src/resolve/resolved-dns-packet.h

   1 /* SPDX-License-Identifier: LGPL-2.1+ */
   2 #pragma once
   3
   4 /***
   5   This file is part of systemd.
   6
   7   Copyright 2014 Lennart Poettering
   8
   9   systemd is free software; you can redistribute it and/or modify it
  10   under the terms of the GNU Lesser General Public License as published by
  11   the Free Software Foundation; either version 2.1 of the License, or
  12   (at your option) any later version.
  13
  14   systemd is distributed in the hope that it will be useful, but
  15   WITHOUT ANY WARRANTY; without even the implied warranty of
  16   MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the GNU
  17   Lesser General Public License for more details.
  18
  19   You should have received a copy of the GNU Lesser General Public License
  20   along with systemd; If not, see <http://www.gnu.org/licenses/>.
  21  ***/
  22
  23 #include <netinet/ip.h>
  24 #include <netinet/udp.h>
  25
  26 #include "hashmap.h"
  27 #include "in-addr-util.h"
  28 #include "macro.h"
  29 #include "sparse-endian.h"
  30
  31 typedef struct DnsPacketHeader DnsPacketHeader;
  32 typedef struct DnsPacket DnsPacket;
  33
  34 #include "resolved-def.h"
  35 #include "resolved-dns-answer.h"
  36 #include "resolved-dns-question.h"
  37 #include "resolved-dns-rr.h"
  38
  39 typedef enum DnsProtocol {
  40         DNS_PROTOCOL_DNS,
  41         DNS_PROTOCOL_MDNS,
  42         DNS_PROTOCOL_LLMNR,
  43         _DNS_PROTOCOL_MAX,
  44         _DNS_PROTOCOL_INVALID = -1
  45 } DnsProtocol;
  46
  47 struct DnsPacketHeader {
  48         uint16_t id;
  49         be16_t flags;
  50         be16_t qdcount;
  51         be16_t ancount;
  52         be16_t nscount;
  53         be16_t arcount;
  54 };
  55
  56 #define DNS_PACKET_HEADER_SIZE sizeof(DnsPacketHeader)
  57 #define UDP_PACKET_HEADER_SIZE (sizeof(struct iphdr) + sizeof(struct udphdr))
  58
  59 /* The various DNS protocols deviate in how large a packet can grow,
  60  * but the TCP transport has a 16bit size field, hence that appears to
  61  * be the absolute maximum. */
  62 #define DNS_PACKET_SIZE_MAX 0xFFFFu
  63
  64 /* The default size to use for allocation when we don't know how large
  65  * the packet will turn out to be. */
  66 #define DNS_PACKET_SIZE_START 512u
  67
  68 /* RFC 1035 say 512 is the maximum, for classic unicast DNS */
  69 #define DNS_PACKET_UNICAST_SIZE_MAX 512u
  70
  71 /* With EDNS0 we can use larger packets, default to 4096, which is what is commonly used */
  72 #define DNS_PACKET_UNICAST_SIZE_LARGE_MAX 4096u
  73
  74 struct DnsPacket {
  75         int n_ref;
  76         DnsProtocol protocol;
  77         size_t size, allocated, rindex, max_size;
  78         void *_data; /* don't access directly, use DNS_PACKET_DATA()! */
  79         Hashmap *names; /* For name compression */
  80         size_t opt_start, opt_size;
  81
  82         /* Parsed data */
  83         DnsQuestion *question;
  84         DnsAnswer *answer;
  85         DnsResourceRecord *opt;
  86
  87         /* Packet reception metadata */
  88         int ifindex;
  89         int family, ipproto;
  90         union in_addr_union sender, destination;
  91         uint16_t sender_port, destination_port;
  92         uint32_t ttl;
  93
  94         /* For support of truncated packets */
  95         DnsPacket *more;
  96
  97         bool on_stack:1;
  98         bool extracted:1;
  99         bool refuse_compression:1;
