unix4lyfe git - darkstat-debian/blob - dns.c

   1 /* darkstat 3
   2  * copyright (c) 2001-2014 Emil Mikulic.
   3  *
   4  * dns.c: synchronous DNS in a child process.
   5  *
   6  * You may use, modify and redistribute this file under the terms of the
   7  * GNU General Public License version 2. (see COPYING.GPL)
   8  */
   9
  10 #include "cdefs.h"
  11 #include "conv.h"
  12 #include "decode.h"
  13 #include "dns.h"
  14 #include "err.h"
  15 #include "hosts_db.h"
  16 #include "queue.h"
  17 #include "str.h"
  18 #include "tree.h"
  19 #include "bsd.h" /* for setproctitle, strlcpy */
  20
  21 #include <sys/param.h>
  22 #include <sys/socket.h>
  23 #include <sys/wait.h>
  24 #include <assert.h>
  25 #include <errno.h>
  26 #include <netdb.h>
  27 #include <signal.h>
  28 #include <stdlib.h>
  29 #include <string.h>
  30 #include <unistd.h>
  31
  32 #ifdef __NetBSD__
  33 # define gethostbyaddr(addr, len, type) \
  34          gethostbyaddr((const char *)(addr), len, type)
  35 #endif
  36
  37 static void dns_main(void) _noreturn_; /* the child process runs this */
  38
  39 #define CHILD 0 /* child process uses this socket */
  40 #define PARENT 1
  41 static int dns_sock[2];
  42 static pid_t pid = -1;
  43
  44 struct dns_reply {
  45    struct addr addr;
  46    int error; /* for gai_strerror(), or 0 if no error */
  47    char name[256]; /* http://tools.ietf.org/html/rfc1034#section-3.1 */
  48 };
  49
  50 void
  51 dns_init(const char *privdrop_user)
  52 {
  53    if (socketpair(AF_UNIX, SOCK_STREAM, 0, dns_sock) == -1)
  54       err(1, "socketpair");
  55
  56    pid = fork();
  57    if (pid == -1)
  58       err(1, "fork");
  59
  60    if (pid == 0) {
  61       /* We are the child. */
  62       privdrop(NULL /* don't chroot */, privdrop_user);
  63       close(dns_sock[PARENT]);
  64       dns_sock[PARENT] = -1;
  65       daemonize_finish(); /* drop our copy of the lifeline! */
  66       if (signal(SIGUSR1, SIG_IGN) == SIG_ERR)
  67          errx(1, "signal(SIGUSR1, ignore) failed");
  68       dns_main();
  69       exit(0);
  70    } else {
  71       /* We are the parent. */
  72       close(dns_sock[CHILD]);
  73       dns_sock[CHILD] = -1;
  74       fd_set_nonblock(dns_sock[PARENT]);
  75       verbosef("DNS child has PID %d", pid);
  76    }
  77 }
  78
  79 void
  80 dns_stop(void)
  81 {
  82    if (pid == -1)
  83       return; /* no child was started */
  84    close(dns_sock[PARENT]);
  85    if (kill(pid, SIGINT) == -1)
  86       err(1, "kill");
  87    verbosef("dns_stop() waiting for child");
  88    if (waitpid(pid, NULL, 0) == -1)
  89       err(1, "waitpid");
  90    verbosef("dns_stop() done waiting for child");
  91 }
  92
  93 struct tree_rec {
  94    RB_ENTRY(tree_rec) ptree;
  95    struct addr ip;
  96 };
  97
  98 static int
  99 tree_cmp(struct tree_rec *a, struct tree_rec *b)
 100 {
 101    if (a->ip.family != b->ip.family)
 102       /* Sort IPv4 to the left of IPv6.  */
 103       return ((a->ip.family == IPv4) ? -1 : +1);
 104
 105    if (a->ip.family == IPv4)
 106       return (memcmp(&a->ip.ip.v4, &b->ip.ip.v4, sizeof(a->ip.ip.v4)));
 107    else {
 108       assert(a->ip.family == IPv6);
 109       return (memcmp(&a->ip.ip.v6, &b->ip.ip.v6, sizeof(a->ip.ip.v6)));
 110    }
 111 }
 112
 113 static RB_HEAD(tree_t, tree_rec) ip_tree = RB_INITIALIZER(&tree_rec);
 114 RB_GENERATE_STATIC(tree_t, tree_rec, ptree, tree_cmp)
 115
 116 void
 117 dns_queue(const struct addr *const ipaddr)
 118 {
 119    struct tree_rec *rec;
 120    ssize_t num_w;
 121
 122    if (pid == -1)
 123       return; /* no child was started - we're not doing any DNS */
 124
 125    if ((ipaddr->family != IPv4) && (ipaddr->family != IPv6)) {
 126       verbosef("dns_queue() for unknown family %d", ipaddr->family);
 127       return;
 128    }
 129
 130    rec = xmalloc(sizeof(*rec));
 131    memcpy(&rec->ip, ipaddr, sizeof(rec->ip));
 132
 133    if (RB_INSERT(tree_t, &ip_tree, rec) != NULL) {
 134       /* Already queued - this happens seldom enough that we don't care about
 135        * the performance hit of needlessly malloc()ing. */
 136       verbosef("already queued %s", addr_to_str(ipaddr));
 137       free(rec);
 138       return;
 139    }
 140
 141    num_w = write(dns_sock[PARENT], ipaddr, sizeof(*ipaddr)); /* won't block */
