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