unix4lyfe git - darkstat/blob - dns.c

   1 /* darkstat 3
   2  * copyright (c) 2001-2008 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 "darkstat.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 "tree.h"
  18
  19 #include <sys/param.h>
  20 #include <sys/socket.h>
  21 #include <sys/wait.h>
  22 #include <assert.h>
  23 #include <errno.h>
  24 #include <netdb.h>
  25 #include <signal.h>
  26 #include <stdlib.h>
  27 #include <string.h>
  28 #include <unistd.h>
  29
  30 static void dns_main(void); /* this is what the child process runs */
  31
  32 #define CHILD 0 /* child process uses this socket */
  33 #define PARENT 1
  34 static int sock[2];
  35 static pid_t pid = -1;
  36
  37 struct dns_reply {
  38    struct addr46 addr;
  39    int error; /* for gai_strerror(), or 0 if no error */
  40    char name[MAXHOSTNAMELEN];
  41 };
  42
  43 void
  44 dns_init(const char *privdrop_user)
  45 {
  46    if (socketpair(AF_UNIX, SOCK_STREAM, 0, sock) == -1)
  47       err(1, "socketpair");
  48
  49    pid = fork();
  50    if (pid == -1)
  51       err(1, "fork");
  52
  53    if (pid == 0) {
  54       /* We are the child. */
  55       privdrop(NULL /* don't chroot */, privdrop_user);
  56       close(sock[PARENT]);
  57       sock[PARENT] = -1;
  58       daemonize_finish(); /* drop our copy of the lifeline! */
  59       if (signal(SIGUSR1, SIG_IGN) == SIG_ERR)
  60          errx(1, "signal(SIGUSR1, ignore) failed");
  61       dns_main();
  62       verbosef("fell out of dns_main()");
  63       exit(0);
  64    } else {
  65       /* We are the parent. */
  66       close(sock[CHILD]);
  67       sock[CHILD] = -1;
  68       fd_set_nonblock(sock[PARENT]);
  69       verbosef("DNS child has PID %d", pid);
  70    }
  71 }
  72
  73 void
  74 dns_stop(void)
  75 {
  76    if (pid == -1)
  77       return; /* no child was started */
  78    close(sock[PARENT]);
  79    if (kill(pid, SIGINT) == -1)
  80       err(1, "kill");
  81    verbosef("dns_stop() waiting for child");
  82    if (waitpid(pid, NULL, 0) == -1)
  83       err(1, "waitpid");
  84    verbosef("dns_stop() done waiting for child");
  85 }
  86
  87 struct tree_rec {
  88    RB_ENTRY(tree_rec) ptree;
  89    struct addr46 ip;
  90 };
  91
  92 static int
  93 tree_cmp(struct tree_rec *a, struct tree_rec *b)
  94 {
  95    if (a->ip.af != b->ip.af)
  96       /* Sort IPv4 to the left of IPv6.  */
  97       return (a->ip.af == AF_INET ? -1 : +1);
  98
  99    if (a->ip.af == AF_INET) {
 100       return (memcmp(&a->ip.addr.ip, &b->ip.addr.ip, sizeof(a->ip.addr.ip)));
 101    }
 102
 103    /* AF_INET6 should remain.  */
 104    if (a->ip.af == AF_INET6)
 105       return (memcmp(&a->ip.addr.ip6, &b->ip.addr.ip6, sizeof(a->ip.addr.ip6)));
 106
 107    /* Last resort.  */
 108    return -1;
 109 }
 110
 111 static RB_HEAD(tree_t, tree_rec) ip_tree = RB_INITIALIZER(&tree_rec);
 112 /* Quiet warnings. */
 113 static struct tree_rec * tree_t_RB_NEXT(struct tree_rec *elm)
 114    _unused_;
 115 static struct tree_rec * tree_t_RB_MINMAX(struct tree_t *head, int val)
 116    _unused_;
 117 RB_GENERATE(tree_t, tree_rec, ptree, tree_cmp)
 118
 119 void
 120 dns_queue(const struct addr46 *const ipaddr)
 121 {
 122    struct tree_rec *rec;
 123    ssize_t num_w;
 124
 125    if (pid == -1)
 126       return; /* no child was started - we're not doing any DNS */
 127
