resolver.c 13.7 KB
1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60 61 62 63 64 65 66 67 68 69 70 71 72 73 74 75 76 77 78 79 80 81 82 83 84 85 86 87 88 89 90 91 92 93 94 95 96 97 98 99 100 101 102 103 104 105 106 107 108 109 110 111 112 113 114 115 116 117 118 119 120 121 122 123 124 125 126 127 128 129 130 131 132 133 134 135 136 137 138 139 140 141 142 143 144 145 146 147 148 149 150 151 152 153 154 155 156 157 158 159 160 161 162 163 164 165 166 167 168 169 170 171 172 173 174 175 176 177 178 179 180 181 182 183 184 185 186 187 188 189 190 191 192 193 194 195 196 197 198 199 200 201 202 203 204 205 206 207 208 209 210 211 212 213 214 215 216 217 218 219 220 221 222 223 224 225 226 227 228 229 230 231 232 233 234 235 236 237 238 239 240 241 242 243 244 245 246 247 248 249 250 251 252 253 254 255 256 257 258 259 260 261 262 263 264 265 266 267 268 269 270 271 272 273 274 275 276 277 278 279 280 281 282 283 284 285 286 287 288 289 290 291 292 293 294 295 296 297 298 299 300 301 302 303 304 305 306 307 308 309 310 311 312 313 314 315 316 317 318 319 320 321 322 323 324 325 326 327 328 329 330 331 332 333 334 335 336 337 338 339 340 341 342 343 344 345 346 347 348 349 350 351 352 353 354 355 356 357 358 359 360 361 362 363 364 365 366 367 368 369 370 371 372 373 374 375 376 377 378 379 380 381 382 383 384 385 386 387 388 389 390 391 392 393 394 395 396 397 398 399 400 401 402 403 404 405 406 407 408 409 410 411 412 413 414 415 416 417 418 419 420 421 422 423 424 425 426 427 428 429 430 431 432 433 434 435 436 437 438 439 440 441 442 443 444 445 446 447 448 449 450 451 452 453 454 455 456 457 458 459 460 461 462 463 464 465 466 467 468 469 470 471 472 473 474 475 476 477 478 479 480 481 482 483 484 485 486 487 488 489 490 491 492 493 494 495 496 497 498 499 500 501 502 503 504 505 506 507 508 509 510 511 512 513 514 515 516 517 518 519 520 521 522 523 524 525 526 527
/*
 * resolver.c:
 *
 */

#include <sys/types.h>
#include <sys/socket.h>
#include <netinet/in.h>
#include <arpa/inet.h>
#include <pthread.h>
#include <stdio.h>
#include <stdlib.h>
#include <netdb.h>
#include <errno.h>
#include <string.h>
#include <unistd.h>

#include "ns_hash.h"
#include "iftop.h"

#include "threadprof.h"

#include "options.h"


#define RESOLVE_QUEUE_LENGTH 20

struct addr_storage {
    int af;                     /* AF_INET or AF_INET6 */
    int len;                    /* sizeof(struct in_addr or in6_addr) */
    union {
        struct in_addr  addr4;
        struct in6_addr addr6;
    } addr;
#define as_addr4 addr.addr4
#define as_addr6 addr.addr6
};

struct addr_storage resolve_queue[RESOLVE_QUEUE_LENGTH];

pthread_cond_t resolver_queue_cond;
pthread_mutex_t resolver_queue_mutex;

hash_type* ns_hash;

int head;
int tail;

extern options_t options;


/* 
 * We have a choice of resolver methods. Real computers have getnameinfo or
 * gethostbyaddr_r, which are reentrant and therefore thread safe. Other
 * machines don't, and so we can use non-reentrant gethostbyaddr and have only
 * one resolver thread.  Alternatively, we can use the MIT ares asynchronous
 * DNS library to do this.
 */

#if defined(USE_GETNAMEINFO)
/**
 * Implementation of do_resolve for platforms with getaddrinfo.
 *
 * This is a fairly sane function with a uniform interface which is even --
 * shock! -- standardised by POSIX and in RFC 2553. Unfortunately systems such
 * as NetBSD break the RFC and implement it in a non-thread-safe fashion, so
 * for the moment, the configure script won't try to use it.
 */
char *do_resolve(struct addr_storage *addr) {
    struct sockaddr_in sin;
    struct sockaddr_in6 sin6;
    char buf[NI_MAXHOST]; /* 1025 */
    int ret;

    switch (addr->af) {
        case AF_INET:
            sin.sin_family = addr->af;
            sin.sin_port = 0;
            memcpy(&sin.sin_addr, &addr->as_addr4, addr->len);

