src/network/lookup_name.c

   1 #include <sys/socket.h>
   2 #include <netinet/in.h>
   3 #include <netdb.h>
   4 #include <net/if.h>
   5 #include <arpa/inet.h>
   6 #include <ctype.h>
   7 #include <stdlib.h>
   8 #include <string.h>
   9 #include <fcntl.h>
  10 #include <unistd.h>
  11 #include <pthread.h>
  12 #include <errno.h>
  13 #include <resolv.h>
  14 #include "lookup.h"
  15 #include "stdio_impl.h"
  16 #include "syscall.h"
  17
  18 static int is_valid_hostname(const char *host)
  19 {
  20         const unsigned char *s;
  21         if (strnlen(host, 255)-1 >= 254 || mbstowcs(0, host, 0) == -1) return 0;
  22         for (s=(void *)host; *s>=0x80 || *s=='.' || *s=='-' || isalnum(*s); s++);
  23         return !*s;
  24 }
  25
  26 static int name_from_null(struct address buf[static 2], const char *name, int family, int flags)
  27 {
  28         int cnt = 0;
  29         if (name) return 0;
  30         if (flags & AI_PASSIVE) {
  31                 if (family != AF_INET6)
  32                         buf[cnt++] = (struct address){ .family = AF_INET };
  33                 if (family != AF_INET)
  34                         buf[cnt++] = (struct address){ .family = AF_INET6 };
  35         } else {
  36                 if (family != AF_INET6)
  37                         buf[cnt++] = (struct address){ .family = AF_INET, .addr = { 127,0,0,1 } };
  38                 if (family != AF_INET)
  39                         buf[cnt++] = (struct address){ .family = AF_INET6, .addr = { [15] = 1 } };
  40         }
  41         return cnt;
  42 }
  43
  44 static int name_from_numeric(struct address buf[static 1], const char *name, int family)
  45 {
  46         return __lookup_ipliteral(buf, name, family);
  47 }
  48
  49 static int name_from_hosts(struct address buf[static MAXADDRS], char canon[static 256], const char *name, int family)
  50 {
  51         char line[512];
  52         size_t l = strlen(name);
  53         int cnt = 0, badfam = 0, have_canon = 0;
  54         unsigned char _buf[1032];
  55         FILE _f, *f = __fopen_rb_ca("/etc/hosts", &_f, _buf, sizeof _buf);
  56         if (!f) switch (errno) {
  57         case ENOENT:
  58         case ENOTDIR:
  59         case EACCES:
  60                 return 0;
  61         default:
  62                 return EAI_SYSTEM;
  63         }
  64         while (fgets(line, sizeof line, f) && cnt < MAXADDRS) {
  65                 char *p, *z;
  66
  67                 if ((p=strchr(line, '#'))) *p++='\n', *p=0;
  68                 for(p=line+1; (p=strstr(p, name)) &&
  69                         (!isspace(p[-1]) || !isspace(p[l])); p++);
  70                 if (!p) continue;
  71
  72                 /* Isolate IP address to parse */
  73                 for (p=line; *p && !isspace(*p); p++);
  74                 *p++ = 0;
  75                 switch (name_from_numeric(buf+cnt, line, family)) {
  76                 case 1:
  77                         cnt++;
  78                         break;
  79                 case 0:
  80                         continue;
  81                 default:
  82                         badfam = EAI_NODATA;
  83                         break;
  84                 }
  85
  86                 if (have_canon) continue;
  87
  88                 /* Extract first name as canonical name */
  89                 for (; *p && isspace(*p); p++);
  90                 for (z=p; *z && !isspace(*z); z++);
  91                 *z = 0;
  92                 if (is_valid_hostname(p)) {
  93                         have_canon = 1;
  94                         memcpy(canon, p, z-p+1);
  95                 }
  96         }
  97         __fclose_ca(f);
  98         return cnt ? cnt : badfam;
  99 }
 100
 101 struct dpc_ctx {
 102         struct address *addrs;
