Merge remote-tracking branch 'tor-github/pr/1718/head' into maint-0.4.2

changes/ticket33029

@@ -0,0 +1,5 @@
+  o Major bugfixes (directory authority):
+    - Directory authorities will now send a 503 (not enough bandwidth) code to
+      clients when under bandwidth pressure. Known relays and other authorities
+      will always be answered regardless of the bandwidth situation. Fixes bug
+      33029; bugfix on 0.1.2.5-alpha.

doc/tor.1.txt

@@ -2925,6 +2925,13 @@ on the public Tor network.
     before it will treat advertised bandwidths as wholly
     unreliable. (Default: 500)
 
+[[AuthDirRejectRequestsUnderLoad]] **AuthDirRejectRequestsUnderLoad** **0**|**1**::
+    If set, the directory authority will start rejecting directory requests
+    from non relay connections by sending a 503 error code if it is under
+    bandwidth pressure (reaching the configured limit if any). Relays will
+    always tried to be answered even if this is on. (Default: 1)
+
+
 HIDDEN SERVICE OPTIONS
 ----------------------
 

src/app/config/config.c

@@ -671,6 +671,7 @@ static const config_var_t option_vars_[] = {
   OBSOLETE("UseNTorHandshake"),
   V(User,                        STRING,   NULL),
   OBSOLETE("UserspaceIOCPBuffers"),
+  V(AuthDirRejectRequestsUnderLoad, BOOL,  "1"),
   V(AuthDirSharedRandomness,     BOOL,     "1"),
   V(AuthDirTestEd25519LinkKeys,  BOOL,     "1"),
   OBSOLETE("V1AuthoritativeDirectory"),

src/app/config/or_options_st.h

@@ -1008,6 +1008,13 @@ struct or_options_t {
    */
   uint64_t MaxUnparseableDescSizeToLog;
 
+  /** Bool (default: 1): Under bandwidth pressure, if set to 1, the authority
+   * will always answer directory requests from relays but will start sending
+   * 503 error code for the other connections. If set to 0, all connections
+   * are considered the same and the authority will try to answer them all
+   * regardless of bandwidth pressure or not. */
+  int AuthDirRejectRequestsUnderLoad;
+
   /** Bool (default: 1): Switch for the shared random protocol. Only
    * relevant to a directory authority. If off, the authority won't
    * participate in the protocol. If on (default), a flag is added to the

src/core/mainloop/connection.c

@@ -3051,7 +3051,7 @@ connection_mark_all_noncontrol_connections(void)
  * uses pluggable transports, since we should then limit it even if it
  * comes from an internal IP address. */
 static int
-connection_is_rate_limited(connection_t *conn)
+connection_is_rate_limited(const connection_t *conn)
 {
   const or_options_t *options = get_options();
   if (conn->linked)
@@ -3186,14 +3186,14 @@ connection_bucket_write_limit(connection_t *conn, time_t now)
                                      global_bucket_val, conn_bucket);
 }
 
-/** Return 1 if the global write buckets are low enough that we
+/** Return true iff the global write buckets are low enough that we
  * shouldn't send <b>attempt</b> bytes of low-priority directory stuff
- * out to <b>conn</b>. Else return 0.
-
- * Priority was 1 for v1 requests (directories and running-routers),
- * and 2 for v2 requests and later (statuses and descriptors).
+ * out to <b>conn</b>.
  *
- * There are a lot of parameters we could use here:
+ * If we are a directory authority, always answer dir requests thus true is
+ * always returned.
+ *
+ * Note: There are a lot of parameters we could use here:
  * - global_relayed_write_bucket. Low is bad.
  * - global_write_bucket. Low is bad.
  * - bandwidthrate. Low is bad.
@@ -3205,39 +3205,40 @@ connection_bucket_write_limit(connection_t *conn, time_t now)
  *   mean is "total directory bytes added to outbufs recently", but
  *   that's harder to quantify and harder to keep track of.
  */
-int
-global_write_bucket_low(connection_t *conn, size_t attempt, int priority)
+bool
+connection_dir_is_global_write_low(const connection_t *conn, size_t attempt)
 {
   size_t smaller_bucket =
     MIN(token_bucket_rw_get_write(&global_bucket),
         token_bucket_rw_get_write(&global_relayed_bucket));
-  if (authdir_mode(get_options()) && priority>1)
-    return 0; /* there's always room to answer v2 if we're an auth dir */
+
+  /* Special case for authorities (directory only). */
+  if (authdir_mode_v3(get_options())) {
+    /* Are we configured to possibly reject requests under load? */
+    if (!get_options()->AuthDirRejectRequestsUnderLoad) {
+      /* Answer request no matter what. */
+      return false;
+    }
+    /* Always answer requests from a known relay which includes the other
+     * authorities. The following looks up the addresses for relays that we
+     * have their descriptor _and_ any configured trusted directories. */
+    if (nodelist_probably_contains_address(&conn->addr)) {
+      return false;
+    }
+  }
 
