Currently, when sending packets over TCP where the final recipient is
a node we have a direct metaconnection to, tinc first establishes a
SPTPS handshake between the two neighbors.
It turns out this SPTPS tunnel is not actually useful, because the
packet is only being sent over one metaconnection with no intermediate
nodes, and the metaconnection itself is already secured using a separate
SPTPS handshake.
Therefore it seems simpler and more efficient to simply send these
packets directly over the metaconnection itself without any additional
layer. This commits implements this solution without any changes to the
metaprotocol, since the appropriate message already exists: it's the
good old "plaintext" PACKET message.
This change brings two significant benefits:
- Packets to neighbors can be sent immediately - there is no initial
delay and packet loss previously caused by the SPTPS handshake;
- Performance of sending packets to neighbors over TCP is greatly
improved since the data only goes through one round of encryption
instead of two.
Conflicts:
src/net_packet.c
Currently, when tinc establishes a metaconnection, it automatically
starts a VPN SPTPS tunnel with the other side of the metaconnection.
It is not clear what this is trying to accomplish. Having a
metaconnection with a node does not necessarily mean we're going to send
packets to that node. This patch removes this behavior, thereby
simplifying code paths and removing unnecessary network chatter.
Naturally, this introduces a slight delay (as well as at least one
initial packet loss) between the moment a metaconnection is established
and the moment VPN packets can be exchanged between the two nodes.
However this is no different to the non-neighbor case, so it makes
things more consistent and therefore easier to reason about.
The offset value indicates where the actual payload starts, so we can
process both legacy and SPTPS UDP packets without having to do casting
tricks and/or moving memory around.
Limit the amount of address/ID lookups to the minimum in all cases:
1) Legacy packets, need an address lookup.
2) Indirect SPTPS packets, need an address lookup + two ID lookups.
3) Direct SPTPS packets, need an ID or an address lookup.
So we start with an address lookup. If the source is an 1.1 node, we know it's an SPTPS packet,
and then the check for direct packets is a simple check if dstid is zero. If not, do the srcid and dstid
lookup. If the source is an 1.0 node, we don't have to do anything else.
If the address is unknown, we first check whether it's from a 1.1 node by assuming it has a valid srcid
and verifying the packet. If not, use the old try_harder().
If the peer presents a different one from the one we already know, log
an error. Otherwise, log an informational message, and terminate in the
same way as we would if we didn't already have that key.
The SPTPS code doesn't know about nodes, so when it logs an error about
a bad packet, it doesn't log which node it came from. So add a log
message with the node's name and hostname in receive_udppacket().
On Linux, tinc doesn't know the MAC address of the TAP device until the
first read. This means that if no packets are sent through the
interface, tinc won't be able to figure out which MAC address to tag
incoming packets with. As a result, it is impossible to receive any
packet until at least one packet has been sent.
When IPv6 is disabled Linux does not spontanously send any packets
when the interface comes up. At first users wonder why the node is not
responding to ICMP pings, and then as soon as at least one packet is
sent through the interface, pings mysteriously start working, resulting
in user confusion.
This change fixes that problem by making sure tinc is aware of the
device's MAC address even before the first packet is sent.
Currently, when tinc sends UDP SPTPS datagrams through a relay, it
doesn't automatically start discovering PMTU with the relay. This means
that unless something else triggers PMTU discovery, tinc will keep using
TCP when sending packets through the relay.
This patches fixes the issue by explicitly establishing UDP tunnels with
relays.
Currently, we send MTU probes to each node we receive a key for, even if
we know we will never send UDP packets to that node because of
indirection. This commit disables MTU probing between nodes that have
direct communication disabled, otherwise MTU probes end up getting sent
through relays.
With the legacy protocol this was never a problem because we would never
request the key of a node with indirection enabled; with SPTPS this was
not a problem until we introduced relaying because send_sptps_data()
would simply ignore indirections, but this is not the case anymore.
Note that the fix is implemented in a quick and dirty way, by disabling
the call to send_mtu_probe() in ans_key_h(); this is not a clean fix
because there's no code to resume sending MTU probes in case the
indirection disappears because of a graph change.
This commit changes the layout of UDP datagrams to include a 6-byte
destination node ID at the very beginning of the datagram (i.e. before
the source node ID and the seqno). Note that this only applies to SPTPS.
