tinc/src/node.c
Etienne Dechamps eeebff55c0 Use a splay tree for node UDP addresses in order to avoid collisions.
This commit replaces the node UDP address hash table "cache" with a
full-blown splay tree, aligning it with node_tree (name-indexed) and
node_id_tree (ID-indexed).

I'm doing this for two reasons. The first reason is to make sure we
don't suddenly degrade to O(n) performance when two "hot" nodes end up
in the same hash table bucket (collision).

The second, and most important, reason, has to do with the fact that
the hash table that was being used overrides elements that collide.
Indeed, it turns out that there is one scenario in which the contents of
node_udp_cache has *correctness* implications, not just performance
implications. This has to do with the way handle_incoming_vpn_data() is
implemented.

Assume the following topology:

  A <-> B <-> C

Now let's consider the perspective of tincd running on B, and let's
assume the following is true:

 - All nodes are using the 1.1 protocol with node IDs and relaying
   support.
 - Nodes A and C have UDP addresses that hash to the same value.
 - Node C "wins" in the node_udp_cache (i.e. it overwrites A in the
   cache).
 - Node A has a "dynamic" UDP address (i.e. an UDP address that has been
   detected dynamically and cannot be deduced from edge addresses).

Then, before this commit, A would be unable to relay packets through B.

This is because handle_incoming_vpn_data() will fall back to
try_harder(), which won't be able to match any edge addresses, doesn't
check the dynamic UDP addresses, and won't be able to match any keys
because this is a relayed packet which is encrypted with C's key, not
B's. As a result, tinc will fail to match the source of the packet and
will drop the packet with a "Received UDP packet from unknown source"
message.

I have seen this happen in the wild; it is actually quite likely to
occur when there are more than a handful of nodes because node_udp_cache
only has 256 buckets, making collisions quite likely. This problem is
quite severe because it can completely prevent all packet communication
between nodes - indeed, if node A tries to initiate some communication
with C, it will use relaying at first, until C responds and helps A
establish direct communication with it (e.g. hole punching). If relaying
is broken, C will not help establish direct communication, and as a
result no packets can make it through at all.

The bug can be reproduced fairly easily by reproducing the topology
above while changing the (hardcoded) node_udp_cache size to 1 to force a
collision. One will quickly observe various issues when trying to make A
talk to C. Setting IndirectData on B will make the issue even more
severe and prevent all communication.

Arguably, another way to fix this problem is to make try_harder()
compare the packet's source address to each node's dynamic UDP
addresses. However, I do not like this solution because if two "hot"
nodes are contending on the same hash bucket, try_harder() will be
called very often and packet routing performance will degrade closer to
O(N) (where N is the total number of nodes in the graph). Using a more
appropriate data structure fixes the bug without introducing this
performance problem.
2015-11-04 19:36:02 +00:00