   if (!connection_is_rate_limited(conn))
-    return 0; /* local conns don't get limited */
+    return false; /* local conns don't get limited */
 
   if (smaller_bucket < attempt)
-    return 1; /* not enough space no matter the priority */
+    return true; /* not enough space. */
 
   {
     const time_t diff = approx_time() - write_buckets_last_empty_at;
     if (diff <= 1)
-      return 1; /* we're already hitting our limits, no more please */
+      return true; /* we're already hitting our limits, no more please */
   }
-
-  if (priority == 1) { /* old-style v1 query */
-    /* Could we handle *two* of these requests within the next two seconds? */
-    const or_options_t *options = get_options();
-    size_t can_write = (size_t) (smaller_bucket
-      + 2*(options->RelayBandwidthRate ? options->RelayBandwidthRate :
-           options->BandwidthRate));
-    if (can_write < 2*attempt)
-      return 1;
-  } else { /* v2 query */
-    /* no further constraints yet */
-  }
-  return 0;
+  return false;
 }
 
 /** When did we last tell the accounting subsystem about transmitted

src/core/mainloop/connection.h

@@ -195,8 +195,9 @@ int retry_all_listeners(smartlist_t *new_conns,
 void connection_mark_all_noncontrol_listeners(void);
 void connection_mark_all_noncontrol_connections(void);
 
-ssize_t connection_bucket_write_limit(connection_t *conn, time_t now);
-int global_write_bucket_low(connection_t *conn, size_t attempt, int priority);
+ssize_t connection_bucket_write_limit(struct connection_t *conn, time_t now);
+bool connection_dir_is_global_write_low(const struct connection_t *conn,
+                                        size_t attempt);
 void connection_bucket_init(void);
 void connection_bucket_adjust(const or_options_t *options);
 void connection_bucket_refill_all(time_t now,

src/feature/dircache/dircache.c

@@ -951,7 +951,7 @@ handle_get_current_consensus(dir_connection_t *conn,
     goto done;
   }
 
-  if (global_write_bucket_low(TO_CONN(conn), size_guess, 2)) {
+  if (connection_dir_is_global_write_low(TO_CONN(conn), size_guess)) {
     log_debug(LD_DIRSERV,
               "Client asked for network status lists, but we've been "
               "writing too many bytes lately. Sending 503 Dir busy.");
@@ -1060,7 +1060,7 @@ handle_get_status_vote(dir_connection_t *conn, const get_handler_args_t *args)
         }
       });
 