 103         char *canon;
 104         int cnt;
 105         int rrtype;
 106 };
 107
 108 #define RR_A 1
 109 #define RR_CNAME 5
 110 #define RR_AAAA 28
 111
 112 #define ABUF_SIZE 4800
 113
 114 static int dns_parse_callback(void *c, int rr, const void *data, int len, const void *packet, int plen)
 115 {
 116         char tmp[256];
 117         int family;
 118         struct dpc_ctx *ctx = c;
 119         if (rr == RR_CNAME) {
 120                 if (__dn_expand(packet, (const unsigned char *)packet + plen,
 121                     data, tmp, sizeof tmp) > 0 && is_valid_hostname(tmp))
 122                         strcpy(ctx->canon, tmp);
 123                 return 0;
 124         }
 125         if (ctx->cnt >= MAXADDRS) return 0;
 126         if (rr != ctx->rrtype) return 0;
 127         switch (rr) {
 128         case RR_A:
 129                 if (len != 4) return -1;
 130                 family = AF_INET;
 131                 break;
 132         case RR_AAAA:
 133                 if (len != 16) return -1;
 134                 family = AF_INET6;
 135                 break;
 136         }
 137         ctx->addrs[ctx->cnt].family = family;
 138         ctx->addrs[ctx->cnt].scopeid = 0;
 139         memcpy(ctx->addrs[ctx->cnt++].addr, data, len);
 140         return 0;
 141 }
 142
 143 static int name_from_dns(struct address buf[static MAXADDRS], char canon[static 256], const char *name, int family, const struct resolvconf *conf)
 144 {
 145         unsigned char qbuf[2][280], abuf[2][ABUF_SIZE];
 146         const unsigned char *qp[2] = { qbuf[0], qbuf[1] };
 147         unsigned char *ap[2] = { abuf[0], abuf[1] };
 148         int qlens[2], alens[2], qtypes[2];
 149         int i, nq = 0;
 150         struct dpc_ctx ctx = { .addrs = buf, .canon = canon };
 151         static const struct { int af; int rr; } afrr[2] = {
 152                 { .af = AF_INET6, .rr = RR_A },
 153                 { .af = AF_INET, .rr = RR_AAAA },
 154         };
 155
 156         for (i=0; i<2; i++) {
 157                 if (family != afrr[i].af) {
 158                         qlens[nq] = __res_mkquery(0, name, 1, afrr[i].rr,
 159                                 0, 0, 0, qbuf[nq], sizeof *qbuf);
 160                         if (qlens[nq] == -1)
 161                                 return 0;
 162                         qtypes[nq] = afrr[i].rr;
 163                         qbuf[nq][3] = 0; /* don't need AD flag */
 164                         /* Ensure query IDs are distinct. */
 165                         if (nq && qbuf[nq][0] == qbuf[0][0])
 166                                 qbuf[nq][0]++;
 167                         nq++;
 168                 }
 169         }
 170
 171         if (__res_msend_rc(nq, qp, qlens, ap, alens, sizeof *abuf, conf) < 0)
 172                 return EAI_SYSTEM;
 173
 174         for (i=0; i<nq; i++) {
 175                 if (alens[i] < 4 || (abuf[i][3] & 15) == 2) return EAI_AGAIN;
 176                 if ((abuf[i][3] & 15) == 3) return 0;
 177                 if ((abuf[i][3] & 15) != 0) return EAI_FAIL;
 178         }
 179
 180         for (i=nq-1; i>=0; i--) {
 181                 ctx.rrtype = qtypes[i];
 182                 if (alens[i] > sizeof(abuf[i])) alens[i] = sizeof abuf[i];
 183                 __dns_parse(abuf[i], alens[i], dns_parse_callback, &ctx);
 184         }
 185
 186         if (ctx.cnt) return ctx.cnt;
 187         return EAI_NODATA;
 188 }
 189
 190 static int name_from_dns_search(struct address buf[static MAXADDRS], char canon[static 256], const char *name, int family)
 191 {
 192         char search[256];
 193         struct resolvconf conf;
 194         size_t l, dots;
 195         char *p, *z;
 196
 197         if (__get_resolv_conf(&conf, search, sizeof search) < 0) return -1;
 198
