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