-    if (global_write_bucket_low(TO_CONN(conn), estimated_len, 2)) {
+    if (connection_dir_is_global_write_low(TO_CONN(conn), estimated_len)) {
       write_short_http_response(conn, 503, "Directory busy, try again later");
       goto vote_done;
     }
@@ -1119,7 +1119,7 @@ handle_get_microdesc(dir_connection_t *conn, const get_handler_args_t *args)
       write_short_http_response(conn, 404, "Not found");
       goto done;
     }
-    if (global_write_bucket_low(TO_CONN(conn), size_guess, 2)) {
+    if (connection_dir_is_global_write_low(TO_CONN(conn), size_guess)) {
       log_info(LD_DIRSERV,
                "Client asked for server descriptors, but we've been "
                "writing too many bytes lately. Sending 503 Dir busy.");
@@ -1217,7 +1217,7 @@ handle_get_descriptor(dir_connection_t *conn, const get_handler_args_t *args)
         msg = "Not found";
       write_short_http_response(conn, 404, msg);
     } else {
-      if (global_write_bucket_low(TO_CONN(conn), size_guess, 2)) {
+      if (connection_dir_is_global_write_low(TO_CONN(conn), size_guess)) {
         log_info(LD_DIRSERV,
                  "Client asked for server descriptors, but we've been "
                  "writing too many bytes lately. Sending 503 Dir busy.");
@@ -1313,9 +1313,8 @@ handle_get_keys(dir_connection_t *conn, const get_handler_args_t *args)
     SMARTLIST_FOREACH(certs, authority_cert_t *, c,
                       len += c->cache_info.signed_descriptor_len);
 
-    if (global_write_bucket_low(TO_CONN(conn),
-                                compress_method != NO_METHOD ? len/2 : len,
-                                2)) {
+    if (connection_dir_is_global_write_low(TO_CONN(conn),
+                                compress_method != NO_METHOD ? len/2 : len)) {
       write_short_http_response(conn, 503, "Directory busy, try again later");
       goto keys_done;
     }

src/feature/nodelist/dirlist.c

@@ -49,6 +49,37 @@ static smartlist_t *trusted_dir_servers = NULL;
  * and all fallback directory servers. */
 static smartlist_t *fallback_dir_servers = NULL;
 
+/** Helper: From a given trusted directory entry, add the v4 or/and v6 address
+ * to the nodelist address set. */
+static void
+add_trusted_dir_to_nodelist_addr_set(const dir_server_t *dir)
+{
+  tor_assert(dir);
+  tor_assert(dir->is_authority);
+
+  /* Add IPv4 and then IPv6 if applicable. */
+  nodelist_add_addr4_to_address_set(dir->addr);
+  if (!tor_addr_is_null(&dir->ipv6_addr)) {
+    nodelist_add_addr6_to_address_set(&dir->ipv6_addr);
+  }
+}
+
+/** Go over the trusted directory server list and add their address(es) to the
+ * nodelist address set. This is called everytime a new consensus is set. */
+MOCK_IMPL(void,
+dirlist_add_trusted_dir_addresses, (void))
+{
+  if (!trusted_dir_servers) {
+    return;
+  }
+
+  SMARTLIST_FOREACH_BEGIN(trusted_dir_servers, const dir_server_t *, ent) {
+    if (ent->is_authority) {
+      add_trusted_dir_to_nodelist_addr_set(ent);
+    }
+  } SMARTLIST_FOREACH_END(ent);
+}
+
 /** Return the number of directory authorities whose type matches some bit set
  * in <b>type</b>  */
 int

src/feature/nodelist/dirlist.h

@@ -44,4 +44,6 @@ void dir_server_add(dir_server_t *ent);
 void clear_dir_servers(void);
 void dirlist_free_all(void);
 
+MOCK_DECL(void, dirlist_add_trusted_dir_addresses, (void));
+
 #endif /* !defined(TOR_DIRLIST_H) */

src/feature/nodelist/nodelist.c

@@ -455,22 +455,43 @@ node_add_to_address_set(const node_t *node)
 
   if (node->rs) {
     if (node->rs->addr)
-      address_set_add_ipv4h(the_nodelist->node_addrs, node->rs->addr);
+      nodelist_add_addr4_to_address_set(node->rs->addr);
     if (!tor_addr_is_null(&node->rs->ipv6_addr))
-      address_set_add(the_nodelist->node_addrs, &node->rs->ipv6_addr);
+      nodelist_add_addr6_to_address_set(&node->rs->ipv6_addr);
   }
   if (node->ri) {
     if (node->ri->addr)
-      address_set_add_ipv4h(the_nodelist->node_addrs, node->ri->addr);
+      nodelist_add_addr4_to_address_set(node->ri->addr);
     if (!tor_addr_is_null(&node->ri->ipv6_addr))
-      address_set_add(the_nodelist->node_addrs, &node->ri->ipv6_addr);
+      nodelist_add_addr6_to_address_set(&node->ri->ipv6_addr);
   }
   if (node->md) {
     if (!tor_addr_is_null(&node->md->ipv6_addr))
-      address_set_add(the_nodelist->node_addrs, &node->md->ipv6_addr);
+      nodelist_add_addr6_to_address_set(&node->md->ipv6_addr);
   }
 }
 