 199         /* Count dots, suppress search when >=ndots or name ends in
 200          * a dot, which is an explicit request for global scope. */
 201         for (dots=l=0; name[l]; l++) if (name[l]=='.') dots++;
 202         if (dots >= conf.ndots || name[l-1]=='.') *search = 0;
 203
 204         /* Strip final dot for canon, fail if multiple trailing dots. */
 205         if (name[l-1]=='.') l--;
 206         if (!l || name[l-1]=='.') return EAI_NONAME;
 207
 208         /* This can never happen; the caller already checked length. */
 209         if (l >= 256) return EAI_NONAME;
 210
 211         /* Name with search domain appended is setup in canon[]. This both
 212          * provides the desired default canonical name (if the requested
 213          * name is not a CNAME record) and serves as a buffer for passing
 214          * the full requested name to name_from_dns. */
 215         memcpy(canon, name, l);
 216         canon[l] = '.';
 217
 218         for (p=search; *p; p=z) {
 219                 for (; isspace(*p); p++);
 220                 for (z=p; *z && !isspace(*z); z++);
 221                 if (z==p) break;
 222                 if (z-p < 256 - l - 1) {
 223                         memcpy(canon+l+1, p, z-p);
 224                         canon[z-p+1+l] = 0;
 225                         int cnt = name_from_dns(buf, canon, canon, family, &conf);
 226                         if (cnt) return cnt;
 227                 }
 228         }
 229
 230         canon[l] = 0;
 231         return name_from_dns(buf, canon, name, family, &conf);
 232 }
 233
 234 static const struct policy {
 235         unsigned char addr[16];
 236         unsigned char len, mask;
 237         unsigned char prec, label;
 238 } defpolicy[] = {
 239         { "\0\0\0\0\0\0\0\0\0\0\0\0\0\0\0\1", 15, 0xff, 50, 0 },
 240         { "\0\0\0\0\0\0\0\0\0\0\xff\xff", 11, 0xff, 35, 4 },
 241         { "\x20\2", 1, 0xff, 30, 2 },
 242         { "\x20\1", 3, 0xff, 5, 5 },
 243         { "\xfc", 0, 0xfe, 3, 13 },
 244 #if 0
 245         /* These are deprecated and/or returned to the address
 246          * pool, so despite the RFC, treating them as special
 247          * is probably wrong. */
 248         { "", 11, 0xff, 1, 3 },
 249         { "\xfe\xc0", 1, 0xc0, 1, 11 },
 250         { "\x3f\xfe", 1, 0xff, 1, 12 },
 251 #endif
 252         /* Last rule must match all addresses to stop loop. */
 253         { "", 0, 0, 40, 1 },
 254 };
 255
 256 static const struct policy *policyof(const struct in6_addr *a)
 257 {
 258         int i;
 259         for (i=0; ; i++) {
 260                 if (memcmp(a->s6_addr, defpolicy[i].addr, defpolicy[i].len))
 261                         continue;
 262                 if ((a->s6_addr[defpolicy[i].len] & defpolicy[i].mask)
 263                     != defpolicy[i].addr[defpolicy[i].len])
 264                         continue;
 265                 return defpolicy+i;
 266         }
 267 }
 268
 269 static int labelof(const struct in6_addr *a)
 270 {
 271         return policyof(a)->label;
 272 }
 273
 274 static int scopeof(const struct in6_addr *a)
 275 {
 276         if (IN6_IS_ADDR_MULTICAST(a)) return a->s6_addr[1] & 15;
 277         if (IN6_IS_ADDR_LINKLOCAL(a)) return 2;
 278         if (IN6_IS_ADDR_LOOPBACK(a)) return 2;
 279         if (IN6_IS_ADDR_SITELOCAL(a)) return 5;
 280         return 14;
 281 }
 282
 283 static int prefixmatch(const struct in6_addr *s, const struct in6_addr *d)
 284 {
 285         /* FIXME: The common prefix length should be limited to no greater
 286          * than the nominal length of the prefix portion of the source
 287          * address. However the definition of the source prefix length is
 288          * not clear and thus this limiting is not yet implemented. */
 289         unsigned i;
