dnsstub.c

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/*
     This file is part of GNUnet.
     Copyright (C) 2012, 2018 GNUnet e.V.
 
     GNUnet is free software: you can redistribute it and/or modify it
     under the terms of the GNU Affero General Public License as published
     by the Free Software Foundation, either version 3 of the License,
     or (at your option) any later version.
 
     GNUnet is distributed in the hope that it will be useful, but
     WITHOUT ANY WARRANTY; without even the implied warranty of
     MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the GNU
     Affero General Public License for more details.
 
     You should have received a copy of the GNU Affero General Public License
     along with this program.  If not, see <http://www.gnu.org/licenses/>.
 
     SPDX-License-Identifier: AGPL3.0-or-later
 */
#include "platform.h"
#include "gnunet_util_lib.h"
 
#define DNS_RETRANSMIT_DELAY \
  GNUNET_TIME_relative_multiply (GNUNET_TIME_UNIT_MILLISECONDS, 250)
 
 
struct DnsServer;
 
 
struct GNUNET_DNSSTUB_RequestSocket
{
  struct GNUNET_NETWORK_Handle *dnsout4;
 
  struct GNUNET_NETWORK_Handle *dnsout6;
 
  GNUNET_DNSSTUB_ResultCallback rc;
 
  void *rc_cls;
 
  struct GNUNET_SCHEDULER_Task *read_task;
 
  struct GNUNET_SCHEDULER_Task *retry_task;
 
  struct DnsServer *ds_pos;
 
  struct GNUNET_DNSSTUB_Context *ctx;
 
  void *request;
 
  size_t request_len;
};
 
 
struct DnsServer
{
  struct DnsServer *next;
 
  struct DnsServer *prev;
 
  struct sockaddr_storage ss;
};
 
 
struct GNUNET_DNSSTUB_Context
{
  struct GNUNET_DNSSTUB_RequestSocket *sockets;
 
  struct DnsServer *dns_head;
 
  struct DnsServer *dns_tail;
 
  struct GNUNET_TIME_Relative retry_freq;
 
  unsigned int num_sockets;
};
 
 
static void
cleanup_rs (struct GNUNET_DNSSTUB_RequestSocket *rs)
{
  if (NULL != rs->dnsout4)
  {
    GNUNET_NETWORK_socket_close (rs->dnsout4);
    rs->dnsout4 = NULL;
  }
  if (NULL != rs->dnsout6)
  {
    GNUNET_NETWORK_socket_close (rs->dnsout6);
    rs->dnsout6 = NULL;
  }
  if (NULL != rs->read_task)
  {
    GNUNET_SCHEDULER_cancel (rs->read_task);
    rs->read_task = NULL;
  }
  if (NULL != rs->retry_task)
  {
    GNUNET_SCHEDULER_cancel (rs->retry_task);
    rs->retry_task = NULL;
  }
  if (NULL != rs->request)
  {
    GNUNET_free (rs->request);
    rs->request = NULL;
  }
}
 
 
static struct GNUNET_NETWORK_Handle *
open_socket (int af)
{
  struct sockaddr_in a4;
  struct sockaddr_in6 a6;
  struct sockaddr *sa;
  socklen_t alen;
  struct GNUNET_NETWORK_Handle *ret;
 
  ret = GNUNET_NETWORK_socket_create (af, SOCK_DGRAM, 0);
  if (NULL == ret)
    return NULL;
  switch (af)
  {
  case AF_INET:
    memset (&a4, 0, alen = sizeof(struct sockaddr_in));
    sa = (struct sockaddr *) &a4;
    break;
 
  case AF_INET6:
    memset (&a6, 0, alen = sizeof(struct sockaddr_in6));
    sa = (struct sockaddr *) &a6;
    break;
 
  default:
    GNUNET_break (0);
    GNUNET_NETWORK_socket_close (ret);
    return NULL;
  }
  sa->sa_family = af;
  if (GNUNET_OK != GNUNET_NETWORK_socket_bind (ret, sa, alen))
  {
    GNUNET_log (GNUNET_ERROR_TYPE_ERROR,
                _ ("Could not bind to any port: %s\n"),
                strerror (errno));
    GNUNET_NETWORK_socket_close (ret);
    return NULL;
  }
  return ret;
}
 
 
static struct GNUNET_DNSSTUB_RequestSocket *
get_request_socket (struct GNUNET_DNSSTUB_Context *ctx)
{
  struct GNUNET_DNSSTUB_RequestSocket *rs;
 
