1 files changed, 415 insertions, 0 deletions
diff --git a/src/feature/client/dnsserv.c b/src/feature/client/dnsserv.c
new file mode 100644
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--- /dev/null
+++ b/src/feature/client/dnsserv.c
@@ -0,0 +1,415 @@
+/* Copyright (c) 2007-2018, The Tor Project, Inc. */
+/* See LICENSE for licensing information */
+
+/**
+ * \file dnsserv.c
+ * \brief Implements client-side DNS proxy server code.
+ *
+ * When a user enables the DNSPort configuration option to have their local
+ * Tor client handle DNS requests, this module handles it.  It functions as a
+ * "DNS Server" on the client side, which client applications use.
+ *
+ * Inbound DNS requests are represented as entry_connection_t here (since
+ * that's how Tor represents client-side streams), which are kept associated
+ * with an evdns_server_request structure as exposed by Libevent's
+ * evdns code.
+ *
+ * Upon receiving a DNS request, libevent calls our evdns_server_callback()
+ * function here, which causes this module to create an entry_connection_t
+ * request as appropriate.  Later, when that request is answered,
+ * connection_edge.c calls dnsserv_resolved() so we can finish up and tell the
+ * DNS client.
+ **/
+
+#include "or/or.h"
+#include "or/dnsserv.h"
+#include "or/config.h"
+#include "or/connection.h"
+#include "or/connection_edge.h"
+#include "or/control.h"
+#include "or/main.h"
+#include "or/policies.h"
+
+#include "or/control_connection_st.h"
+#include "or/entry_connection_st.h"
+#include "or/listener_connection_st.h"
+#include "or/socks_request_st.h"
+#include "lib/evloop/compat_libevent.h"
+
+#include <event2/dns.h>
+#include <event2/dns_compat.h>
+/* XXXX this implies we want an improved evdns  */
+#include <event2/dns_struct.h>
+
+/** Helper function: called by evdns whenever the client sends a request to our
+ * DNSPort.  We need to eventually answer the request <b>req</b>.
+ */
+static void
+evdns_server_callback(struct evdns_server_request *req, void *data_)
+{
+  const listener_connection_t *listener = data_;
+  entry_connection_t *entry_conn;
+  edge_connection_t *conn;
+  int i = 0;
+  struct evdns_server_question *q = NULL, *supported_q = NULL;
+  struct sockaddr_storage addr;
+  struct sockaddr *sa;
+  int addrlen;
+  tor_addr_t tor_addr;
+  uint16_t port;
+  int err = DNS_ERR_NONE;
+  char *q_name;
+
+  tor_assert(req);
+
+  log_info(LD_APP, "Got a new DNS request!");
+
+  req->flags |= 0x80; /* set RA */
+
+  /* First, check whether the requesting address matches our SOCKSPolicy. */
+  if ((addrlen = evdns_server_request_get_requesting_addr(req,
+                      (struct sockaddr*)&addr, (socklen_t)sizeof(addr))) < 0) {
+    log_warn(LD_APP, "Couldn't get requesting address.");
+    evdns_server_request_respond(req, DNS_ERR_SERVERFAILED);
+    return;
+  }
+  (void) addrlen;
+  sa = (struct sockaddr*) &addr;
+  if (tor_addr_from_sockaddr(&tor_addr, sa, &port)<0) {
+    log_warn(LD_APP, "Requesting address wasn't recognized.");
+    evdns_server_request_respond(req, DNS_ERR_SERVERFAILED);
+    return;
+  }
+
+  if (!socks_policy_permits_address(&tor_addr)) {
+    log_warn(LD_APP, "Rejecting DNS request from disallowed IP.");
+    evdns_server_request_respond(req, DNS_ERR_REFUSED);
+    return;
+  }
+
+  /* Now, let's find the first actual question of a type we can answer in this
+   * DNS request.  It makes us a little noncompliant to act like this; we
+   * should fix that eventually if it turns out to make a difference for
+   * anybody. */
+  if (req->nquestions == 0) {
+    log_info(LD_APP, "No questions in DNS request; sending back nil reply.");
+    evdns_server_request_respond(req, 0);
+    return;
+  }
+  if (req->nquestions > 1) {
+    log_info(LD_APP, "Got a DNS request with more than one question; I only "
+             "handle one question at a time for now.  Skipping the extras.");
+  }
+  for (i = 0; i < req->nquestions; ++i) {