+/** Add the given v4 address into the nodelist address set. */
+void
+nodelist_add_addr4_to_address_set(const uint32_t addr)
+{
+  if (!the_nodelist || !the_nodelist->node_addrs || addr == 0) {
+    return;
+  }
+  address_set_add_ipv4h(the_nodelist->node_addrs, addr);
+}
+
+/** Add the given v6 address into the nodelist address set. */
+void
+nodelist_add_addr6_to_address_set(const tor_addr_t *addr)
+{
+  if (BUG(!addr) || tor_addr_is_null(addr) || tor_addr_is_v4(addr) ||
+      !the_nodelist || !the_nodelist->node_addrs) {
+    return;
+  }
+  address_set_add(the_nodelist->node_addrs, addr);
+}
+
 /** Return true if <b>addr</b> is the address of some node in the nodelist.
  * If not, probably return false. */
 int
@@ -612,9 +633,12 @@ nodelist_set_consensus(networkstatus_t *ns)
   SMARTLIST_FOREACH(the_nodelist->nodes, node_t *, node,
                     node->rs = NULL);
 
-  /* Conservatively estimate that every node will have 2 addresses. */
-  const int estimated_addresses = smartlist_len(ns->routerstatus_list) *
-                                  get_estimated_address_per_node();
+  /* Conservatively estimate that every node will have 2 addresses (v4 and
+   * v6). Then we add the number of configured trusted authorities we have. */
+  int estimated_addresses = smartlist_len(ns->routerstatus_list) *
+                            get_estimated_address_per_node();
+  estimated_addresses += (get_n_authorities(V3_DIRINFO & BRIDGE_DIRINFO) *
+                          get_estimated_address_per_node());
   address_set_free(the_nodelist->node_addrs);
   the_nodelist->node_addrs = address_set_new(estimated_addresses);
 
@@ -665,6 +689,9 @@ nodelist_set_consensus(networkstatus_t *ns)
   SMARTLIST_FOREACH_BEGIN(the_nodelist->nodes, node_t *, node) {
     node_add_to_address_set(node);
   } SMARTLIST_FOREACH_END(node);
+  /* Then, add all trusted configured directories. Some might not be in the
+   * consensus so make sure we know them. */
+  dirlist_add_trusted_dir_addresses();
 
   if (! authdir) {
     SMARTLIST_FOREACH_BEGIN(the_nodelist->nodes, node_t *, node) {

src/feature/nodelist/nodelist.h

@@ -35,6 +35,8 @@ node_t *nodelist_add_microdesc(microdesc_t *md);
 void nodelist_set_consensus(networkstatus_t *ns);
 void nodelist_ensure_freshness(networkstatus_t *ns);
 int nodelist_probably_contains_address(const tor_addr_t *addr);
+void nodelist_add_addr4_to_address_set(const uint32_t addr);
+void nodelist_add_addr6_to_address_set(const tor_addr_t *addr);
 
 void nodelist_remove_microdesc(const char *identity_digest, microdesc_t *md);
 void nodelist_remove_routerinfo(routerinfo_t *ri);

src/test/test_address_set.c

@@ -4,6 +4,7 @@
 #include "core/or/or.h"
 #include "lib/crypt_ops/crypto_rand.h"
 #include "core/or/address_set.h"
+#include "feature/nodelist/dirlist.h"
 #include "feature/nodelist/microdesc.h"
 #include "feature/nodelist/networkstatus.h"
 #include "feature/nodelist/nodelist.h"
@@ -31,6 +32,12 @@ mock_networkstatus_get_latest_consensus_by_flavor(consensus_flavor_t f)
   return dummy_ns;
 }
 