            ret = getnameinfo((struct sockaddr*)&sin, sizeof sin,
                              buf, sizeof buf, NULL, 0, NI_NAMEREQD);
            break;
        case AF_INET6:
            sin6.sin6_family = addr->af;
            sin6.sin6_port = 0;
            memcpy(&sin6.sin6_addr, &addr->as_addr6, addr->len);

            ret = getnameinfo((struct sockaddr*)&sin6, sizeof sin6,
                              buf, sizeof buf, NULL, 0, NI_NAMEREQD);
	    break;
        default:
            return NULL;
    }

    if (ret == 0)
        return xstrdup(buf);
    else
        return NULL;
}

#elif defined(USE_GETHOSTBYADDR_R)
/**
 * Implementation of do_resolve for platforms with working gethostbyaddr_r
 *
 * Some implementations of libc choose to implement gethostbyaddr_r as
 * a non thread-safe wrapper to gethostbyaddr.  An interesting choice...
 */
char* do_resolve(struct addr_storage *addr) {
    struct hostent hostbuf, *hp = NULL;
    size_t hstbuflen = 1024;
    char *tmphstbuf;
    int res = 0;
    int herr;
    char * ret = NULL;

    /* Allocate buffer, remember to free it to avoid memory leakage. */
    tmphstbuf = xmalloc (hstbuflen);

    /* nss-myhostname's gethostbyaddr_r() causes an assertion failure if an
     * "invalid" (as in outside of IPv4 or IPv6) address family is passed */
    if (addr->af == AF_INET || addr->af == AF_INET6) {

    /* Some machines have gethostbyaddr_r returning an integer error code; on
     * others, it returns a struct hostent*. */
#ifdef GETHOSTBYADDR_R_RETURNS_INT
    while ((res = gethostbyaddr_r((char*)&addr->addr, addr->len, addr->af,
                                  &hostbuf, tmphstbuf, hstbuflen,
                                  &hp, &herr)) == ERANGE)
#else
    /* ... also assume one fewer argument.... */
    while ((hp = gethostbyaddr_r((char*)&addr->addr, addr->len, addr->af,
                                 &hostbuf, tmphstbuf, hstbuflen, &herr)) == NULL
            && errno == ERANGE)
#endif
            {
        
        /* Enlarge the buffer.  */
        hstbuflen *= 2;
        tmphstbuf = realloc (tmphstbuf, hstbuflen);
      }
    }

    /*  Check for errors.  */
    if (res || hp == NULL) {
        /* failed */
        /* Leave the unresolved IP in the hash */
    }
    else {
        ret = xstrdup(hp->h_name);

    }
    xfree(tmphstbuf);
    return ret;
}

#elif defined(USE_GETHOSTBYADDR)

/**
 * Implementation using gethostbyname. Since this is nonreentrant, we have to
 * wrap it in a mutex, losing all benefit of multithreaded resolution.
 */
char *do_resolve(struct addr_storage *addr) {
    static pthread_mutex_t ghba_mtx = PTHREAD_MUTEX_INITIALIZER;
    char *s = NULL;
    struct hostent *he;
    pthread_mutex_lock(&ghba_mtx);
    he = gethostbyaddr((char*)&addr->addr, addr->len, addr->af);
    if (he)
        s = xstrdup(he->h_name);
    pthread_mutex_unlock(&ghba_mtx);
    return s;
}


#elif defined(USE_LIBRESOLV)

#include <arpa/nameser.h>
#include <resolv.h>

/**
 * libresolv implementation 
 * resolver functions may not be thread safe
 */
char* do_resolve(struct addr_storage *addr) {
  char msg[PACKETSZ];
  char s[35];
  int l;
  unsigned char* a;
  char * ret = NULL;

  if (addr->af != AF_INET)
    return NULL;

  a = (unsigned char*)&addr->addr;

  snprintf(s, 35, "%d.%d.%d.%d.in-addr.arpa.",a[3], a[2], a[1], a[0]);

  l = res_search(s, C_IN, T_PTR, msg, PACKETSZ);
  if(l != -1) {
    ns_msg nsmsg;
    ns_rr rr;
    if(ns_initparse(msg, l, &nsmsg) != -1) {
      int c;
      int i;
      c = ns_msg_count(nsmsg, ns_s_an);
      for(i = 0; i < c; i++) {
        if(ns_parserr(&nsmsg, ns_s_an, i, &rr) == 0){
          if(ns_rr_type(rr) == T_PTR) {
            char buf[256];
            ns_name_uncompress(msg, msg + l, ns_rr_rdata(rr), buf, 256);
            ret = xstrdup(buf);
          }
        }
      }
    }
  }
  return ret;
}