+    if (req->questions[i]->dns_question_class != EVDNS_CLASS_INET)
+      continue;
+    switch (req->questions[i]->type) {
+      case EVDNS_TYPE_A:
+      case EVDNS_TYPE_AAAA:
+      case EVDNS_TYPE_PTR:
+        /* We always pick the first one of these questions, if there is
+           one. */
+        if (! supported_q)
+          supported_q = req->questions[i];
+        break;
+      default:
+        break;
+      }
+  }
+  if (supported_q)
+    q = supported_q;
+  if (!q) {
+    log_info(LD_APP, "None of the questions we got were ones we're willing "
+             "to support. Sending NOTIMPL.");
+    evdns_server_request_respond(req, DNS_ERR_NOTIMPL);
+    return;
+  }
+
+  /* Make sure the name isn't too long: This should be impossible, I think. */
+  if (err == DNS_ERR_NONE && strlen(q->name) > MAX_SOCKS_ADDR_LEN-1)
+    err = DNS_ERR_FORMAT;
+
+  if (err != DNS_ERR_NONE || !supported_q) {
+    /* We got an error?  There's no question we're willing to answer? Then
+     * send back an answer immediately; we're done. */
+    evdns_server_request_respond(req, err);
+    return;
+  }
+
+  /* Make a new dummy AP connection, and attach the request to it. */
+  entry_conn = entry_connection_new(CONN_TYPE_AP, AF_INET);
+  conn = ENTRY_TO_EDGE_CONN(entry_conn);
+  CONNECTION_AP_EXPECT_NONPENDING(entry_conn);
+  TO_CONN(conn)->state = AP_CONN_STATE_RESOLVE_WAIT;
+  conn->is_dns_request = 1;
+
+  tor_addr_copy(&TO_CONN(conn)->addr, &tor_addr);
+  TO_CONN(conn)->port = port;
+  TO_CONN(conn)->address = tor_addr_to_str_dup(&tor_addr);
+
+  if (q->type == EVDNS_TYPE_A || q->type == EVDNS_TYPE_AAAA ||
+      q->type == EVDNS_QTYPE_ALL) {
+    entry_conn->socks_request->command = SOCKS_COMMAND_RESOLVE;
+  } else {
+    tor_assert(q->type == EVDNS_TYPE_PTR);
+    entry_conn->socks_request->command = SOCKS_COMMAND_RESOLVE_PTR;
+  }
+
+  /* This serves our DNS port so enable DNS request by default. */
+  entry_conn->entry_cfg.dns_request = 1;
+  if (q->type == EVDNS_TYPE_A || q->type == EVDNS_QTYPE_ALL) {
+    entry_conn->entry_cfg.ipv4_traffic = 1;
+    entry_conn->entry_cfg.ipv6_traffic = 0;
+    entry_conn->entry_cfg.prefer_ipv6 = 0;
+  } else if (q->type == EVDNS_TYPE_AAAA) {
+    entry_conn->entry_cfg.ipv4_traffic = 0;
+    entry_conn->entry_cfg.ipv6_traffic = 1;
+    entry_conn->entry_cfg.prefer_ipv6 = 1;
+  }
+
+  strlcpy(entry_conn->socks_request->address, q->name,
+          sizeof(entry_conn->socks_request->address));
+
+  entry_conn->socks_request->listener_type = listener->base_.type;
+  entry_conn->dns_server_request = req;
+  entry_conn->entry_cfg.isolation_flags = listener->entry_cfg.isolation_flags;
+  entry_conn->entry_cfg.session_group = listener->entry_cfg.session_group;
+  entry_conn->nym_epoch = get_signewnym_epoch();
+
+  if (connection_add(ENTRY_TO_CONN(entry_conn)) < 0) {
+    log_warn(LD_APP, "Couldn't register dummy connection for DNS request");
+    evdns_server_request_respond(req, DNS_ERR_SERVERFAILED);
+    connection_free_(ENTRY_TO_CONN(entry_conn));
+    return;
+  }
+
+  control_event_stream_status(entry_conn, STREAM_EVENT_NEW_RESOLVE, 0);
+
+  /* Now, unless a controller asked us to leave streams unattached,
+  * throw the connection over to get rewritten (which will
+  * answer it immediately if it's in the cache, or completely bogus, or
+  * automapped), and then attached to a circuit. */
+  log_info(LD_APP, "Passing request for %s to rewrite_and_attach.",
+           escaped_safe_str_client(q->name));
+  q_name = tor_strdup(q->name); /* q could be freed in rewrite_and_attach */
+  connection_ap_rewrite_and_attach_if_allowed(entry_conn, NULL, NULL);
+  /* Now, the connection is marked if it was bad. */
+
+  log_info(LD_APP, "Passed request for %s to rewrite_and_attach_if_allowed.",
+           escaped_safe_str_client(q_name));
+  tor_free(q_name);
+}
+
+/** Helper function: called whenever the client sends a resolve request to our
+ * controller.  We need to eventually answer the request <b>req</b>.