+static void
+mock_dirlist_add_trusted_dir_addresses(void)
+{
+  return;
+}
+
 /* Number of address a single node_t can have. Default to the production
  * value. This is to control the size of the bloom filter. */
 static int addr_per_node = 2;
@@ -98,6 +105,8 @@ test_nodelist(void *arg)
        mock_networkstatus_get_latest_consensus_by_flavor);
   MOCK(get_estimated_address_per_node,
        mock_get_estimated_address_per_node);
+  MOCK(dirlist_add_trusted_dir_addresses,
+       mock_dirlist_add_trusted_dir_addresses);
 
   dummy_ns = tor_malloc_zero(sizeof(*dummy_ns));
   dummy_ns->flavor = FLAV_MICRODESC;
@@ -113,7 +122,10 @@ test_nodelist(void *arg)
    * (the_nodelist->node_addrs) so we will fail the contain test rarely. */
   addr_per_node = 1024;
 
-  /* No node no nothing. The lookups should be empty. */
+  /* No node no nothing. The lookups should be empty. We've mocked the
+   * dirlist_add_trusted_dir_addresses in order for _no_ authorities to be
+   * added to the filter else it makes this test to trigger many false
+   * positive. */
   nodelist_set_consensus(dummy_ns);
 
   /* The address set should be empty. */
@@ -167,6 +179,7 @@ test_nodelist(void *arg)
   UNMOCK(networkstatus_get_latest_consensus);
   UNMOCK(networkstatus_get_latest_consensus_by_flavor);
   UNMOCK(get_estimated_address_per_node);
+  UNMOCK(dirlist_add_trusted_dir_addresses);
 }
 
 struct testcase_t address_set_tests[] = {

src/test/test_bwmgt.c

@@ -6,18 +6,67 @@
  * \brief tests for bandwidth management / token bucket functions
  */
 
+#define CONFIG_PRIVATE
+#define CONNECTION_PRIVATE
 #define TOKEN_BUCKET_PRIVATE
 
 #include "core/or/or.h"
-#include "test/test.h"
 
+#include "app/config/config.h"
+#include "core/mainloop/connection.h"
+#include "feature/dircommon/directory.h"
+#include "feature/nodelist/microdesc.h"
+#include "feature/nodelist/networkstatus.h"
+#include "feature/nodelist/nodelist.h"
+#include "feature/nodelist/routerlist.h"
+#include "lib/crypt_ops/crypto_rand.h"
 #include "lib/evloop/token_bucket.h"
+#include "test/test.h"
+#include "test/test_helpers.h"
+
+#include "app/config/or_options_st.h"
+#include "core/or/connection_st.h"
+#include "feature/nodelist/microdesc_st.h"
+#include "feature/nodelist/networkstatus_st.h"
+#include "feature/nodelist/routerinfo_st.h"
+#include "feature/nodelist/routerstatus_st.h"
 
 // an imaginary time, in timestamp units. Chosen so it will roll over.
 static const uint32_t START_TS = UINT32_MAX-10;
 static const int32_t KB = 1024;
 static const uint32_t GB = (UINT64_C(1) << 30);
 
+static or_options_t mock_options;
+
+static const or_options_t *
+mock_get_options(void)
+{
+  return &mock_options;
+}
+
+static networkstatus_t *dummy_ns = NULL;
+static networkstatus_t *
+mock_networkstatus_get_latest_consensus(void)
+{
+  return dummy_ns;
+}
+
+static networkstatus_t *
+mock_networkstatus_get_latest_consensus_by_flavor(consensus_flavor_t f)
+{
+  tor_assert(f == FLAV_MICRODESC);
+  return dummy_ns;
+}
+
+/* Number of address a single node_t can have. Default to the production
+ * value. This is to control the size of the bloom filter. */
+static int addr_per_node = 2;
+static int
+mock_get_estimated_address_per_node(void)
+{
+  return addr_per_node;
+}
+
 static void
 test_bwmgt_token_buf_init(void *arg)
 {
@@ -220,8 +269,162 @@ test_bwmgt_token_buf_helpers(void *arg)
   ;
 }
 