 128    if (ipaddr->af != AF_INET && ipaddr->af != AF_INET6) {
 129       verbosef("dns_queue() for unknown family %d.\n", ipaddr->af);
 130       return;
 131    }
 132
 133    rec = xmalloc(sizeof(*rec));
 134    memcpy(&rec->ip, ipaddr, sizeof(rec->ip));
 135
 136    if (RB_INSERT(tree_t, &ip_tree, rec) != NULL) {
 137       /* Already queued - this happens seldom enough that we don't care about
 138        * the performance hit of needlessly malloc()ing. */
 139       verbosef("already queued %s", ip_to_str(ipaddr));
 140       free(rec);
 141       return;
 142    }
 143
 144    num_w = write(sock[PARENT], ipaddr, sizeof(*ipaddr)); /* won't block */
 145    if (num_w == 0)
 146       warnx("dns_queue: write: ignoring end of file");
 147    else if (num_w == -1)
 148       warn("dns_queue: ignoring write error");
 149    else if (num_w != sizeof(*ipaddr))
 150       err(1, "dns_queue: wrote %z instead of %z", num_w, sizeof(*ipaddr));
 151 }
 152
 153 static void
 154 dns_unqueue(const struct addr46 *const ipaddr)
 155 {
 156    struct tree_rec tmp, *rec;
 157
 158    memcpy(&tmp.ip, ipaddr, sizeof(tmp.ip));
 159    if ((rec = RB_FIND(tree_t, &ip_tree, &tmp)) != NULL) {
 160       RB_REMOVE(tree_t, &ip_tree, rec);
 161       free(rec);
 162    }
 163    else
 164       verbosef("couldn't unqueue %s - not in queue!", ip_to_str(ipaddr));
 165 }
 166
 167 /*
 168  * Returns non-zero if result waiting, stores IP and name into given pointers
 169  * (name buffer is allocated by dns_poll)
 170  */
 171 static int
 172 dns_get_result(struct addr46 *ipaddr, char **name)
 173 {
 174    struct dns_reply reply;
 175    ssize_t numread;
 176
 177    numread = read(sock[PARENT], &reply, sizeof(reply));
 178    if (numread == -1) {
 179       if (errno == EAGAIN)
 180          return (0); /* no input waiting */
 181       else
 182          goto error;
 183    }
 184    if (numread == 0)
 185       goto error; /* EOF */
 186    if (numread != sizeof(reply))
 187       errx(1, "dns_get_result read got %z, expected %z", numread, sizeof(reply));
 188
 189    /* Return successful reply. */
 190    memcpy(ipaddr, &reply.addr, sizeof(*ipaddr));
 191 #if DARKSTAT_USES_HOSTENT
 192    if (reply.error != 0)
 193       xasprintf(name, "(%s)", hstrerror(reply.error));
 194    else
 195       *name = xstrdup(reply.name);
 196 #else /* !DARKSTAT_USES_HOSTENT */
 197    if (reply.error != 0) {
 198       /* Identify common special cases.  */
 199       char *type = "none";
 200
 201       if (reply.addr.af == AF_INET6) {
 202          if (IN6_IS_ADDR_LINKLOCAL(&reply.addr.addr.ip6))
 203             type = "link-local";
 204          else if (IN6_IS_ADDR_SITELOCAL(&reply.addr.addr.ip6))
 205             type = "site-local";
 206          else if (IN6_IS_ADDR_MULTICAST(&reply.addr.addr.ip6))
 207             type = "multicast";
 208       } else { /* AF_INET */
 209          if (IN_MULTICAST(reply.addr.addr.ip.s_addr))
 210             type = "multicast";
 211       }
 212       xasprintf(name, "(%s)", type);
 213    }
 214    else  /* Correctly resolved name.  */
 215       *name = xstrdup(reply.name);
 216 #endif /* !DARKSTAT_USES_HOSTENT */
 217
 218    dns_unqueue(&reply.addr);
 219    return (1);
 220
 221 error:
 222    warn("dns_get_result: ignoring read error");
 223    /* FIXME: re-align to stream?  restart dns child? */
 224    return (0);
 225 }
 226
 227 void
 228 dns_poll(void)
 229 {
