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;
  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                 if (name_from_numeric(buf+cnt, line, family))
  75                         cnt++;
  76
  77                 /* Extract first name as canonical name */
  78                 for (; *p && isspace(*p); p++);
  79                 for (z=p; *z && !isspace(*z); z++);
  80                 *z = 0;
  81                 if (is_valid_hostname(p)) memcpy(canon, p, z-p+1);
  82         }
  83         __fclose_ca(f);
  84         return cnt;
  85 }
  86
  87 struct dpc_ctx {
  88         struct address *addrs;
  89         char *canon;
  90         int cnt;
  91 };
  92
  93 int __dns_parse(const unsigned char *, int, int (*)(void *, int, const void *, int, const void *), void *);
  94 int __dn_expand(const unsigned char *, const unsigned char *, const unsigned char *, char *, int);
  95 int __res_mkquery(int, const char *, int, int, const unsigned char *, int, const unsigned char*, unsigned char *, int);
  96 int __res_msend(int, const unsigned char *const *, const int *, unsigned char *const *, int *, int);
  97
  98 #define RR_A 1
  99 #define RR_CNAME 5
 100 #define RR_AAAA 28
 101
 102 static int dns_parse_callback(void *c, int rr, const void *data, int len, const void *packet)
 103 {
 104         char tmp[256];
 105         struct dpc_ctx *ctx = c;
 106         switch (rr) {
 107         case RR_A:
 108                 if (len != 4) return -1;
 109                 ctx->addrs[ctx->cnt].family = AF_INET;
 110                 ctx->addrs[ctx->cnt].scopeid = 0;
 111                 memcpy(ctx->addrs[ctx->cnt++].addr, data, 4);
 112                 break;
 113         case RR_AAAA:
 114                 if (len != 16) return -1;
 115                 ctx->addrs[ctx->cnt].family = AF_INET6;
 116                 ctx->addrs[ctx->cnt].scopeid = 0;
 117                 memcpy(ctx->addrs[ctx->cnt++].addr, data, 16);
 118                 break;
 119         case RR_CNAME:
 120                 if (__dn_expand(packet, (const unsigned char *)packet + 512,
 121                     data, tmp, sizeof tmp) > 0 && is_valid_hostname(tmp))
 122                         strcpy(ctx->canon, tmp);
 123                 break;
 124         }
 125         return 0;
 126 }
 127
 128 static int name_from_dns(struct address buf[static MAXADDRS], char canon[static 256], const char *name, int family)
 129 {
 130         unsigned char qbuf[2][280], abuf[2][512];
 131         const unsigned char *qp[2] = { qbuf[0], qbuf[1] };
 132         unsigned char *ap[2] = { abuf[0], abuf[1] };
 133         int qlens[2], alens[2];
 134         int i, nq = 0;
 135         struct dpc_ctx ctx = { .addrs = buf, .canon = canon };
 136
 137         if (family != AF_INET6) {
 138                 qlens[nq] = __res_mkquery(0, name, 1, RR_A, 0, 0, 0,
 139                         qbuf[nq], sizeof *qbuf);
 140                 nq++;
 141         }
 142         if (family != AF_INET) {
 143                 qlens[nq] = __res_mkquery(0, name, 1, RR_AAAA, 0, 0, 0,
 144                         qbuf[nq], sizeof *qbuf);
 145                 nq++;
 146         }
 147
 148         if (__res_msend(nq, qp, qlens, ap, alens, sizeof *abuf) < 0) return EAI_SYSTEM;
 149
 150         for (i=0; i<nq; i++)
 151                 __dns_parse(abuf[i], alens[i], dns_parse_callback, &ctx);
 152
 153         if (ctx.cnt) return ctx.cnt;
 154         if (alens[0] < 4 || (abuf[0][3] & 15) == 2) return EAI_AGAIN;
 155         if ((abuf[0][3] & 15) == 3) return EAI_NONAME;
 156         return EAI_FAIL;
 157 }
 158
 159 static const struct policy {
 160         unsigned char addr[16];
 161         unsigned char len, mask;
 162         unsigned char prec, label;
 163 } defpolicy[] = {
 164         { "\0\0\0\0\0\0\0\0\0\0\0\0\0\0\0\1", 15, 0xff, 50, 0 },
 165         { "\0\0\0\0\0\0\0\0\0\0\xff\xff", 11, 0xff, 35, 4 },
 166         { "\x20\2", 1, 0xff, 30, 2 },
 167         { "\x20\1", 3, 0xff, 5, 5 },
 168         { "\xfc", 0, 0xfe, 3, 13 },