+static void
+test_bwmgt_dir_conn_global_write_low(void *arg)
+{
+  bool ret;
+  int addr_family;
+  connection_t *conn = NULL;
+  routerstatus_t *rs = NULL; microdesc_t *md = NULL; routerinfo_t *ri = NULL;
+  tor_addr_t relay_addr;
+
+  (void) arg;
+
+  memset(&mock_options, 0, sizeof(or_options_t));
+  MOCK(networkstatus_get_latest_consensus,
+       mock_networkstatus_get_latest_consensus);
+  MOCK(networkstatus_get_latest_consensus_by_flavor,
+       mock_networkstatus_get_latest_consensus_by_flavor);
+  MOCK(get_estimated_address_per_node,
+       mock_get_estimated_address_per_node);
+
+  /*
+   * The following is rather complex but that is what it takes to add a dummy
+   * consensus with a valid routerlist which will populate our node address
+   * set that we need to lookup to test the known relay code path.
+   *
+   * We MUST do that before we MOCK(get_options) else it is another world of
+   * complexity.
+   */
+
+  /* This will be the address of our relay. */
+  tor_addr_parse(&relay_addr, "1.2.3.4");
+
+  /* We'll now add a relay into our routerlist and see if we let it. */
+  dummy_ns = tor_malloc_zero(sizeof(*dummy_ns));
+  dummy_ns->flavor = FLAV_MICRODESC;
+  dummy_ns->routerstatus_list = smartlist_new();
+
+  md = tor_malloc_zero(sizeof(*md));
+  ri = tor_malloc_zero(sizeof(*ri));
+  rs = tor_malloc_zero(sizeof(*rs));
+  crypto_rand(rs->identity_digest, sizeof(rs->identity_digest));
+  crypto_rand(md->digest, sizeof(md->digest));
+  memcpy(rs->descriptor_digest, md->digest, DIGEST256_LEN);
+
+  /* Set IP address. */
+  rs->addr = tor_addr_to_ipv4h(&relay_addr);
+  ri->addr = rs->addr;
+  /* Add the rs to the consensus becoming a node_t. */
+  smartlist_add(dummy_ns->routerstatus_list, rs);
+
+  /* Add all configured authorities (hardcoded) before we set the consensus so
+   * the address set exists. */
+  ret = consider_adding_dir_servers(&mock_options, &mock_options);
+  tt_int_op(ret, OP_EQ, 0);
+
+  /* This will make the nodelist bloom filter very large
+   * (the_nodelist->node_addrs) so we will fail the contain test rarely. */
+  addr_per_node = 1024;
+
+  nodelist_set_consensus(dummy_ns);
+
+  /* Ok, now time to control which options we use. */
+  MOCK(get_options, mock_get_options);
+
+  /* Set ourselves as an authoritative dir. */
+  mock_options.AuthoritativeDir = 1;
+  mock_options.V3AuthoritativeDir = 1;
+  mock_options.UseDefaultFallbackDirs = 0;
+
+  /* This will set our global bucket to 1 byte and thus we will hit the
+   * banwdith limit in our test. */
+  mock_options.BandwidthRate = 1;
+  mock_options.BandwidthBurst = 1;
+
+  /* Else an IPv4 address screams. */
+  mock_options.ClientUseIPv4 = 1;
+  mock_options.ClientUseIPv6 = 1;
+
+  /* Initialize the global buckets. */
+  connection_bucket_init();
+
+  /* The address "127.0.0.1" is set with this helper. */
+  conn = test_conn_get_connection(DIR_CONN_STATE_MIN_, CONN_TYPE_DIR,
+                                  DIR_PURPOSE_MIN_);
+  tt_assert(conn);
+
+  /* First try a non authority non relay IP thus a client but we are not
+   * configured to reject requests under load so we should get a false value