#elif defined(USE_ARES)

/**
 * ares implementation
 */

#include <sys/time.h>
#include <ares.h>
#include <arpa/nameser.h>

/* callback function for ares */
struct ares_callback_comm {
    struct in_addr *addr;
    int result;
    char *name;
};

static void do_resolve_ares_callback(void *arg, int status, unsigned char *abuf, int alen) {
    struct hostent *he;
    struct ares_callback_comm *C;
    C = (struct ares_callback_comm*)arg;

    if (status == ARES_SUCCESS) {
        C->result = 1;
        ares_parse_ptr_reply(abuf, alen, C->addr, sizeof *C->addr, AF_INET, &he);
        C->name = xstrdup(he->h_name);;
        ares_free_hostent(he);
    } else {
        C->result = -1;
    }
}

char *do_resolve(struct addr_storage * addr) {
    struct ares_callback_comm C;
    char s[35];
    unsigned char *a;
    ares_channel *chan;
    static pthread_mutex_t ares_init_mtx = PTHREAD_MUTEX_INITIALIZER;
    static pthread_key_t ares_key;
    static int gotkey;

    if (addr->af != AF_INET)
        return NULL;

    /* Make sure we have an ARES channel for this thread. */
    pthread_mutex_lock(&ares_init_mtx);
    if (!gotkey) {
        pthread_key_create(&ares_key, NULL);
        gotkey = 1;
        
    }
    pthread_mutex_unlock(&ares_init_mtx);
    
    chan = pthread_getspecific(ares_key);
    if (!chan) {
        chan = xmalloc(sizeof *chan);
        pthread_setspecific(ares_key, chan);
        if (ares_init(chan) != ARES_SUCCESS) return NULL;
    }
    
    a = (unsigned char*)&addr->as_addr4;
    sprintf(s, "%d.%d.%d.%d.in-addr.arpa.", a[3], a[2], a[1], a[0]);
    
    C.result = 0;
    C.addr = &addr->as_addr4;
    ares_query(*chan, s, C_IN, T_PTR, do_resolve_ares_callback, &C);
    while (C.result == 0) {
        int n;
        fd_set readfds, writefds;
        struct timeval tv;
        FD_ZERO(&readfds);
        FD_ZERO(&writefds);
        n = ares_fds(*chan, &readfds, &writefds);
        ares_timeout(*chan, NULL, &tv);
        select(n, &readfds, &writefds, NULL, &tv);
        ares_process(*chan, &readfds, &writefds);
    }

    /* At this stage, the query should be complete. */
    switch (C.result) {
        case -1:
        case 0:     /* shouldn't happen */
            return NULL;

        default:
            return C.name;
    }
}

#elif defined(USE_FORKING_RESOLVER)

/**
 * Resolver which forks a process, then uses gethostbyname.
 */

#include <signal.h>

#define NAMESIZE        64

int forking_resolver_worker(int fd) {
    while (1) {
        struct addr_storage a;
        struct hostent *he;
        char buf[NAMESIZE] = {0};
        if (read(fd, &a, sizeof a) != sizeof a)
            return -1;

        he = gethostbyaddr((char*)&a.addr, a.len, a.af);
        if (he)
            strncpy(buf, he->h_name, NAMESIZE - 1);

        if (write(fd, buf, NAMESIZE) != NAMESIZE)
            return -1;
    }
}

char *do_resolve(struct in6_addr *addr) {
    struct {
        int fd;
        pid_t child;
    } *workerinfo;
    char name[NAMESIZE];
    static pthread_mutex_t worker_init_mtx = PTHREAD_MUTEX_INITIALIZER;
    static pthread_key_t worker_key;
    static int gotkey;

    /* If no process exists, we need to spawn one. */
    pthread_mutex_lock(&worker_init_mtx);
    if (!gotkey) {
        pthread_key_create(&worker_key, NULL);
        gotkey = 1;
    }
    pthread_mutex_unlock(&worker_init_mtx);
    
    workerinfo = pthread_getspecific(worker_key);
    if (!workerinfo) {
        int p[2];

        if (socketpair(AF_UNIX, SOCK_STREAM, PF_UNSPEC, p) == -1)
            return NULL;

        workerinfo = xmalloc(sizeof *workerinfo);
        pthread_setspecific(worker_key, workerinfo);
        workerinfo->fd = p[0];
        
        switch (workerinfo->child = fork()) {
            case 0:
                close(p[0]);
                _exit(forking_resolver_worker(p[1]));

            case -1:
                close(p[0]);
                close(p[1]);
                return NULL;

            default:
                close(p[1]);
        }
    }

    /* Now have a worker to which we can write requests. */
    if (write(workerinfo->fd, addr, sizeof *addr) != sizeof *addr
        || read(workerinfo->fd, name, NAMESIZE) != NAMESIZE) {
        /* Something went wrong. Just kill the child and get on with it. */
        kill(workerinfo->child, SIGKILL);
        wait(NULL);
        close(workerinfo->fd);
        xfree(workerinfo);
        pthread_setspecific(worker_key, NULL);
        *name = 0;
    }
    if (!*name)
        return NULL;
    else
        return xstrdup(name);
}