 100         bool canonical_form:1;
 101 };
 102
 103 static inline uint8_t* DNS_PACKET_DATA(DnsPacket *p) {
 104         if (_unlikely_(!p))
 105                 return NULL;
 106
 107         if (p->_data)
 108                 return p->_data;
 109
 110         return ((uint8_t*) p) + ALIGN(sizeof(DnsPacket));
 111 }
 112
 113 #define DNS_PACKET_HEADER(p) ((DnsPacketHeader*) DNS_PACKET_DATA(p))
 114 #define DNS_PACKET_ID(p) DNS_PACKET_HEADER(p)->id
 115 #define DNS_PACKET_QR(p) ((be16toh(DNS_PACKET_HEADER(p)->flags) >> 15) & 1)
 116 #define DNS_PACKET_OPCODE(p) ((be16toh(DNS_PACKET_HEADER(p)->flags) >> 11) & 15)
 117 #define DNS_PACKET_AA(p) ((be16toh(DNS_PACKET_HEADER(p)->flags) >> 10) & 1)
 118 #define DNS_PACKET_TC(p) ((be16toh(DNS_PACKET_HEADER(p)->flags) >> 9) & 1)
 119 #define DNS_PACKET_RD(p) ((be16toh(DNS_PACKET_HEADER(p)->flags) >> 8) & 1)
 120 #define DNS_PACKET_RA(p) ((be16toh(DNS_PACKET_HEADER(p)->flags) >> 7) & 1)
 121 #define DNS_PACKET_AD(p) ((be16toh(DNS_PACKET_HEADER(p)->flags) >> 5) & 1)
 122 #define DNS_PACKET_CD(p) ((be16toh(DNS_PACKET_HEADER(p)->flags) >> 4) & 1)
 123
 124 #define DNS_PACKET_FLAG_TC (UINT16_C(1) << 9)
 125
 126 static inline uint16_t DNS_PACKET_RCODE(DnsPacket *p) {
 127         uint16_t rcode;
 128
 129         if (p->opt)
 130                 rcode = (uint16_t) (p->opt->ttl >> 24);
 131         else
 132                 rcode = 0;
 133
 134         return rcode | (be16toh(DNS_PACKET_HEADER(p)->flags) & 0xF);
 135 }
 136
 137 static inline uint16_t DNS_PACKET_PAYLOAD_SIZE_MAX(DnsPacket *p) {
 138
 139         /* Returns the advertised maximum datagram size for replies, or the DNS default if there's nothing defined. */
 140
 141         if (p->opt)
 142                 return MAX(DNS_PACKET_UNICAST_SIZE_MAX, p->opt->key->class);
 143
 144         return DNS_PACKET_UNICAST_SIZE_MAX;
 145 }
 146
 147 static inline bool DNS_PACKET_DO(DnsPacket *p) {
 148         if (!p->opt)
 149                 return false;
 150
 151         return !!(p->opt->ttl & (1U << 15));
 152 }
 153
 154 static inline bool DNS_PACKET_VERSION_SUPPORTED(DnsPacket *p) {
 155         /* Returns true if this packet is in a version we support. Which means either non-EDNS or EDNS(0), but not EDNS
 156          * of any newer versions */
 157
 158         if (!p->opt)
 159                 return true;
 160
 161         return DNS_RESOURCE_RECORD_OPT_VERSION_SUPPORTED(p->opt);
 162 }
 163
 164 /* LLMNR defines some bits differently */
 165 #define DNS_PACKET_LLMNR_C(p) DNS_PACKET_AA(p)
 166 #define DNS_PACKET_LLMNR_T(p) DNS_PACKET_RD(p)
 167
 168 #define DNS_PACKET_QDCOUNT(p) be16toh(DNS_PACKET_HEADER(p)->qdcount)
 169 #define DNS_PACKET_ANCOUNT(p) be16toh(DNS_PACKET_HEADER(p)->ancount)
 170 #define DNS_PACKET_NSCOUNT(p) be16toh(DNS_PACKET_HEADER(p)->nscount)
 171 #define DNS_PACKET_ARCOUNT(p) be16toh(DNS_PACKET_HEADER(p)->arcount)
 172
 173 #define DNS_PACKET_MAKE_FLAGS(qr, opcode, aa, tc, rd, ra, ad, cd, rcode) \
 174         (((uint16_t) !!(qr) << 15) |                                    \
 175          ((uint16_t) ((opcode) & 15) << 11) |                           \
 176          ((uint16_t) !!(aa) << 10) |                /* on LLMNR: c */   \
 177          ((uint16_t) !!(tc) << 9) |                                     \
 178          ((uint16_t) !!(rd) << 8) |                 /* on LLMNR: t */   \
 179          ((uint16_t) !!(ra) << 7) |                                     \
