If the Port statement is not used, there are two other ways to let tinc listen
on a non-default port: either by specifying one or more BindToAddress
statements including port numbers, or by starting it from systemd with socket
activation. Tinc announces its own port to other nodes, but before it only
announced what was set using the Port statement.
It seems like a lot of overhead to call access() for every possible extension
defined in PATHEXT, but apparently this is what Windows does itself too. At
least this avoids calling system() when the script one is looking for does not
exist at all.
Since the tinc utility also needs to call scripts, execute_script() is now
split off into its own source file.
The order in which tinc initialized things was not completely correct. Now, it
is done as follows:
- Load and parse configuration files.
- Create all TCP and UDP listening sockets.
- Create PID file and UNIX socket.
- Run the tinc-up script.
- Drop privileges.
- Start outgoing connections.
- Run the main loop.
The PID file can only be created correctly if the listening sockets have been
set up ,as it includes the address and port of the first listening socket. The
tinc-up script has to be run after the PID file and UNIX socket have been
created so it can change their permissions if necessary. Outgoing connections
should only be started right before the main loop, because this is not really
part of the initialization.
The PID file was created before tinc-up was called, but the UNIX socket was
created afterwards, which meant one could not change the UNIX socket's owner or
permissions from the tinc-up script.
As mentioned by Erik Tews, calling fchmod() after fopen() leaves a small window
for exploits. As long as tinc is single-threaded, we can use umask() instead to
reduce file permissions. This also works when creating the AF_UNIX control socket.
The umask of the user running tinc(d) is used for most files, except for the
private keys, invitation files, PID file and control socket.
Tinc now strictly limits incoming connections from the same host to 1 per
second. For incoming connections from multiple hosts short bursts of incoming
connections are allowed (by default 100), but on average also only 1 connection
per second is allowed.
When an incoming connection exceeds the limit, tinc will keep the connection in
a tarpit; the connection will be kept open but it is ignored completely. Only
one connection is in a tarpit at a time to limit the number of useless open
connections.
When LocalDiscovery is enabled, tinc normally sends broadcast packets during
PMTU discovery to the broadcast address (255.255.255.255 or ff02::1). This
option lets tinc use a different address.
At the moment only one LocalDiscoveryAddress can be specified.
Using the tinc command, an administrator of an existing VPN can generate
invitations for new nodes. The invitation is a small URL that can easily
be copy&pasted into email or live chat. Another person can have tinc
automatically setup the necessary configuration files and exchange keys
with the server, by only using the invitation URL.
The invitation protocol uses temporary ECDSA keys. The invitation URL
consists of the hostname and port of the server, a hash of the server's
temporary ECDSA key and a cookie. When the client wants to accept an
invitation, it also creates a temporary ECDSA key, connects to the server
and says it wants to accept an invitation. Both sides exchange their
temporary keys. The client verifies that the server's key matches the hash
in the invitation URL. After setting up an SPTPS connection using the
temporary keys, the client gives the cookie to the server. If the cookie
is valid, the server sends the client an invitation file containing the
client's new name and a copy of the server's host config file. If everything
is ok, the client will generate a long-term ECDSA key and send it to the
server, which will add it to a new host config file for the client.
The invitation protocol currently allows multiple host config files to be
send from the server to the client. However, the client filters out
most configuration variables for its own host configuration file. In
particular, it only accepts Name, Mode, Broadcast, ConnectTo, Subnet and
AutoConnect. Also, at the moment no tinc-up script is generated.
When an invitation has succesfully been accepted, the client needs to start
the tinc daemon manually.
At this point, c->config_tree may or may not be NULL, but this does not tell us whether it is an
outgoing connection or not. For incoming connections, we do not know the peer's name yet,
so we always have to claim ECDSA support. For outgoing connections, we always need to check
whether we have the peer's ECDSA public key, so that if we don't, we correctly tell the peer that
we want to upgrade.
This gets rid of the rest of the symbolic links. However, as a consequence, the
crypto header files have now moved to src/, and can no longer contain
library-specific declarations. Therefore, cipher_t, digest_t, ecdh_t, ecdsa_t
and rsa_t are now all opaque types, and only pointers to those types can be
used.