#else

#   warning No name resolution method specified; name resolution will not work

char *do_resolve(struct addr_storage *addr) {
    return NULL;
}

#endif

void resolver_worker(void* ptr) {
/*    int thread_number = *(int*)ptr;*/
    pthread_mutex_lock(&resolver_queue_mutex);
    sethostent(1);
    while(1) {
        /* Wait until we are told that an address has been added to the 
         * queue. */
        pthread_cond_wait(&resolver_queue_cond, &resolver_queue_mutex);

        /* Keep resolving until the queue is empty */
        while(head != tail) {
            char * hostname;
            struct addr_storage addr = resolve_queue[tail];

            /* mutex always locked at this point */

            tail = (tail + 1) % RESOLVE_QUEUE_LENGTH;

            pthread_mutex_unlock(&resolver_queue_mutex);

            hostname = do_resolve(&addr);

            /*
             * Store the result in ns_hash
             */
            pthread_mutex_lock(&resolver_queue_mutex);

            if(hostname != NULL) {
                char* old;
		union {
		    char **ch_pp;
		    void **void_pp;
		} u_old = { &old };
                if(hash_find(ns_hash, &addr.as_addr6, u_old.void_pp) == HASH_STATUS_OK) {
                    hash_delete(ns_hash, &addr);
                    xfree(old);
                }
                hash_insert(ns_hash, &addr.as_addr6, (void*)hostname);
            }

        }
    }
}

void resolver_initialise() {
    int* n;
    int i;
    pthread_t thread;
    head = tail = 0;

    ns_hash = ns_hash_create();
    
    pthread_mutex_init(&resolver_queue_mutex, NULL);
    pthread_cond_init(&resolver_queue_cond, NULL);

    for(i = 0; i < 2; i++) {
        n = (int*)xmalloc(sizeof *n);
        *n = i;
        pthread_create(&thread, NULL, (void*)&resolver_worker, (void*)n);
    }

}

void resolve(int af, void* addr, char* result, int buflen) {
    char* hostname;
    union {
	char **ch_pp;
	void **void_pp;
    } u_hostname = { &hostname };
    int added = 0;
    struct addr_storage *raddr;

    if(options.dnsresolution == 1) {

        raddr = malloc(sizeof *raddr);
        memset(raddr, 0, sizeof *raddr);
        raddr->af = af;
        raddr->len = (af == AF_INET ? sizeof(struct in_addr)
                      : sizeof(struct in6_addr));
        memcpy(&raddr->addr, addr, raddr->len);

        pthread_mutex_lock(&resolver_queue_mutex);

        if(hash_find(ns_hash, &raddr->as_addr6, u_hostname.void_pp) == HASH_STATUS_OK) {
            /* Found => already resolved, or on the queue, no need to keep
	     * it around */
            free(raddr);
        }
        else {
            hostname = xmalloc(INET6_ADDRSTRLEN);
            inet_ntop(af, &raddr->addr, hostname, INET6_ADDRSTRLEN);

            hash_insert(ns_hash, &raddr->as_addr6, hostname);

            if(((head + 1) % RESOLVE_QUEUE_LENGTH) == tail) {
                /* queue full */
            }
            else if ((af == AF_INET6)
                     && (IN6_IS_ADDR_LINKLOCAL(&raddr->as_addr6)
                         || IN6_IS_ADDR_SITELOCAL(&raddr->as_addr6))) {
                /* Link-local and site-local stay numerical. */
            }
            else {
                resolve_queue[head] = *raddr;
                head = (head + 1) % RESOLVE_QUEUE_LENGTH;
                added = 1;
            }
        }
        pthread_mutex_unlock(&resolver_queue_mutex);

        if(added == 1) {
            pthread_cond_signal(&resolver_queue_cond);
        }

        if(result != NULL && buflen > 1) {
            strncpy(result, hostname, buflen - 1);
            result[buflen - 1] = '\0';
        }
    }
}