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143 lines
4.8 KiB
143 lines
4.8 KiB
/*
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This file is part of NetGuard.
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NetGuard is free software: you can redistribute it and/or modify
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it under the terms of the GNU General Public License as published by
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the Free Software Foundation, either version 3 of the License, or
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(at your option) any later version.
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NetGuard is distributed in the hope that it will be useful,
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but WITHOUT ANY WARRANTY; without even the implied warranty of
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MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the
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GNU General Public License for more details.
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You should have received a copy of the GNU General Public License
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along with NetGuard. If not, see <http://www.gnu.org/licenses/>.
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Copyright 2015-2019 by Marcel Bokhorst (M66B)
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*/
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#include "netguard.h"
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int check_dhcp(const struct arguments *args, const struct udp_session *u,
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const uint8_t *data, const size_t datalen) {
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// This is untested
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// Android routing of DHCP is erroneous
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log_android(ANDROID_LOG_WARN, "DHCP check");
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if (datalen < sizeof(struct dhcp_packet)) {
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log_android(ANDROID_LOG_WARN, "DHCP packet size %d", datalen);
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return -1;
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}
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const struct dhcp_packet *request = (struct dhcp_packet *) data;
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if (ntohl(request->option_format) != DHCP_OPTION_MAGIC_NUMBER) {
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log_android(ANDROID_LOG_WARN, "DHCP invalid magic %x", request->option_format);
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return -1;
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}
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if (request->htype != 1 || request->hlen != 6) {
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log_android(ANDROID_LOG_WARN, "DHCP unknown hardware htype %d hlen %d",
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request->htype, request->hlen);
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return -1;
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}
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log_android(ANDROID_LOG_WARN, "DHCP opcode", request->opcode);
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// Discover: source 0.0.0.0:68 destination 255.255.255.255:67
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// Offer: source 10.1.10.1:67 destination 255.255.255.255:68
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// Request: source 0.0.0.0:68 destination 255.255.255.255:67
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// Ack: source: 10.1.10.1 destination: 255.255.255.255
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if (request->opcode == 1) { // Discover/request
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struct dhcp_packet *response = ng_calloc(500, 1, "dhcp");
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// Hack
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inet_pton(AF_INET, "10.1.10.1", (void *) &u->saddr);
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/*
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Discover:
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DHCP option 53: DHCP Discover
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DHCP option 50: 192.168.1.100 requested
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DHCP option 55: Parameter Request List:
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Request Subnet Mask (1), Router (3), Domain Name (15), Domain Name Server (6)
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Request
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DHCP option 53: DHCP Request
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DHCP option 50: 192.168.1.100 requested
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DHCP option 54: 192.168.1.1 DHCP server.
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*/
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memcpy(response, request, sizeof(struct dhcp_packet));
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response->opcode = (uint8_t) (request->siaddr == 0 ? 2 /* Offer */ : /* Ack */ 4);
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response->secs = 0;
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response->flags = 0;
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memset(&response->ciaddr, 0, sizeof(response->ciaddr));
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inet_pton(AF_INET, "10.1.10.2", &response->yiaddr);
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inet_pton(AF_INET, "10.1.10.1", &response->siaddr);
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memset(&response->giaddr, 0, sizeof(response->giaddr));
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// https://tools.ietf.org/html/rfc2132
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uint8_t *options = (uint8_t *) (response + sizeof(struct dhcp_packet));
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int idx = 0;
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*(options + idx++) = 53; // Message type
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*(options + idx++) = 1;
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*(options + idx++) = (uint8_t) (request->siaddr == 0 ? 2 : 5);
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/*
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1 DHCPDISCOVER
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2 DHCPOFFER
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3 DHCPREQUEST
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4 DHCPDECLINE
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5 DHCPACK
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6 DHCPNAK
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7 DHCPRELEASE
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8 DHCPINFORM
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*/
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*(options + idx++) = 1; // subnet mask
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*(options + idx++) = 4; // IP4 length
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inet_pton(AF_INET, "255.255.255.0", options + idx);
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idx += 4;
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*(options + idx++) = 3; // gateway
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*(options + idx++) = 4; // IP4 length
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inet_pton(AF_INET, "10.1.10.1", options + idx);
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idx += 4;
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*(options + idx++) = 51; // lease time
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*(options + idx++) = 4; // quad
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*((uint32_t *) (options + idx)) = 3600;
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idx += 4;
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*(options + idx++) = 54; // DHCP
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*(options + idx++) = 4; // IP4 length
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inet_pton(AF_INET, "10.1.10.1", options + idx);
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idx += 4;
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*(options + idx++) = 6; // DNS
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*(options + idx++) = 4; // IP4 length
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inet_pton(AF_INET, "8.8.8.8", options + idx);
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idx += 4;
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*(options + idx++) = 255; // End
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/*
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DHCP option 53: DHCP Offer
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DHCP option 1: 255.255.255.0 subnet mask
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DHCP option 3: 192.168.1.1 router
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DHCP option 51: 86400s (1 day) IP address lease time
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DHCP option 54: 192.168.1.1 DHCP server
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DHCP option 6: DNS servers 9.7.10.15
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*/
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write_udp(args, u, (uint8_t *) response, 500);
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ng_free(response, __FILE__, __LINE__);
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}
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return 0;
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}
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