  for (unsigned int i = 0; i < 256; i++)
  {
    rs = &ctx->sockets[GNUNET_CRYPTO_random_u32 (GNUNET_CRYPTO_QUALITY_NONCE,
                                                 ctx->num_sockets)];
    if (NULL == rs->rc)
      break;
  }
  if (NULL != rs->rc)
  {
    /* signal "failure" */
    rs->rc (rs->rc_cls, NULL, 0);
    rs->rc = NULL;
  }
  if (NULL != rs->read_task)
  {
    GNUNET_SCHEDULER_cancel (rs->read_task);
    rs->read_task = NULL;
  }
  if (NULL != rs->retry_task)
  {
    GNUNET_SCHEDULER_cancel (rs->retry_task);
    rs->retry_task = NULL;
  }
  if (NULL != rs->request)
  {
    GNUNET_free (rs->request);
    rs->request = NULL;
  }
  rs->ctx = ctx;
  return rs;
}
 
 
static int
do_dns_read (struct GNUNET_DNSSTUB_RequestSocket *rs,
             struct GNUNET_NETWORK_Handle *dnsout)
{
  struct GNUNET_DNSSTUB_Context *ctx = rs->ctx;
  ssize_t r;
  int len;
 
  if (0 != ioctl (GNUNET_NETWORK_get_fd (dnsout), FIONREAD, &len))
  {
    /* conservative choice: */
    len = UINT16_MAX;
  }
 
  GNUNET_log (GNUNET_ERROR_TYPE_DEBUG, "Receiving %d byte DNS reply\n", len);
  {
    unsigned char buf[len] GNUNET_ALIGN;
    int found;
    struct sockaddr_storage addr;
    socklen_t addrlen;
    struct GNUNET_TUN_DnsHeader *dns;
 
    addrlen = sizeof(addr);
    memset (&addr, 0, sizeof(addr));
    r = GNUNET_NETWORK_socket_recvfrom (dnsout,
                                        buf,
                                        sizeof(buf),
                                        (struct sockaddr *) &addr,
                                        &addrlen);
    if (-1 == r)
    {
      GNUNET_log_strerror (GNUNET_ERROR_TYPE_ERROR, "recvfrom");
      GNUNET_NETWORK_socket_close (dnsout);
      return GNUNET_SYSERR;
    }
    found = GNUNET_NO;
    for (struct DnsServer *ds = ctx->dns_head; NULL != ds; ds = ds->next)
    {
      if (ds->ss.ss_family != addr.ss_family)
        continue;
      if (addr.ss_family == AF_INET)
      {
        struct sockaddr_in *v4 = (struct sockaddr_in *) &addr;
        struct sockaddr_in *ds_v4 = (struct sockaddr_in *) &ds->ss;
 
 
        if ((0 == memcmp (&v4->sin_addr,
                         &ds_v4->sin_addr,
                         sizeof(struct sockaddr_in))) &&
            (v4->sin_port == ds_v4->sin_port))
        {
          found = GNUNET_YES;
          break;
        }
      }
      else
      {
        struct sockaddr_in6 *v6 = (struct sockaddr_in6 *) &addr;
        struct sockaddr_in6 *ds_v6 = (struct sockaddr_in6 *) &ds->ss;
 
        if (0 == memcmp (&v6->sin6_addr,
                         &ds_v6->sin6_addr,
                         sizeof (v6->sin6_addr)) &&
            (v6->sin6_port == ds_v6->sin6_port))
        {
          found = GNUNET_YES;
          break;
        }
 
      }
    }
    if (GNUNET_NO == found)
    {
      GNUNET_log (GNUNET_ERROR_TYPE_DEBUG,
                  "Received DNS response from server we never asked (ignored)\n");
 
      return GNUNET_NO;
    }
    if (sizeof(struct GNUNET_TUN_DnsHeader) > (size_t) r)
    {
      GNUNET_log (GNUNET_ERROR_TYPE_ERROR,
                  _ ("Received DNS response that is too small (%u bytes)\n"),
                  (unsigned int) r);
      return GNUNET_NO;
    }
    dns = (struct GNUNET_TUN_DnsHeader *) buf;
    if (NULL == rs->rc)
    {
      GNUNET_log (GNUNET_ERROR_TYPE_DEBUG,
                  "Request timeout or cancelled; ignoring reply\n");
      return GNUNET_NO;
    }
    rs->rc (rs->rc_cls, dns, r);
  }
  return GNUNET_OK;
}
 
 
static void
read_response (void *cls);
 
 
static void
schedule_read (struct GNUNET_DNSSTUB_RequestSocket *rs)
{
  struct GNUNET_NETWORK_FDSet *rset;
 