 230    struct addr46 ip;
 231    char *name;
 232
 233    if (pid == -1)
 234       return; /* no child was started - we're not doing any DNS */
 235
 236    while (dns_get_result(&ip, &name)) {
 237       /* push into hosts_db */
 238       struct bucket *b = host_find(&ip);
 239
 240       if (b == NULL) {
 241          verbosef("resolved %s to %s but it's not in the DB!",
 242             ip_to_str(&ip), name);
 243          return;
 244       }
 245       if (b->u.host.dns != NULL) {
 246          verbosef("resolved %s to %s but it's already in the DB!",
 247             ip_to_str(&ip), name);
 248          return;
 249       }
 250       b->u.host.dns = name;
 251    }
 252 }
 253
 254 /* ------------------------------------------------------------------------ */
 255
 256 struct qitem {
 257    STAILQ_ENTRY(qitem) entries;
 258    struct addr46 ip;
 259 };
 260
 261 STAILQ_HEAD(qhead, qitem) queue = STAILQ_HEAD_INITIALIZER(queue);
 262
 263 static void
 264 enqueue(const struct addr46 *const ip)
 265 {
 266    struct qitem *i;
 267
 268    i = xmalloc(sizeof(*i));
 269    memcpy(&i->ip, ip, sizeof(i->ip));
 270    STAILQ_INSERT_TAIL(&queue, i, entries);
 271    verbosef("DNS: enqueued %s", ip_to_str(ip));
 272 }
 273
 274 /* Return non-zero and populate <ip> pointer if queue isn't empty. */
 275 static int
 276 dequeue(struct addr46 *ip)
 277 {
 278    struct qitem *i;
 279
 280    i = STAILQ_FIRST(&queue);
 281    if (i == NULL)
 282       return (0);
 283    STAILQ_REMOVE_HEAD(&queue, entries);
 284    memcpy(ip, &i->ip, sizeof(*ip));
 285    free(i);
 286    verbosef("DNS: dequeued %s", ip_to_str(ip));
 287    return 1;
 288 }
 289
 290 static void
 291 xwrite(const int d, const void *buf, const size_t nbytes)
 292 {
 293    ssize_t ret = write(d, buf, nbytes);
 294
 295    if (ret == -1)
 296       err(1, "write");
 297    if (ret != (ssize_t)nbytes)
 298       err(1, "wrote %d bytes instead of all %d bytes", (int)ret, (int)nbytes);
 299 }
 300
 301 static void
 302 dns_main(void)
 303 {
 304    struct addr46 ip;
 305
 306 #ifdef HAVE_SETPROCTITLE
 307    setproctitle("DNS child");
 308 #endif
 309    fd_set_nonblock(sock[CHILD]);
 310    verbosef("DNS child entering main DNS loop");
 311    for (;;) {
 312       int blocking;
 313
 314       if (STAILQ_EMPTY(&queue)) {
 315          blocking = 1;
 316          fd_set_block(sock[CHILD]);
 317          verbosef("entering blocking read loop");
 318       } else {
 319          blocking = 0;
 320          fd_set_nonblock(sock[CHILD]);
 321          verbosef("non-blocking poll");
 322       }
 323       for (;;) {
 324          /* While we have input to process... */
 325          ssize_t numread = read(sock[CHILD], &ip, sizeof(ip));
 326          if (numread == 0)
 327             exit(0); /* end of file, nothing more to do here. */
 328          if (numread == -1) {
 329             if (!blocking && (errno == EAGAIN))
 330                break; /* ran out of input */
 331             /* else error */
 332             err(1, "DNS: read failed");
 333          }
 334          if (numread != sizeof(ip))
 335             err(1, "DNS: read got %z bytes, expecting %z", numread, sizeof(ip));
 336          enqueue(&ip);
 337          if (blocking) {
 338             /* After one blocking read, become non-blocking so that when we
 339              * run out of input we fall through to queue processing.