 290         for (i=0; i<128 && !((s->s6_addr[i/8]^d->s6_addr[i/8])&(128>>(i%8))); i++);
 291         return i;
 292 }
 293
 294 #define DAS_USABLE              0x40000000
 295 #define DAS_MATCHINGSCOPE       0x20000000
 296 #define DAS_MATCHINGLABEL       0x10000000
 297 #define DAS_PREC_SHIFT          20
 298 #define DAS_SCOPE_SHIFT         16
 299 #define DAS_PREFIX_SHIFT        8
 300 #define DAS_ORDER_SHIFT         0
 301
 302 static int addrcmp(const void *_a, const void *_b)
 303 {
 304         const struct address *a = _a, *b = _b;
 305         return b->sortkey - a->sortkey;
 306 }
 307
 308 int __lookup_name(struct address buf[static MAXADDRS], char canon[static 256], const char *name, int family, int flags)
 309 {
 310         int cnt = 0, i, j;
 311
 312         *canon = 0;
 313         if (name) {
 314                 /* reject empty name and check len so it fits into temp bufs */
 315                 size_t l = strnlen(name, 255);
 316                 if (l-1 >= 254)
 317                         return EAI_NONAME;
 318                 memcpy(canon, name, l+1);
 319         }
 320
 321         /* Procedurally, a request for v6 addresses with the v4-mapped
 322          * flag set is like a request for unspecified family, followed
 323          * by filtering of the results. */
 324         if (flags & AI_V4MAPPED) {
 325                 if (family == AF_INET6) family = AF_UNSPEC;
 326                 else flags -= AI_V4MAPPED;
 327         }
 328
 329         /* Try each backend until there's at least one result. */
 330         cnt = name_from_null(buf, name, family, flags);
 331         if (!cnt) cnt = name_from_numeric(buf, name, family);
 332         if (!cnt && !(flags & AI_NUMERICHOST)) {
 333                 cnt = name_from_hosts(buf, canon, name, family);
 334                 if (!cnt) cnt = name_from_dns_search(buf, canon, name, family);
 335         }
 336         if (cnt<=0) return cnt ? cnt : EAI_NONAME;
 337
 338         /* Filter/transform results for v4-mapped lookup, if requested. */
 339         if (flags & AI_V4MAPPED) {
 340                 if (!(flags & AI_ALL)) {
 341                         /* If any v6 results exist, remove v4 results. */
 342                         for (i=0; i<cnt && buf[i].family != AF_INET6; i++);
 343                         if (i<cnt) {
 344                                 for (j=0; i<cnt; i++) {
 345                                         if (buf[i].family == AF_INET6)
 346                                                 buf[j++] = buf[i];
 347                                 }
 348                                 cnt = i = j;
 349                         }
 350                 }
 351                 /* Translate any remaining v4 results to v6 */
 352                 for (i=0; i<cnt; i++) {
 353                         if (buf[i].family != AF_INET) continue;
 354                         memcpy(buf[i].addr+12, buf[i].addr, 4);
 355                         memcpy(buf[i].addr, "\0\0\0\0\0\0\0\0\0\0\xff\xff", 12);
 356                         buf[i].family = AF_INET6;
 357                 }
 358         }
 359
 360         /* No further processing is needed if there are fewer than 2
 361          * results or if there are only IPv4 results. */
 362         if (cnt<2 || family==AF_INET) return cnt;
 363         for (i=0; i<cnt; i++) if (buf[i].family != AF_INET) break;
 364         if (i==cnt) return cnt;
 365
 366         int cs;
 367         pthread_setcancelstate(PTHREAD_CANCEL_DISABLE, &cs);
 368
 369         /* The following implements a subset of RFC 3484/6724 destination
 370          * address selection by generating a single 31-bit sort key for
 371          * each address. Rules 3, 4, and 7 are omitted for having
 372          * excessive runtime and code size cost and dubious benefit.
