->index > 0); + assert(server->address); + assert(packet); + assert(len > sizeof(DHCPPacket)); + + memcpy(&link.ll.sll_addr, &packet->dhcp.chaddr, ETH_ALEN); + + dhcp_packet_append_ip_headers(packet, server->address, DHCP_PORT_SERVER, + packet->dhcp.yiaddr, DHCP_PORT_CLIENT, len); + + r = dhcp_network_send_raw_socket(server->fd_raw, &link, packet, len); + if (r < 0) + return r; + + return 0; +} + +static int dhcp_server_send_udp(sd_dhcp_server *server, be32_t destination, + DHCPMessage *message, size_t len) { + union sockaddr_union dest = { + .in.sin_family = AF_INET, + .in.sin_port = htobe16(DHCP_PORT_CLIENT), + .in.sin_addr.s_addr = destination, + }; + struct iovec iov = { + .iov_base = message, + .iov_len = len, + }; + uint8_t cmsgbuf[CMSG_LEN(sizeof(struct in_pktinfo))] = {}; + struct msghdr msg = { + .msg_name = &dest, + .msg_namelen = sizeof(dest.in), + .msg_iov = &iov, + .msg_iovlen = 1, + .msg_control = cmsgbuf, + .msg_controllen = sizeof(cmsgbuf), + }; + struct cmsghdr *cmsg; + struct in_pktinfo *pktinfo; + int r; + + assert(server); + assert(server->fd > 0); + assert(message); + assert(len > sizeof(DHCPMessage)); + + cmsg = CMSG_FIRSTHDR(&msg); + assert(cmsg); + + cmsg->cmsg_level = IPPROTO_IP; + cmsg->cmsg_type = IP_PKTINFO; + cmsg->cmsg_len = CMSG_LEN(sizeof(struct in_pktinfo)); + + /* we attach source interface and address info to the message + rather than binding the socket. This will be mostly useful + when we gain support for arbitrary number of server addresses + */ + pktinfo = (struct in_pktinfo*) CMSG_DATA(cmsg); + assert(pktinfo); + + pktinfo->ipi_ifindex = server->index; + pktinfo->ipi_spec_dst.s_addr = server->address; + + r = sendmsg(server->fd, &msg, 0); + if (r < 0) + return -errno; + + return 0; +} + +static bool requested_broadcast(DHCPRequest *req) { + assert(req); + + return req->message->flags & htobe16(0x8000); +} + +int dhcp_server_send_packet(sd_dhcp_server *server, + DHCPRequest *req, DHCPPacket *packet, + int type, size_t optoffset) { + be32_t destination = INADDR_ANY; + int r; + + assert(server); + assert(req); + assert(req->max_optlen); + assert(optoffset <= req->max_optlen); + assert(packet); + + r = dhcp_option_append(&packet->dhcp, req->max_optlen, &optoffset, 0, + DHCP_OPTION_SERVER_IDENTIFIER, + 4, &server->address); + if (r < 0) + return r; + + r = dhcp_option_append(&packet->dhcp, req->max_optlen, &optoffset, 0, + DHCP_OPTION_END, 0, NULL); + if (r < 0) + return r; + + /* RFC 2131 Section 4.1 + + If the ’giaddr’ field in a DHCP message from a client is non-zero, + the server sends any return messages to the ’DHCP server’ port on the + BOOTP relay agent whose address appears in ’giaddr’. If the ’giaddr’ + field is zero and the ’ciaddr’ field is nonzero, then the server + unicasts DHCPOFFER and DHCPACK messages to the address in ’ciaddr’. + If ’giaddr’ is zero and ’ciaddr’ is zero, and the broadcast bit is + set, then the server broadcasts DHCPOFFER and DHCPACK messages to + 0xffffffff. If the broadcast bit is not set and ’giaddr’ is zero and + ’ciaddr’ is zero, then the server unicasts DHCPOFFER and DHCPACK + messages to the client’s hardware address and ’yiaddr’ address. In + all cases, when ’giaddr’ is zero, the server broadcasts any DHCPNAK + messages to 0xffffffff. + + Section 4.3.2 + + If ’giaddr’ is set in the DHCPREQUEST message, the client is on a + different subnet. The server MUST set the broadcast bit in the + DHCPNAK, so that the relay agent will broadcast the DHCPNAK to the + client, because the client may not have a correct network address + or subnet mask, and the client may not be answering ARP requests. + */ + if (req->message->giaddr) { + destination = req->message->giaddr; + if (type == DHCP_NAK) + packet->dhcp.flags = htobe16(0x8000); + } else if (req->message->ciaddr && type != DHCP_NAK) + destination = req->message->ciaddr; + + if (destination || requested_broadcast(req) || type == DHCP_NAK) + return dhcp_server_send_udp(server, destination, &packet->dhcp, + sizeof(DHCPMessage) + optoffset); + else + /* we cannot send UDP packet to specific MAC address when the address is + not yet configured, so must fall back to raw packets */ + return dhcp_server_send_unicast_raw(server, packet, + sizeof(DHCPPacket) + optoffset); +} + static int parse_request(uint8_t code, uint8_t len, const uint8_t *option, void *user_data) { DHCPRequest *req = user_data; |