+ * Returns 0 if the controller will be getting (or has gotten) an event in
+ * response; -1 if we couldn't launch the request.
+ */
+int
+dnsserv_launch_request(const char *name, int reverse,
+                       control_connection_t *control_conn)
+{
+  entry_connection_t *entry_conn;
+  edge_connection_t *conn;
+  char *q_name;
+
+  /* Make a new dummy AP connection, and attach the request to it. */
+  entry_conn = entry_connection_new(CONN_TYPE_AP, AF_INET);
+  entry_conn->entry_cfg.dns_request = 1;
+  conn = ENTRY_TO_EDGE_CONN(entry_conn);
+  CONNECTION_AP_EXPECT_NONPENDING(entry_conn);
+  conn->base_.state = AP_CONN_STATE_RESOLVE_WAIT;
+
+  tor_addr_copy(&TO_CONN(conn)->addr, &control_conn->base_.addr);
+#ifdef AF_UNIX
+  /*
+   * The control connection can be AF_UNIX and if so tor_addr_to_str_dup will
+   * unhelpfully say "<unknown address type>"; say "(Tor_internal)"
+   * instead.
+   */
+  if (control_conn->base_.socket_family == AF_UNIX) {
+    TO_CONN(conn)->port = 0;
+    TO_CONN(conn)->address = tor_strdup("(Tor_internal)");
+  } else {
+    TO_CONN(conn)->port = control_conn->base_.port;
+    TO_CONN(conn)->address = tor_addr_to_str_dup(&control_conn->base_.addr);
+  }
+#else /* !(defined(AF_UNIX)) */
+  TO_CONN(conn)->port = control_conn->base_.port;
+  TO_CONN(conn)->address = tor_addr_to_str_dup(&control_conn->base_.addr);
+#endif /* defined(AF_UNIX) */
+
+  if (reverse)
+    entry_conn->socks_request->command = SOCKS_COMMAND_RESOLVE_PTR;
+  else
+    entry_conn->socks_request->command = SOCKS_COMMAND_RESOLVE;
+
+  conn->is_dns_request = 1;
+
+  strlcpy(entry_conn->socks_request->address, name,
+          sizeof(entry_conn->socks_request->address));
+
+  entry_conn->socks_request->listener_type = CONN_TYPE_CONTROL_LISTENER;
+  entry_conn->original_dest_address = tor_strdup(name);
+  entry_conn->entry_cfg.session_group = SESSION_GROUP_CONTROL_RESOLVE;
+  entry_conn->nym_epoch = get_signewnym_epoch();
+  entry_conn->entry_cfg.isolation_flags = ISO_DEFAULT;
+
+  if (connection_add(TO_CONN(conn))<0) {
+    log_warn(LD_APP, "Couldn't register dummy connection for RESOLVE request");
+    connection_free_(TO_CONN(conn));
+    return -1;
+  }
+
+  control_event_stream_status(entry_conn, STREAM_EVENT_NEW_RESOLVE, 0);
+
+  /* Now, unless a controller asked us to leave streams unattached,
+  * throw the connection over to get rewritten (which will
+  * answer it immediately if it's in the cache, or completely bogus, or
+  * automapped), and then attached to a circuit. */
+  log_info(LD_APP, "Passing request for %s to rewrite_and_attach.",
+           escaped_safe_str_client(name));
+  q_name = tor_strdup(name); /* q could be freed in rewrite_and_attach */
+  connection_ap_rewrite_and_attach_if_allowed(entry_conn, NULL, NULL);
+  /* Now, the connection is marked if it was bad. */
+
+  log_info(LD_APP, "Passed request for %s to rewrite_and_attach_if_allowed.",
+           escaped_safe_str_client(q_name));
+  tor_free(q_name);
+  return 0;
+}
+
+/** If there is a pending request on <b>conn</b> that's waiting for an answer,
+ * send back an error and free the request. */
+void
+dnsserv_reject_request(entry_connection_t *conn)
+{
+  if (conn->dns_server_request) {
+    evdns_server_request_respond(conn->dns_server_request,
+                                 DNS_ERR_SERVERFAILED);
+    conn->dns_server_request = NULL;
+  }
+}
+
+/** Look up the original name that corresponds to 'addr' in req.  We use this
+ * to preserve case in order to facilitate clients using 0x20-hacks to avoid
+ * DNS poisoning. */
+static const char *
+evdns_get_orig_address(const struct evdns_server_request *req,
+                       int rtype, const char *addr)
+{
+  int i, type;
+