 340              */
 341             blocking = 0;
 342             fd_set_nonblock(sock[CHILD]);
 343          }
 344       }
 345
 346       /* Process queue. */
 347       if (dequeue(&ip)) {
 348          struct dns_reply reply;
 349 #if DARKSTAT_USES_HOSTENT
 350          struct hostent *he;
 351
 352          memcpy(&reply.addr, &ip, sizeof(reply.addr));
 353          he = gethostbyaddr((char *)&ip.addr.ip, sizeof(ip.addr.ip), ip.af); /* TODO MEA */
 354
 355          /* On some platforms (for example Linux with GLIBC 2.3.3), h_errno
 356           * will be non-zero here even though the lookup succeeded.
 357           */
 358          if (he == NULL) {
 359             reply.name[0] = '\0';
 360             reply.error = h_errno;
 361          } else {
 362             assert(sizeof(reply.name) > sizeof(char *)); /* not just a ptr */
 363             strlcpy(reply.name, he->h_name, sizeof(reply.name));
 364             reply.error = 0;
 365          }
 366          fd_set_block(sock[CHILD]);
 367          xwrite(sock[CHILD], &reply, sizeof(reply));
 368          verbosef("DNS: %s is %s", ip_to_str(&reply.addr),
 369             (h_errno == 0)?reply.name:hstrerror(h_errno));
 370 #else /* !DARKSTAT_USES_HOSTENT */
 371          struct sockaddr_in sin;
 372          struct sockaddr_in6 sin6;
 373          char host[NI_MAXHOST];
 374          int ret, flags;
 375
 376          reply.addr.af = ip.af;
 377          flags = NI_NAMEREQD;
 378 #  ifdef NI_IDN
 379          flags |= NI_IDN;
 380 #  endif
 381          switch (ip.af) {
 382             case AF_INET:
 383                sin.sin_family = ip.af;
 384                memcpy(&reply.addr.addr.ip, &ip.addr.ip, sizeof(reply.addr.addr.ip));
 385                memcpy(&sin.sin_addr, &ip.addr.ip, sizeof(sin.sin_addr));
 386                ret = getnameinfo((struct sockaddr *) &sin, sizeof(sin),
 387                                  host, sizeof(host), NULL, 0, flags);
 388                break;
 389             case AF_INET6:
 390                sin6.sin6_family = ip.af;
 391                memcpy(&reply.addr.addr.ip6, &ip.addr.ip6, sizeof(reply.addr.addr.ip6));
 392                memcpy(&sin6.sin6_addr, &ip.addr.ip6, sizeof(sin6.sin6_addr));
 393                ret = getnameinfo((struct sockaddr *) &sin6, sizeof(sin6),
 394                                  host, sizeof(host), NULL, 0, flags);
 395                break;
 396             default:
 397                ret = EAI_FAMILY;
 398
 399          }
 400
 401          if (ret != 0) {
 402             reply.name[0] = '\0';
 403             reply.error = ret;
 404          } else {
 405             assert(sizeof(reply.name) > sizeof(char *)); /* not just a ptr */
 406             strlcpy(reply.name, host, sizeof(reply.name));
 407             reply.error = 0;
 408          }
 409          fd_set_block(sock[CHILD]);
 410          xwrite(sock[CHILD], &reply, sizeof(reply));
 411          verbosef("DNS: %s is \"%s\".", ip_to_str(&reply.addr),
 412             (ret == 0) ? reply.name : gai_strerror(ret));
 413 #endif /* !DARKSTAT_USES_HOSTENT */
 414       }
 415    }
 416 }
 417
 418 /* vim:set ts=3 sw=3 tw=78 expandtab: */