 169 #if 0
 170         /* These are deprecated and/or returned to the address
 171          * pool, so despite the RFC, treating them as special
 172          * is probably wrong. */
 173         { "", 11, 0xff, 1, 3 },
 174         { "\xfe\xc0", 1, 0xc0, 1, 11 },
 175         { "\x3f\xfe", 1, 0xff, 1, 12 },
 176 #endif
 177         /* Last rule must match all addresses to stop loop. */
 178         { "", 0, 0, 40, 1 },
 179 };
 180
 181 static const struct policy *policyof(const struct in6_addr *a)
 182 {
 183         int i;
 184         for (i=0; ; i++) {
 185                 if (memcmp(a->s6_addr, defpolicy[i].addr, defpolicy[i].len))
 186                         continue;
 187                 if ((a->s6_addr[defpolicy[i].len] & defpolicy[i].mask)
 188                     != defpolicy[i].addr[defpolicy[i].len])
 189                         continue;
 190                 return defpolicy+i;
 191         }
 192 }
 193
 194 static int labelof(const struct in6_addr *a)
 195 {
 196         return policyof(a)->label;
 197 }
 198
 199 static int scopeof(const struct in6_addr *a)
 200 {
 201         if (IN6_IS_ADDR_MULTICAST(a)) return a->s6_addr[1] & 15;
 202         if (IN6_IS_ADDR_LINKLOCAL(a)) return 2;
 203         if (IN6_IS_ADDR_LOOPBACK(a)) return 2;
 204         if (IN6_IS_ADDR_SITELOCAL(a)) return 5;
 205         return 14;
 206 }
 207
 208 static int prefixmatch(const struct in6_addr *s, const struct in6_addr *d)
 209 {
 210         /* FIXME: The common prefix length should be limited to no greater
 211          * than the nominal length of the prefix portion of the source
 212          * address. However the definition of the source prefix length is
 213          * not clear and thus this limiting is not yet implemented. */
 214         unsigned i;
 215         for (i=0; i<128 && !((s->s6_addr[i/8]^d->s6_addr[i/8])&(128>>(i%8))); i++);
 216         return i;
 217 }
 218
 219 #define DAS_USABLE              0x40000000
 220 #define DAS_MATCHINGSCOPE       0x20000000
 221 #define DAS_MATCHINGLABEL       0x10000000
 222 #define DAS_PREC_SHIFT          20
 223 #define DAS_SCOPE_SHIFT         16
 224 #define DAS_PREFIX_SHIFT        8
 225 #define DAS_ORDER_SHIFT         0
 226
 227 static int addrcmp(const void *_a, const void *_b)
 228 {
 229         const struct address *a = _a, *b = _b;
 230         return b->sortkey - a->sortkey;
 231 }
 232
 233 int __lookup_name(struct address buf[static MAXADDRS], char canon[static 256], const char *name, int family, int flags)
 234 {
 235         int cnt = 0, i, j;
 236
 237         *canon = 0;
 238         if (name) {
 239                 /* reject empty name and check len so it fits into temp bufs */
 240                 size_t l = strnlen(name, 255);
 241                 if (l-1 >= 254)
 242                         return EAI_NONAME;
 243                 memcpy(canon, name, l+1);
 244         }
 245
 246         /* Procedurally, a request for v6 addresses with the v4-mapped
 247          * flag set is like a request for unspecified family, followed
 248          * by filtering of the results. */
 249         if (flags & AI_V4MAPPED) {
 250                 if (family == AF_INET6) family = AF_UNSPEC;
 251                 else flags -= AI_V4MAPPED;
 252         }
 253
 254         /* Try each backend until there's at least one result. */
 255         cnt = name_from_null(buf, name, family, flags);
 256         if (!cnt) cnt = name_from_numeric(buf, name, family);
 257         if (!cnt && !(flags & AI_NUMERICHOST)) {
 258                 cnt = name_from_hosts(buf, canon, name, family);
 259                 if (!cnt) cnt = name_from_dns(buf, canon, name, family);
 260         }
 261         if (cnt<=0) return cnt ? cnt : EAI_NONAME;
 262
 263         /* Filter/transform results for v4-mapped lookup, if requested. */
 264         if (flags & AI_V4MAPPED) {
 265                 if (!(flags & AI_ALL)) {
 266                         /* If any v6 results exist, remove v4 results. */
 267                         for (i=0; i<cnt && buf[i].family != AF_INET6; i++);