 142    if (num_w == 0)
 143       warnx("dns_queue: write: ignoring end of file");
 144    else if (num_w == -1)
 145       warn("dns_queue: ignoring write error");
 146    else if (num_w != sizeof(*ipaddr))
 147       err(1, "dns_queue: wrote %zu instead of %zu", num_w, sizeof(*ipaddr));
 148 }
 149
 150 static void
 151 dns_unqueue(const struct addr *const ipaddr)
 152 {
 153    struct tree_rec tmp, *rec;
 154
 155    memcpy(&tmp.ip, ipaddr, sizeof(tmp.ip));
 156    if ((rec = RB_FIND(tree_t, &ip_tree, &tmp)) != NULL) {
 157       RB_REMOVE(tree_t, &ip_tree, rec);
 158       free(rec);
 159    }
 160    else
 161       verbosef("couldn't unqueue %s - not in queue!", addr_to_str(ipaddr));
 162 }
 163
 164 /*
 165  * Returns non-zero if result waiting, stores IP and name into given pointers
 166  * (name buffer is allocated by dns_poll)
 167  */
 168 static int
 169 dns_get_result(struct addr *ipaddr, char **name)
 170 {
 171    struct dns_reply reply;
 172    ssize_t numread;
 173
 174    numread = read(dns_sock[PARENT], &reply, sizeof(reply));
 175    if (numread == -1) {
 176       if (errno == EAGAIN)
 177          return (0); /* no input waiting */
 178       else
 179          goto error;
 180    }
 181    if (numread == 0)
 182       goto error; /* EOF */
 183    if (numread != sizeof(reply))
 184       errx(1, "dns_get_result read got %zu, expected %zu",
 185          numread, sizeof(reply));
 186
 187    /* Return successful reply. */
 188    memcpy(ipaddr, &reply.addr, sizeof(*ipaddr));
 189    if (reply.error != 0) {
 190       /* Identify common special cases.  */
 191       const char *type = "none";
 192
 193       if (reply.addr.family == IPv6) {
 194          if (IN6_IS_ADDR_LINKLOCAL(&reply.addr.ip.v6))
 195             type = "link-local";
 196          else if (IN6_IS_ADDR_SITELOCAL(&reply.addr.ip.v6))
 197             type = "site-local";
 198          else if (IN6_IS_ADDR_MULTICAST(&reply.addr.ip.v6))
 199             type = "multicast";
 200       } else {
 201          assert(reply.addr.family == IPv4);
 202          if (IN_MULTICAST(htonl(reply.addr.ip.v4)))
 203             type = "multicast";
 204       }
 205       xasprintf(name, "(%s)", type);
 206    }
 207    else  /* Correctly resolved name.  */
 208       *name = xstrdup(reply.name);
 209
 210    dns_unqueue(&reply.addr);
 211    return (1);
 212
 213 error:
 214    warn("dns_get_result: ignoring read error");
 215    /* FIXME: re-align to stream?  restart dns child? */
 216    return (0);
 217 }
 218
 219 void
 220 dns_poll(void)
 221 {
 222    struct addr ip;
 223    char *name;
 224
 225    if (pid == -1)
 226       return; /* no child was started - we're not doing any DNS */
 227
 228    while (dns_get_result(&ip, &name)) {
 229       /* push into hosts_db */
 230       struct bucket *b = host_find(&ip);
 231
 232       if (b == NULL) {
 233          verbosef("resolved %s to %s but it's not in the DB!",
 234             addr_to_str(&ip), name);
 235          return;
 236       }
 237       if (b->u.host.dns != NULL) {
 238          verbosef("resolved %s to %s but it's already in the DB!",
 239             addr_to_str(&ip), name);
 240          return;
 241       }
 242       b->u.host.dns = name;
 243    }
 244 }
 245
 246 /* ------------------------------------------------------------------------ */
 247
 248 struct qitem {
 249    STAILQ_ENTRY(qitem) entries;
 250    struct addr ip;
 251 };
 252
 253 static STAILQ_HEAD(qhead, qitem) queue = STAILQ_HEAD_INITIALIZER(queue);
 254
 255 static void
 256 enqueue(const struct addr *const ip)
 257 {
 258    struct qitem *i;
 259
 260    i = xmalloc(sizeof(*i));
 261    memcpy(&i->ip, ip, sizeof(i->ip));
 262    STAILQ_INSERT_TAIL(&queue, i, entries);
 263    verbosef("DNS: enqueued %s", addr_to_str(ip));
 264 }
 265
 266 /* Return non-zero and populate <ip> pointer if queue isn't empty. */
 267 static int
 268 dequeue(struct addr *ip)
 269 {
 270    struct qitem *i;
 271
 272    i = STAILQ_FIRST(&queue);
 273    if (i == NULL)
 274       return (0);
 275    STAILQ_REMOVE_HEAD(&queue, entries);
 276    memcpy(ip, &i->ip, sizeof(*ip));
 277    free(i);
 278    verbosef("DNS: dequeued %s", addr_to_str(ip));
 279    return 1;
 280 }
 281
 282 static void