+   * that our limit is _not_ low. */
+  addr_family = tor_addr_parse(&conn->addr, "1.1.1.1");
+  tt_int_op(addr_family, OP_EQ, AF_INET);
+  ret = connection_dir_is_global_write_low(conn, INT_MAX);
+  tt_int_op(ret, OP_EQ, 0);
+
+  /* Now, we will reject requests under load so try again a non authority non
+   * relay IP thus a client. We should get a warning that our limit is too
+   * low. */
+  mock_options.AuthDirRejectRequestsUnderLoad = 1;
+
+  addr_family = tor_addr_parse(&conn->addr, "1.1.1.1");
+  tt_int_op(addr_family, OP_EQ, AF_INET);
+  ret = connection_dir_is_global_write_low(conn, INT_MAX);
+  tt_int_op(ret, OP_EQ, 1);
+
+  /* Now, lets try with a connection address from moria1. It should always
+   * pass even though our limit is too low. */
+  addr_family = tor_addr_parse(&conn->addr, "128.31.0.39");
+  tt_int_op(addr_family, OP_EQ, AF_INET);
+  ret = connection_dir_is_global_write_low(conn, INT_MAX);
+  tt_int_op(ret, OP_EQ, 0);
+
+  /* IPv6 testing of gabelmoo. */
+  addr_family = tor_addr_parse(&conn->addr, "[2001:638:a000:4140::ffff:189]");
+  tt_int_op(addr_family, OP_EQ, AF_INET6);
+  ret = connection_dir_is_global_write_low(conn, INT_MAX);
+  tt_int_op(ret, OP_EQ, 0);
+
+  /* Lets retry with a known relay address. It should pass. Possible due to
+   * our consensus setting above. */
+  memcpy(&conn->addr, &relay_addr, sizeof(tor_addr_t));
+  ret = connection_dir_is_global_write_low(conn, INT_MAX);
+  tt_int_op(ret, OP_EQ, 0);
+
+  /* Lets retry with a random IP that is not an authority nor a relay. */
+  addr_family = tor_addr_parse(&conn->addr, "1.2.3.4");
+  tt_int_op(addr_family, OP_EQ, AF_INET);
+  ret = connection_dir_is_global_write_low(conn, INT_MAX);
+  tt_int_op(ret, OP_EQ, 0);
+
+  /* Finally, just make sure it still denies an IP if we are _not_ a v3
+   * directory authority. */
+  mock_options.V3AuthoritativeDir = 0;
+  addr_family = tor_addr_parse(&conn->addr, "1.2.3.4");
+  tt_int_op(addr_family, OP_EQ, AF_INET);
+  ret = connection_dir_is_global_write_low(conn, INT_MAX);
+  tt_int_op(ret, OP_EQ, 1);
+
+  /* Random IPv6 should not be allowed. */
+  addr_family = tor_addr_parse(&conn->addr, "[CAFE::ACAB]");
+  tt_int_op(addr_family, OP_EQ, AF_INET6);
+  ret = connection_dir_is_global_write_low(conn, INT_MAX);
+  tt_int_op(ret, OP_EQ, 1);
+
+ done:
+  connection_free_minimal(conn);
+  routerstatus_free(rs); routerinfo_free(ri); microdesc_free(md);
+  smartlist_clear(dummy_ns->routerstatus_list);
+  networkstatus_vote_free(dummy_ns);
+
+  UNMOCK(get_estimated_address_per_node);
+  UNMOCK(networkstatus_get_latest_consensus);
+  UNMOCK(networkstatus_get_latest_consensus_by_flavor);
+  UNMOCK(get_options);
+}
+
 #define BWMGT(name)                                          \
-  { #name, test_bwmgt_ ## name , 0, NULL, NULL }
+  { #name, test_bwmgt_ ## name , TT_FORK, NULL, NULL }
 
 struct testcase_t bwmgt_tests[] = {
   BWMGT(token_buf_init),
@@ -229,5 +432,7 @@ struct testcase_t bwmgt_tests[] = {
   BWMGT(token_buf_dec),
   BWMGT(token_buf_refill),
   BWMGT(token_buf_helpers),
+
+  BWMGT(dir_conn_global_write_low),
   END_OF_TESTCASES
 };