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