 283 xwrite(const int d, const void *buf, const size_t nbytes)
 284 {
 285    ssize_t ret = write(d, buf, nbytes);
 286
 287    if (ret == -1)
 288       err(1, "write");
 289    if (ret != (ssize_t)nbytes)
 290       err(1, "wrote %d bytes instead of all %d bytes", (int)ret, (int)nbytes);
 291 }
 292
 293 static void
 294 dns_main(void)
 295 {
 296    struct addr ip;
 297
 298    setproctitle("DNS child");
 299    fd_set_nonblock(dns_sock[CHILD]);
 300    verbosef("DNS child entering main DNS loop");
 301    for (;;) {
 302       int blocking;
 303
 304       if (STAILQ_EMPTY(&queue)) {
 305          blocking = 1;
 306          fd_set_block(dns_sock[CHILD]);
 307          verbosef("entering blocking read loop");
 308       } else {
 309          blocking = 0;
 310          fd_set_nonblock(dns_sock[CHILD]);
 311          verbosef("non-blocking poll");
 312       }
 313       for (;;) {
 314          /* While we have input to process... */
 315          ssize_t numread = read(dns_sock[CHILD], &ip, sizeof(ip));
 316          if (numread == 0)
 317             exit(0); /* end of file, nothing more to do here. */
 318          if (numread == -1) {
 319             if (!blocking && (errno == EAGAIN))
 320                break; /* ran out of input */
 321             /* else error */
 322             err(1, "DNS: read failed");
 323          }
 324          if (numread != sizeof(ip))
 325             err(1, "DNS: read got %zu bytes, expecting %zu",
 326                numread, sizeof(ip));
 327          enqueue(&ip);
 328          if (blocking) {
 329             /* After one blocking read, become non-blocking so that when we
 330              * run out of input we fall through to queue processing.
 331              */
 332             blocking = 0;
 333             fd_set_nonblock(dns_sock[CHILD]);
 334          }
 335       }
 336
 337       /* Process queue. */
 338       if (dequeue(&ip)) {
 339          struct dns_reply reply;
 340          struct sockaddr_in sin;
 341          struct sockaddr_in6 sin6;
 342          struct hostent *he;
 343          char host[NI_MAXHOST];
 344          int ret, flags;
 345
 346          reply.addr = ip;
 347          flags = NI_NAMEREQD;
 348 #  ifdef NI_IDN
 349          flags |= NI_IDN;
 350 #  endif
 351          switch (ip.family) {
 352             case IPv4:
 353                sin.sin_family = AF_INET;
 354                sin.sin_addr.s_addr = ip.ip.v4;
 355                ret = getnameinfo((struct sockaddr *) &sin, sizeof(sin),
 356                                  host, sizeof(host), NULL, 0, flags);
 357                if (ret == EAI_FAMILY) {
 358                   verbosef("getnameinfo error %s, trying gethostbyname",
 359                      gai_strerror(ret));
 360                   he = gethostbyaddr(&sin.sin_addr.s_addr,
 361                      sizeof(sin.sin_addr.s_addr), sin.sin_family);
 362                   if (he == NULL) {
 363                      ret = EAI_FAIL;
 364                      verbosef("gethostbyname error %s", hstrerror(h_errno));
 365                   } else {
 366                      ret = 0;
 367                      strlcpy(host, he->h_name, sizeof(host));
 368                   }
 369                }
 370                break;
 371             case IPv6:
 372                sin6.sin6_family = AF_INET6;
 373                memcpy(&sin6.sin6_addr, &ip.ip.v6, sizeof(sin6.sin6_addr));
 374                ret = getnameinfo((struct sockaddr *) &sin6, sizeof(sin6),
 375                                  host, sizeof(host), NULL, 0, flags);
 376                break;
 377             default:
 378                ret = EAI_FAMILY;
 379          }
 380
 381          if (ret != 0) {
 382             reply.name[0] = '\0';
 383             reply.error = ret;
 384          } else {
 385             assert(sizeof(reply.name) > sizeof(char *)); /* not just a ptr */
 386             strlcpy(reply.name, host, sizeof(reply.name));
 387             reply.error = 0;
 388          }
 389          fd_set_block(dns_sock[CHILD]);
 390          xwrite(dns_sock[CHILD], &reply, sizeof(reply));
 391          verbosef("DNS: %s is \"%s\".", addr_to_str(&reply.addr),
 392             (ret == 0) ? reply.name : gai_strerror(ret));
 393       }
 394    }
 395 }
 396
 397 /* vim:set ts=3 sw=3 tw=78 expandtab: */