  if (NULL != rs->read_task)
    GNUNET_SCHEDULER_cancel (rs->read_task);
  rset = GNUNET_NETWORK_fdset_create ();
  if (NULL != rs->dnsout4)
    GNUNET_NETWORK_fdset_set (rset, rs->dnsout4);
  if (NULL != rs->dnsout6)
    GNUNET_NETWORK_fdset_set (rset, rs->dnsout6);
  rs->read_task =
    GNUNET_SCHEDULER_add_select (GNUNET_SCHEDULER_PRIORITY_DEFAULT,
                                 GNUNET_TIME_UNIT_FOREVER_REL,
                                 rset,
                                 NULL,
                                 &read_response,
                                 rs);
  GNUNET_NETWORK_fdset_destroy (rset);
}
 
 
static void
read_response (void *cls)
{
  struct GNUNET_DNSSTUB_RequestSocket *rs = cls;
  const struct GNUNET_SCHEDULER_TaskContext *tc;
 
  rs->read_task = NULL;
  tc = GNUNET_SCHEDULER_get_task_context ();
  /* read and process ready sockets */
  if ((NULL != rs->dnsout4) &&
      (GNUNET_NETWORK_fdset_isset (tc->read_ready, rs->dnsout4)) &&
      (GNUNET_SYSERR == do_dns_read (rs, rs->dnsout4)))
    rs->dnsout4 = NULL;
  if ((NULL != rs->dnsout6) &&
      (GNUNET_NETWORK_fdset_isset (tc->read_ready, rs->dnsout6)) &&
      (GNUNET_SYSERR == do_dns_read (rs, rs->dnsout6)))
    rs->dnsout6 = NULL;
  /* re-schedule read task */
  schedule_read (rs);
}
 
 
static void
transmit_query (void *cls)
{
  struct GNUNET_DNSSTUB_RequestSocket *rs = cls;
  struct GNUNET_DNSSTUB_Context *ctx = rs->ctx;
  const struct sockaddr *sa;
  socklen_t salen;
  struct DnsServer *ds;
  struct GNUNET_NETWORK_Handle *dnsout;
 
  rs->retry_task =
    GNUNET_SCHEDULER_add_delayed (ctx->retry_freq, &transmit_query, rs);
  ds = rs->ds_pos;
  rs->ds_pos = ds->next;
  if (NULL == rs->ds_pos)
    rs->ds_pos = ctx->dns_head;
  GNUNET_assert (NULL != ds);
  dnsout = NULL;
  switch (ds->ss.ss_family)
  {
  case AF_INET:
    if (NULL == rs->dnsout4)
      rs->dnsout4 = open_socket (AF_INET);
    dnsout = rs->dnsout4;
    sa = (const struct sockaddr *) &ds->ss;
    salen = sizeof(struct sockaddr_in);
    break;
 
  case AF_INET6:
    if (NULL == rs->dnsout6)
      rs->dnsout6 = open_socket (AF_INET6);
    dnsout = rs->dnsout6;
    sa = (const struct sockaddr *) &ds->ss;
    salen = sizeof(struct sockaddr_in6);
    break;
 
  default:
    return;
  }
  if (NULL == dnsout)
  {
    GNUNET_log (GNUNET_ERROR_TYPE_ERROR,
                "Unable to use configure DNS server, skipping\n");
    return;
  }
  if (GNUNET_SYSERR == GNUNET_NETWORK_socket_sendto (dnsout,
                                                     rs->request,
                                                     rs->request_len,
                                                     sa,
                                                     salen))
    GNUNET_log (GNUNET_ERROR_TYPE_WARNING,
                _ ("Failed to send DNS request to %s: %s\n"),
                GNUNET_a2s (sa, salen),
                strerror (errno));
  else
    GNUNET_log (GNUNET_ERROR_TYPE_DEBUG,
                _ ("Sent DNS request to %s\n"),
                GNUNET_a2s (sa, salen));
  schedule_read (rs);
}
 
 
struct GNUNET_DNSSTUB_RequestSocket *
GNUNET_DNSSTUB_resolve (struct GNUNET_DNSSTUB_Context *ctx,
                        const void *request,
                        size_t request_len,
                        GNUNET_DNSSTUB_ResultCallback rc,
                        void *rc_cls)
{
  struct GNUNET_DNSSTUB_RequestSocket *rs;
 
  if (NULL == ctx->dns_head)
  {
    GNUNET_log (GNUNET_ERROR_TYPE_ERROR,
                "No DNS server configured for resolution\n");
    return NULL;
  }
  if (NULL == (rs = get_request_socket (ctx)))
  {
    GNUNET_log (GNUNET_ERROR_TYPE_ERROR,
                "No request socket available for DNS resolution\n");
    return NULL;
  }
  rs->ds_pos = ctx->dns_head;
  rs->rc = rc;
  rs->rc_cls = rc_cls;
  rs->request = GNUNET_memdup (request, request_len);
  rs->request_len = request_len;
  rs->retry_task = GNUNET_SCHEDULER_add_now (&transmit_query, rs);
  return rs;
}
 