 268                         if (i<cnt) {
 269                                 for (j=0; i<cnt; i++) {
 270                                         if (buf[i].family == AF_INET6)
 271                                                 buf[j++] = buf[i];
 272                                 }
 273                                 cnt = i = j;
 274                         }
 275                 }
 276                 /* Translate any remaining v4 results to v6 */
 277                 for (i=0; i<cnt; i++) {
 278                         if (buf[i].family != AF_INET) continue;
 279                         memcpy(buf[i].addr+12, buf[i].addr, 4);
 280                         memcpy(buf[i].addr, "\0\0\0\0\0\0\0\0\0\0\xff\xff", 12);
 281                         buf[i].family = AF_INET6;
 282                 }
 283         }
 284
 285         /* No further processing is needed if there are fewer than 2
 286          * results or if there are only IPv4 results. */
 287         if (cnt<2 || family==AF_INET) return cnt;
 288         for (i=0; buf[i].family == AF_INET; i++)
 289                 if (i==cnt) return cnt;
 290
 291         int cs;
 292         pthread_setcancelstate(PTHREAD_CANCEL_DISABLE, &cs);
 293
 294         /* The following implements a subset of RFC 3484/6724 destination
 295          * address selection by generating a single 31-bit sort key for
 296          * each address. Rules 3, 4, and 7 are omitted for having
 297          * excessive runtime and code size cost and dubious benefit.
 298          * So far the label/precedence table cannot be customized. */
 299         for (i=0; i<cnt; i++) {
 300                 int key = 0;
 301                 struct sockaddr_in6 sa, da = {
 302                         .sin6_family = AF_INET6,
 303                         .sin6_scope_id = buf[i].scopeid,
 304                         .sin6_port = 65535
 305                 };
 306                 if (buf[i].family == AF_INET6) {
 307                         memcpy(da.sin6_addr.s6_addr, buf[i].addr, 16);
 308                 } else {
 309                         memcpy(da.sin6_addr.s6_addr,
 310                                 "\0\0\0\0\0\0\0\0\0\0\xff\xff", 12);
 311                         memcpy(da.sin6_addr.s6_addr+12, buf[i].addr, 4);
 312                 }
 313                 const struct policy *dpolicy = policyof(&da.sin6_addr);
 314                 int dscope = scopeof(&da.sin6_addr);
 315                 int dlabel = dpolicy->label;
 316                 int dprec = dpolicy->prec;
 317                 int prefixlen = 0;
 318                 int fd = socket(AF_INET6, SOCK_DGRAM|SOCK_CLOEXEC, IPPROTO_UDP);
 319                 if (fd >= 0) {
 320                         if (!connect(fd, (void *)&da, sizeof da)) {
 321                                 key |= DAS_USABLE;
 322                                 if (!getsockname(fd, (void *)&sa,
 323                                     &(socklen_t){sizeof sa})) {
 324                                         if (dscope == scopeof(&sa.sin6_addr))
 325                                                 key |= DAS_MATCHINGSCOPE;
 326                                         if (dlabel == labelof(&sa.sin6_addr))
 327                                                 key |= DAS_MATCHINGLABEL;
 328                                         prefixlen = prefixmatch(&sa.sin6_addr,
 329                                                 &da.sin6_addr);
 330                                 }
 331                         }
 332                         close(fd);
 333                 }
 334                 key |= dprec << DAS_PREC_SHIFT;
 335                 key |= (15-dscope) << DAS_SCOPE_SHIFT;
 336                 key |= prefixlen << DAS_PREFIX_SHIFT;
 337                 key |= (MAXADDRS-i) << DAS_ORDER_SHIFT;
 338                 buf[i].sortkey = key;
 339         }
 340         qsort(buf, cnt, sizeof *buf, addrcmp);
 341
 342         pthread_setcancelstate(cs, 0);
 343
 344         return cnt;
 345 }