223 lines
5.7 KiB
C

/*
node.c -- node tree management
Copyright (C) 2001-2013 Guus Sliepen <guus@tinc-vpn.org>,
2001-2005 Ivo Timmermans
This program is free software; you can redistribute it and/or modify
it under the terms of the GNU General Public License as published by
the Free Software Foundation; either version 2 of the License, or
(at your option) any later version.
This program 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 General Public License for more details.
You should have received a copy of the GNU General Public License along
with this program; if not, write to the Free Software Foundation, Inc.,
51 Franklin Street, Fifth Floor, Boston, MA 02110-1301 USA.
*/
#include "system.h"
#include "control_common.h"
#include "hash.h"
#include "logger.h"
#include "net.h"
#include "netutl.h"
#include "node.h"
#include "splay_tree.h"
#include "utils.h"
#include "xalloc.h"
#include "ed25519/sha512.h"
splay_tree_t *node_tree;
static splay_tree_t *node_id_tree;
static splay_tree_t *node_udp_tree;
static hash_t *node_id_cache;
node_t *myself;
static int node_compare(const node_t *a, const node_t *b) {
return strcmp(a->name, b->name);
}
static int node_id_compare(const node_t *a, const node_t *b) {
return memcmp(&a->id, &b->id, sizeof(node_id_t));
}
static int node_udp_compare(const node_t *a, const node_t *b) {
int result = sockaddrcmp(&a->address, &b->address);
if (result)
return result;
return (a->name && b->name) ? strcmp(a->name, b->name) : 0;
}
void init_nodes(void) {
node_tree = splay_alloc_tree((splay_compare_t) node_compare, (splay_action_t) free_node);
node_id_tree = splay_alloc_tree((splay_compare_t) node_id_compare, NULL);
node_udp_tree = splay_alloc_tree((splay_compare_t) node_udp_compare, NULL);
node_id_cache = hash_alloc(0x100, sizeof(node_id_t));
}
void exit_nodes(void) {
hash_free(node_id_cache);
splay_delete_tree(node_udp_tree);
splay_delete_tree(node_id_tree);
splay_delete_tree(node_tree);
}
node_t *new_node(void) {
node_t *n = xzalloc(sizeof *n);
if(replaywin) n->late = xzalloc(replaywin);
n->subnet_tree = new_subnet_tree();
n->edge_tree = new_edge_tree();
n->mtu = MTU;
n->maxmtu = MTU;
return n;
}
void free_node(node_t *n) {
if(n->subnet_tree)
free_subnet_tree(n->subnet_tree);
if(n->edge_tree)
free_edge_tree(n->edge_tree);
sockaddrfree(&n->address);
#ifndef DISABLE_LEGACY
cipher_close(n->incipher);
digest_close(n->indigest);
cipher_close(n->outcipher);
digest_close(n->outdigest);
#endif
ecdsa_free(n->ecdsa);
sptps_stop(&n->sptps);
timeout_del(&n->udp_ping_timeout);
if(n->hostname)
free(n->hostname);
if(n->name)
free(n->name);
if(n->late)
free(n->late);
free(n);
}
void node_add(node_t *n) {
unsigned char buf[64];
sha512(n->name, strlen(n->name),buf);
memcpy(&n->id, buf, sizeof n->id);
splay_insert(node_tree, n);
splay_insert(node_id_tree, n);
}
void node_del(node_t *n) {
splay_delete(node_udp_tree, n);
hash_delete(node_id_cache, &n->id);
for splay_each(subnet_t, s, n->subnet_tree)
subnet_del(n, s);
for splay_each(edge_t, e, n->edge_tree)
edge_del(e);
splay_delete(node_id_tree, n);
splay_delete(node_tree, n);
}
node_t *lookup_node(char *name) {
node_t n = {NULL};
n.name = name;
return splay_search(node_tree, &n);
}
node_t *lookup_node_id(const node_id_t *id) {
node_t *n = hash_search(node_id_cache, id);
if(!n) {
node_t tmp = {.id = *id};
n = splay_search(node_id_tree, &tmp);
if(n)
hash_insert(node_id_cache, id, n);
}
return n;
}
node_t *lookup_node_udp(const sockaddr_t *sa) {
node_t tmp = {.address = *sa};
return splay_search(node_udp_tree, &tmp);
}
void update_node_udp(node_t *n, const sockaddr_t *sa) {
if(n == myself) {
logger(DEBUG_ALWAYS, LOG_WARNING, "Trying to update UDP address of myself!");
return;
}
splay_delete(node_udp_tree, n);
if(sa) {
n->address = *sa;
n->sock = 0;
for(int i = 0; i < listen_sockets; i++) {
if(listen_socket[i].sa.sa.sa_family == sa->sa.sa_family) {
n->sock = i;
break;
}
}
splay_insert(node_udp_tree, n);
free(n->hostname);
n->hostname = sockaddr2hostname(&n->address);
logger(DEBUG_PROTOCOL, LOG_DEBUG, "UDP address of %s set to %s", n->name, n->hostname);
}
/* invalidate UDP information - note that this is a security feature as well to make sure
we can't be tricked into flooding any random address with UDP packets */
n->status.udp_confirmed = false;
n->maxrecentlen = 0;
n->mtuprobes = 0;
n->minmtu = 0;
n->maxmtu = MTU;
}
bool dump_nodes(connection_t *c) {
for splay_each(node_t, n, node_tree) {
char id[2 * sizeof n->id + 1];
for (size_t c = 0; c < sizeof n->id; ++c)
sprintf(id + 2 * c, "%02hhx", n->id.x[c]);
id[sizeof id - 1] = 0;
send_request(c, "%d %d %s %s %s %d %d %d %d %x %x %s %s %d %hd %hd %hd %ld", CONTROL, REQ_DUMP_NODES,
n->name, id, n->hostname ?: "unknown port unknown",
#ifdef DISABLE_LEGACY
0, 0, 0,
#else
cipher_get_nid(n->outcipher), digest_get_nid(n->outdigest), (int)digest_length(n->outdigest),
#endif
n->outcompression, n->options, bitfield_to_int(&n->status, sizeof n->status),
n->nexthop ? n->nexthop->name : "-", n->via ? n->via->name ?: "-" : "-", n->distance,
n->mtu, n->minmtu, n->maxmtu, (long)n->last_state_change);
}
return send_request(c, "%d %d", CONTROL, REQ_DUMP_NODES);
}
bool dump_traffic(connection_t *c) {
for splay_each(node_t, n, node_tree)
send_request(c, "%d %d %s %"PRIu64" %"PRIu64" %"PRIu64" %"PRIu64, CONTROL, REQ_DUMP_TRAFFIC,
n->name, n->in_packets, n->in_bytes, n->out_packets, n->out_bytes);
return send_request(c, "%d %d", CONTROL, REQ_DUMP_TRAFFIC);
}