 
void
GNUNET_DNSSTUB_resolve_cancel (struct GNUNET_DNSSTUB_RequestSocket *rs)
{
  rs->rc = NULL;
  if (NULL != rs->retry_task)
  {
    GNUNET_SCHEDULER_cancel (rs->retry_task);
    rs->retry_task = NULL;
  }
  if (NULL != rs->read_task)
  {
    GNUNET_SCHEDULER_cancel (rs->read_task);
    rs->read_task = NULL;
  }
}
 
 
struct GNUNET_DNSSTUB_Context *
GNUNET_DNSSTUB_start (unsigned int num_sockets)
{
  struct GNUNET_DNSSTUB_Context *ctx;
 
  if (0 == num_sockets)
  {
    GNUNET_break (0);
    return NULL;
  }
  ctx = GNUNET_new (struct GNUNET_DNSSTUB_Context);
  ctx->num_sockets = num_sockets;
  ctx->sockets =
    GNUNET_new_array (num_sockets, struct GNUNET_DNSSTUB_RequestSocket);
  ctx->retry_freq = DNS_RETRANSMIT_DELAY;
  return ctx;
}
 
 
int
GNUNET_DNSSTUB_add_dns_ip (struct GNUNET_DNSSTUB_Context *ctx,
                           const char *dns_ip)
{
  struct DnsServer *ds;
  struct in_addr i4;
  struct in6_addr i6;
 
  ds = GNUNET_new (struct DnsServer);
  if (1 == inet_pton (AF_INET, dns_ip, &i4))
  {
    struct sockaddr_in *s4 = (struct sockaddr_in *) &ds->ss;
 
    s4->sin_family = AF_INET;
    s4->sin_port = htons (53);
    s4->sin_addr = i4;
#if HAVE_SOCKADDR_IN_SIN_LEN
    s4->sin_len = (u_char) sizeof(struct sockaddr_in);
#endif
  }
  else if (1 == inet_pton (AF_INET6, dns_ip, &i6))
  {
    struct sockaddr_in6 *s6 = (struct sockaddr_in6 *) &ds->ss;
 
    s6->sin6_family = AF_INET6;
    s6->sin6_port = htons (53);
    s6->sin6_addr = i6;
#if HAVE_SOCKADDR_IN_SIN_LEN
    s6->sin6_len = (u_char) sizeof(struct sockaddr_in6);
#endif
  }
  else
  {
    GNUNET_log (GNUNET_ERROR_TYPE_DEBUG,
                "Malformed IP address `%s' for DNS server\n",
                dns_ip);
    GNUNET_free (ds);
    return GNUNET_SYSERR;
  }
  GNUNET_CONTAINER_DLL_insert (ctx->dns_head, ctx->dns_tail, ds);
  return GNUNET_OK;
}
 
 
int
GNUNET_DNSSTUB_add_dns_sa (struct GNUNET_DNSSTUB_Context *ctx,
                           const struct sockaddr *sa)
{
  struct DnsServer *ds;
 
  ds = GNUNET_new (struct DnsServer);
  switch (sa->sa_family)
  {
  case AF_INET :
    GNUNET_memcpy (&ds->ss, sa, sizeof(struct sockaddr_in));
    break;
 
  case AF_INET6:
    GNUNET_memcpy (&ds->ss, sa, sizeof(struct sockaddr_in6));
    break;
 
  default:
    GNUNET_break (0);
    GNUNET_free (ds);
    return GNUNET_SYSERR;
  }
  GNUNET_CONTAINER_DLL_insert (ctx->dns_head, ctx->dns_tail, ds);
  return GNUNET_OK;
}
 
 
void
GNUNET_DNSSTUB_set_retry (struct GNUNET_DNSSTUB_Context *ctx,
                          struct GNUNET_TIME_Relative retry_freq)
{
  ctx->retry_freq = retry_freq;
}
 
 
void
GNUNET_DNSSTUB_stop (struct GNUNET_DNSSTUB_Context *ctx)
{
  struct DnsServer *ds;
 
  while (NULL != (ds = ctx->dns_head))
  {
    GNUNET_CONTAINER_DLL_remove (ctx->dns_head, ctx->dns_tail, ds);
    GNUNET_free (ds);
  }
  for (unsigned int i = 0; i < ctx->num_sockets; i++)
    cleanup_rs (&ctx->sockets[i]);
  GNUNET_free (ctx->sockets);
  GNUNET_free (ctx);
}
 
 
/* end of dnsstub.c */