Normally all requests sent via the meta connections are checked so that they
cannot be larger than the input buffer. However, when packets are forwarded via
meta connections, they are copied into a packet buffer without checking whether
it fits into it. Since the packet buffer is allocated on the stack, this in
effect allows an authenticated remote node to cause a stack overflow.
This issue was found by Martin Schobert.
There are several reasons for this:
- MacOS/X doesn't support polling the tap device using kqueue, requiring a
workaround to fall back to select().
- On Windows only sockets are properly handled, therefore tinc uses a second
thread that does a blocking ReadFile() on the TAP-Win32/64 device. However,
this does not mix well with libevent.
- Libevent, event just the core, is quite large, and although it is easy to get
and install on many platforms, it can be a burden.
- Libev is more lightweight and seems technically superior, but it doesn't
abstract away all the platform differences (for example, async events are not
supported on Windows).
When set to a non-zero value, tinc will try to maintain exactly that number of
meta connections to other nodes. If there are not enough connections, it will
periodically try to set up an outgoing connection to a random node. If there
are too many connections, it will periodically try to remove an outgoing
connection.
The tree functions were never used on the connection_tree, a list is more appropriate.
Also be more paranoid about connections disappearing while traversing the list.
When the Proxy option is used, outgoing connections will be made via the
specified proxy. There is no support for authentication methods or for having
the proxy forward incoming connections, and there is no attempt to proxy UDP.
When the "Broadcast = direct" option is used, broadcast packets are not sent
and forwarded via the Minimum Spanning Tree to all nodes, but are sent directly
to all nodes that can be reached in one hop.
One use for this is to allow running ad-hoc routing protocols, such as OLSR, on
top of tinc.
Most likeley the error is that there just is no valid key inside the used
host file, and in this case errno just contains a random value from the
last previously failed call.
When the Name starts with a $, the rest will be interpreted as the name of an
environment variable containing the real Name. When Name is $HOST, but this
environment variable does not exist, gethostname() will be used to set the
Name. In both cases, illegal characters will be converted to underscores.
If the LISTEN_FDS environment variable is set and tinc is run in the
foreground, tinc will use filedescriptors 3 to 3 + LISTEN_FDS for its listening
TCP sockets. For now, tinc will create matching listening UDP sockets itself.
There is no dependency on systemd or on libsystemd-daemon.
DeviceType = multicast allows one to specify a multicast address and port with
a Device statement. Tinc will then read/send packets to that multicast group
instead of to a tun/tap device. This allows interaction with UML, QEMU and KVM
instances that are listening on the same group.
This allows tincctl to receive log messages from a running tincd,
independent of what is logged to syslog or to file. Tincctl can receive
debug messages with an arbitrary level.
The Broadcast option can be used to cause tinc to drop all broadcast and
multicast packets. This option might be expanded in the future to selectively
allow only some broadcast packet types.
Tinc will now, by default, decrement the TTL field of incoming IPv4 and IPv6
packets, before forwarding them to the virtual network device or to another
node. Packets with a TTL value of zero will be dropped, and an ICMP Time
Exceeded message will be sent back.
This behaviour can be disabled using the DecrementTTL option.
Apart from the platform specific tun/tap driver, link with the dummy and
raw_socket devices, and optionally with support for UML and VDE devices.
At runtime, the DeviceType option can be used to select which driver to
use.
In case the config file could not be opened a new but unitialized RSA structure
would be returned, causing a segmentation fault later on. This would only
happen in the case that the config file could be opened before, but not when
read_rsa_public_key() was called. This situation could occur when the --user
option was used, and the config files were not readable by the specified user.
With some exceptions, tinc only accepted host configuration options for the
local node from the corresponding host configuration file. Although this is
documented, many people expect that they can also put those options in
tinc.conf. Tinc now internally merges the contents of both tinc.conf and the
local host configuration file.
If one uses a symbolic name for the Port option, tinc will send that name
literally to other nodes. However, it is not guaranteed that all nodes have
the same contents in /etc/services, or have such a file at all.