 373          * So far the label/precedence table cannot be customized. */
 374         for (i=0; i<cnt; i++) {
 375                 int family = buf[i].family;
 376                 int key = 0;
 377                 struct sockaddr_in6 sa6 = { 0 }, da6 = {
 378                         .sin6_family = AF_INET6,
 379                         .sin6_scope_id = buf[i].scopeid,
 380                         .sin6_port = 65535
 381                 };
 382                 struct sockaddr_in sa4 = { 0 }, da4 = {
 383                         .sin_family = AF_INET,
 384                         .sin_port = 65535
 385                 };
 386                 void *sa, *da;
 387                 socklen_t salen, dalen;
 388                 if (family == AF_INET6) {
 389                         memcpy(da6.sin6_addr.s6_addr, buf[i].addr, 16);
 390                         da = &da6; dalen = sizeof da6;
 391                         sa = &sa6; salen = sizeof sa6;
 392                 } else {
 393                         memcpy(sa6.sin6_addr.s6_addr,
 394                                 "\0\0\0\0\0\0\0\0\0\0\xff\xff", 12);
 395                         memcpy(da6.sin6_addr.s6_addr+12, buf[i].addr, 4);
 396                         memcpy(da6.sin6_addr.s6_addr,
 397                                 "\0\0\0\0\0\0\0\0\0\0\xff\xff", 12);
 398                         memcpy(da6.sin6_addr.s6_addr+12, buf[i].addr, 4);
 399                         memcpy(&da4.sin_addr, buf[i].addr, 4);
 400                         da = &da4; dalen = sizeof da4;
 401                         sa = &sa4; salen = sizeof sa4;
 402                 }
 403                 const struct policy *dpolicy = policyof(&da6.sin6_addr);
 404                 int dscope = scopeof(&da6.sin6_addr);
 405                 int dlabel = dpolicy->label;
 406                 int dprec = dpolicy->prec;
 407                 int prefixlen = 0;
 408                 int fd = socket(family, SOCK_DGRAM|SOCK_CLOEXEC, IPPROTO_UDP);
 409                 if (fd >= 0) {
 410                         if (!connect(fd, da, dalen)) {
 411                                 key |= DAS_USABLE;
 412                                 if (!getsockname(fd, sa, &salen)) {
 413                                         if (family == AF_INET) memcpy(
 414                                                 sa6.sin6_addr.s6_addr+12,
 415                                                 &sa4.sin_addr, 4);
 416                                         if (dscope == scopeof(&sa6.sin6_addr))
 417                                                 key |= DAS_MATCHINGSCOPE;
 418                                         if (dlabel == labelof(&sa6.sin6_addr))
 419                                                 key |= DAS_MATCHINGLABEL;
 420                                         prefixlen = prefixmatch(&sa6.sin6_addr,
 421                                                 &da6.sin6_addr);
 422                                 }
 423                         }
 424                         close(fd);
 425                 }
 426                 key |= dprec << DAS_PREC_SHIFT;
 427                 key |= (15-dscope) << DAS_SCOPE_SHIFT;
 428                 key |= prefixlen << DAS_PREFIX_SHIFT;
 429                 key |= (MAXADDRS-i) << DAS_ORDER_SHIFT;
 430                 buf[i].sortkey = key;
 431         }
 432         qsort(buf, cnt, sizeof *buf, addrcmp);
 433
 434         pthread_setcancelstate(cs, 0);
 435
 436         return cnt;
 437 }