+  switch (rtype) {
+  case RESOLVED_TYPE_IPV4:
+    type = EVDNS_TYPE_A;
+    break;
+  case RESOLVED_TYPE_HOSTNAME:
+    type = EVDNS_TYPE_PTR;
+    break;
+  case RESOLVED_TYPE_IPV6:
+    type = EVDNS_TYPE_AAAA;
+    break;
+  case RESOLVED_TYPE_ERROR:
+  case RESOLVED_TYPE_ERROR_TRANSIENT:
+     /* Addr doesn't matter, since we're not sending it back in the reply.*/
+    return addr;
+  default:
+    tor_fragile_assert();
+    return addr;
+  }
+
+  for (i = 0; i < req->nquestions; ++i) {
+    const struct evdns_server_question *q = req->questions[i];
+    if (q->type == type && !strcasecmp(q->name, addr))
+      return q->name;
+  }
+  return addr;
+}
+
+/** Tell the dns request waiting for an answer on <b>conn</b> that we have an
+ * answer of type <b>answer_type</b> (RESOLVE_TYPE_IPV4/IPV6/ERR), of length
+ * <b>answer_len</b>, in <b>answer</b>, with TTL <b>ttl</b>.  Doesn't do
+ * any caching; that's handled elsewhere. */
+void
+dnsserv_resolved(entry_connection_t *conn,
+                 int answer_type,
+                 size_t answer_len,
+                 const char *answer,
+                 int ttl)
+{
+  struct evdns_server_request *req = conn->dns_server_request;
+  const char *name;
+  int err = DNS_ERR_NONE;
+  if (!req)
+    return;
+  name = evdns_get_orig_address(req, answer_type,
+                                conn->socks_request->address);
+
+  /* XXXX Re-do; this is dumb. */
+  if (ttl < 60)
+    ttl = 60;
+
+  /* The evdns interface is: add a bunch of reply items (corresponding to one
+   * or more of the questions in the request); then, call
+   * evdns_server_request_respond. */
+  if (answer_type == RESOLVED_TYPE_IPV6) {
+    evdns_server_request_add_aaaa_reply(req,
+                                        name,
+                                        1, answer, ttl);
+  } else if (answer_type == RESOLVED_TYPE_IPV4 && answer_len == 4 &&
+             conn->socks_request->command == SOCKS_COMMAND_RESOLVE) {
+    evdns_server_request_add_a_reply(req,
+                                     name,
+                                     1, answer, ttl);
+  } else if (answer_type == RESOLVED_TYPE_HOSTNAME &&
+             answer_len < 256 &&
+             conn->socks_request->command == SOCKS_COMMAND_RESOLVE_PTR) {
+    char *ans = tor_strndup(answer, answer_len);
+    evdns_server_request_add_ptr_reply(req, NULL,
+                                       name,
+                                       ans, ttl);
+    tor_free(ans);
+  } else if (answer_type == RESOLVED_TYPE_ERROR) {
+    err = DNS_ERR_NOTEXIST;
+  } else { /* answer_type == RESOLVED_TYPE_ERROR_TRANSIENT */
+    err = DNS_ERR_SERVERFAILED;
+  }
+
+  evdns_server_request_respond(req, err);
+
+  conn->dns_server_request = NULL;
+}
+
+/** Set up the evdns server port for the UDP socket on <b>conn</b>, which
+ * must be an AP_DNS_LISTENER */
+void
+dnsserv_configure_listener(connection_t *conn)
+{
+  listener_connection_t *listener_conn;
+  tor_assert(conn);
+  tor_assert(SOCKET_OK(conn->s));
+  tor_assert(conn->type == CONN_TYPE_AP_DNS_LISTENER);
+
+  listener_conn = TO_LISTENER_CONN(conn);
+  listener_conn->dns_server_port =
+    tor_evdns_add_server_port(conn->s, 0, evdns_server_callback,
+                              listener_conn);
+}
+
+/** Free the evdns server port for <b>conn</b>, which must be an
+ * AP_DNS_LISTENER. */
+void
+dnsserv_close_listener(connection_t *conn)
+{
+  listener_connection_t *listener_conn;
+  tor_assert(conn);
+  tor_assert(conn->type == CONN_TYPE_AP_DNS_LISTENER);
+
+  listener_conn = TO_LISTENER_CONN(conn);
+
+  if (listener_conn->dns_server_port) {
+    evdns_close_server_port(listener_conn->dns_server_port);
+    listener_conn->dns_server_port = NULL;
+  }
+}