 180          ((uint16_t) !!(ad) << 5) |                                     \
 181          ((uint16_t) !!(cd) << 4) |                                     \
 182          ((uint16_t) ((rcode) & 15)))
 183
 184 static inline unsigned DNS_PACKET_RRCOUNT(DnsPacket *p) {
 185         return
 186                 (unsigned) DNS_PACKET_ANCOUNT(p) +
 187                 (unsigned) DNS_PACKET_NSCOUNT(p) +
 188                 (unsigned) DNS_PACKET_ARCOUNT(p);
 189 }
 190
 191 int dns_packet_new(DnsPacket **p, DnsProtocol protocol, size_t min_alloc_dsize, size_t max_size);
 192 int dns_packet_new_query(DnsPacket **p, DnsProtocol protocol, size_t min_alloc_dsize, bool dnssec_checking_disabled);
 193
 194 void dns_packet_set_flags(DnsPacket *p, bool dnssec_checking_disabled, bool truncated);
 195
 196 DnsPacket *dns_packet_ref(DnsPacket *p);
 197 DnsPacket *dns_packet_unref(DnsPacket *p);
 198
 199 DEFINE_TRIVIAL_CLEANUP_FUNC(DnsPacket*, dns_packet_unref);
 200
 201 int dns_packet_validate(DnsPacket *p);
 202 int dns_packet_validate_reply(DnsPacket *p);
 203 int dns_packet_validate_query(DnsPacket *p);
 204
 205 int dns_packet_is_reply_for(DnsPacket *p, const DnsResourceKey *key);
 206
 207 int dns_packet_append_blob(DnsPacket *p, const void *d, size_t sz, size_t *start);
 208 int dns_packet_append_uint8(DnsPacket *p, uint8_t v, size_t *start);
 209 int dns_packet_append_uint16(DnsPacket *p, uint16_t v, size_t *start);
 210 int dns_packet_append_uint32(DnsPacket *p, uint32_t v, size_t *start);
 211 int dns_packet_append_string(DnsPacket *p, const char *s, size_t *start);
 212 int dns_packet_append_raw_string(DnsPacket *p, const void *s, size_t size, size_t *start);
 213 int dns_packet_append_label(DnsPacket *p, const char *s, size_t l, bool canonical_candidate, size_t *start);
 214 int dns_packet_append_name(DnsPacket *p, const char *name, bool allow_compression, bool canonical_candidate, size_t *start);
 215 int dns_packet_append_key(DnsPacket *p, const DnsResourceKey *key, const DnsAnswerFlags flags, size_t *start);
 216 int dns_packet_append_rr(DnsPacket *p, const DnsResourceRecord *rr, const DnsAnswerFlags flags, size_t *start, size_t *rdata_start);
 217 int dns_packet_append_opt(DnsPacket *p, uint16_t max_udp_size, bool edns0_do, int rcode, size_t *start);
 218 int dns_packet_append_question(DnsPacket *p, DnsQuestion *q);
 219 int dns_packet_append_answer(DnsPacket *p, DnsAnswer *a);
 220
 221 void dns_packet_truncate(DnsPacket *p, size_t sz);
 222 int dns_packet_truncate_opt(DnsPacket *p);
 223
 224 int dns_packet_read(DnsPacket *p, size_t sz, const void **ret, size_t *start);
 225 int dns_packet_read_blob(DnsPacket *p, void *d, size_t sz, size_t *start);
 226 int dns_packet_read_uint8(DnsPacket *p, uint8_t *ret, size_t *start);
 227 int dns_packet_read_uint16(DnsPacket *p, uint16_t *ret, size_t *start);
 228 int dns_packet_read_uint32(DnsPacket *p, uint32_t *ret, size_t *start);
 229 int dns_packet_read_string(DnsPacket *p, char **ret, size_t *start);
 230 int dns_packet_read_raw_string(DnsPacket *p, const void **ret, size_t *size, size_t *start);
 231 int dns_packet_read_name(DnsPacket *p, char **ret, bool allow_compression, size_t *start);
 232 int dns_packet_read_key(DnsPacket *p, DnsResourceKey **ret, bool *ret_cache_flush, size_t *start);
 233 int dns_packet_read_rr(DnsPacket *p, DnsResourceRecord **ret, bool *ret_cache_flush, size_t *start);
 234
 235 void dns_packet_rewind(DnsPacket *p, size_t idx);
 236
 237 int dns_packet_skip_question(DnsPacket *p);
 238 int dns_packet_extract(DnsPacket *p);
 239
 240 static inline bool DNS_PACKET_SHALL_CACHE(DnsPacket *p) {
 241         /* Never cache data originating from localhost, under the
 242          * assumption, that it's coming from a locally DNS forwarder
 243          * or server, that is caching on its own. */
 244
 245         return in_addr_is_localhost(p->family, &p->sender) == 0;
 246 }
 247
 248 /* https://www.iana.org/assignments/dns-parameters/dns-parameters.xhtml#dns-parameters-6 */
 249 enum {
 250         DNS_RCODE_SUCCESS = 0,
 251         DNS_RCODE_FORMERR = 1,
 252         DNS_RCODE_SERVFAIL = 2,
 253         DNS_RCODE_NXDOMAIN = 3,
 254         DNS_RCODE_NOTIMP = 4,
 255         DNS_RCODE_REFUSED = 5,
 256         DNS_RCODE_YXDOMAIN = 6,
 257         DNS_RCODE_YXRRSET = 7,
 258         DNS_RCODE_NXRRSET = 8,
 259         DNS_RCODE_NOTAUTH = 9,
 260         DNS_RCODE_NOTZONE = 10,
 261         DNS_RCODE_BADVERS = 16,
 262         DNS_RCODE_BADSIG = 16, /* duplicate value! */
 263         DNS_RCODE_BADKEY = 17,
 264         DNS_RCODE_BADTIME = 18,
 265         DNS_RCODE_BADMODE = 19,
 266         DNS_RCODE_BADNAME = 20,
 267         DNS_RCODE_BADALG = 21,
 268         DNS_RCODE_BADTRUNC = 22,
 269         DNS_RCODE_BADCOOKIE = 23,
 270         _DNS_RCODE_MAX_DEFINED,
 271         _DNS_RCODE_MAX = 4095 /* 4 bit rcode in the header plus 8 bit rcode in OPT, makes 12 bit */
 272 };
 273
 274 const char* dns_rcode_to_string(int i) _const_;
 275 int dns_rcode_from_string(const char *s) _pure_;
 276
 277 const char* dns_protocol_to_string(DnsProtocol p) _const_;
 278 DnsProtocol dns_protocol_from_string(const char *s) _pure_;
 279
 280 #define LLMNR_MULTICAST_IPV4_ADDRESS ((struct in_addr) { .s_addr = htobe32(224U << 24 | 252U) })
 281 #define LLMNR_MULTICAST_IPV6_ADDRESS ((struct in6_addr) { .s6_addr = { 0xFF, 0x02, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x01, 0x00, 0x03 } })
 282
 283 #define MDNS_MULTICAST_IPV4_ADDRESS  ((struct in_addr) { .s_addr = htobe32(224U << 24 | 251U) })
 284 #define MDNS_MULTICAST_IPV6_ADDRESS  ((struct in6_addr) { .s6_addr = { 0xFF, 0x02, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0xfb } })
 285
 286 static inline uint64_t SD_RESOLVED_FLAGS_MAKE(DnsProtocol protocol, int family, bool authenticated) {
 287         uint64_t f;
 288
 289         /* Converts a protocol + family into a flags field as used in queries and responses */
 290
 291         f = authenticated ? SD_RESOLVED_AUTHENTICATED : 0;
 292
 293         switch (protocol) {
 294         case DNS_PROTOCOL_DNS:
 295                 return f|SD_RESOLVED_DNS;
 296
 297         case DNS_PROTOCOL_LLMNR:
 298                 return f|(family == AF_INET6 ? SD_RESOLVED_LLMNR_IPV6 : SD_RESOLVED_LLMNR_IPV4);
 299
 300         case DNS_PROTOCOL_MDNS:
 301                 return f|(family == AF_INET6 ? SD_RESOLVED_MDNS_IPV6 : SD_RESOLVED_MDNS_IPV4);
 302
 303         default:
 304                 return f;
 305         }
 306 }
 307
 308 static inline size_t dns_packet_size_max(DnsPacket *p) {
 309         assert(p);
 310
 311         /* Why not insist on a fully initialized max_size during DnsPacket construction? Well, this way it's easy to
 312          * allocate a transient, throw-away DnsPacket on the stack by simple zero initialization, without having to
 313          * deal with explicit field initialization. */
 314
 315         return p->max_size != 0 ? p->max_size : DNS_PACKET_SIZE_MAX;
 316 }