Thanks to this new field, it is now possible to send SPTPS datagrams to
nodes that are not the final recipient of the packets, thereby using
these nodes as relay nodes. Previously SPTPS was unable to relay packets
using UDP, and required a fallback to TCP if the final recipient could
not be contacted directly using UDP. In that sense it fixes a regression
that SPTPS introduced with regard to the legacy protocol.
This change also updates tinc's low-level routing logic (i.e.
send_sptps_data()) to automatically use this relaying facility if at all
possible. Specifically, it will relay packets if we don't have a
confirmed UDP link to the final recipient (but we have one with the next
hop node), or if IndirectData is specified. This is similar to how the
legacy protocol forwards packets.
When sending packets directly without any relaying, the sender node uses
a special value for the destination node ID: instead of setting the
field to the ID of the recipient node, it writes a zero ID instead. This
allows the recipient node to distinguish between a relayed packet and a
direct packet, which is important when determining the UDP address of
the sending node.
On the relay side, relay nodes will happily relay packets that have a
destination ID which is non-zero *and* is different from their own,
provided that the source IP address of the packet is known. This is to
prevent abuse by random strangers, since a node can't authenticate the
packets that are being relayed through it.
This change keeps the protocol number from the previous datagram format
change (source IDs), 17.4. Compatibility is still preserved with 1.0 and
with pre-1.1 releases. Note, however, that nodes running this code won't
understand datagrams sent from nodes that only use source IDs and
vice-versa (not that we really care).
There is one caveat: in the current state, there is no way for the
original sender to know what the PMTU is beyond the first hop, and
contrary to the legacy protocol, relay nodes can't apply MSS clamping
because they can't decrypt the relayed packets. This leads to
inefficient scenarios where a reduced PMTU over some link that's part of
the relay path will result in relays falling back to TCP to send packets
to their final destinations.
Another caveat is that once a packet gets sent over TCP, it will use
TCP over the entire path, even if it is technically possible to use UDP
beyond the TCP-only link(s).
Arguably, these two caveats can be fixed by improving the
metaconnection protocol, but that's out of scope for this change. TODOs
are added instead. In any case, this is no worse than before.
In addition, this change increases SPTPS datagram overhead by another
6 bytes for the destination ID, on top of the existing 6-byte overhead
from the source ID.
This commit changes the layout of UDP datagrams to include the 6-byte ID
(i.e. node name hash) of the node that crafted the packet at the very
beginning of the datagram (i.e. before the seqno). Note that this only
applies to SPTPS.
This is implemented at the lowest layer, i.e. in
handle_incoming_vpn_data() and send_sptps_data() functions. Source ID is
added and removed there, in such a way that the upper layers are unaware
of its presence.
This is the first stepping stone towards supporting UDP relaying in
SPTPS, by providing information about the original sender in the packet
itself. Nevertheless, even without relaying this commit already provides
a few benefits such as being able to reliably determine the source node
of a packet in the presence of an unknown source IP address, without
having to painfully go through all node keys. This makes tinc's behavior
much more scalable in this regard.
This change does not break anything with regard to the protocol: It
preserves compatibility with 1.0 and even with older pre-1.1 releases
thanks to a minor protocol version change (17.4). Source ID information
won't be included in packets sent to nodes with minor version < 4.
One drawback, however, is that this change increases SPTPS datagram
overhead by 6 bytes (the size of the source ID itself).
This introduces a new type of identifier for nodes, which complements
node names: node IDs. Node IDs are defined as the first 6 bytes of the
SHA-256 hash of the node name. They will be used in future code in lieu
of node names as unique node identifiers in contexts where space is at
a premium (such as VPN packets).
The semantics of node IDs is that they are supposed to be unique in a
tinc graph; i.e. two different nodes that are part of the same graph
should not have the same ID, otherwise things could break. This
solution provides this guarantee based on realistic probabilities:
indeed, according to the birthday problem, with a 48-bit hash, the
probability of at least one collision is 1e-13 with 10 nodes, 1e-11
with 100 nodes, 1e-9 with 1000 nodes and 1e-7 with 10000 nodes. Things
only start getting hairy with more than 1 million nodes, as the
probability gets over 0.2%.
Currently, when tinc receives an UDP packet from an unexpected address
(i.e. an address different from the node's current address), it just
updates its internal UDP address record and carries on like nothing
happened.
This poses two problems:
- It assumes that the PMTU for the new address is the same as the
old address, which is risky. Packets might get dropped if the PMTU
turns out to be smaller (or if UDP communication on the new address
turns out to be impossible).
- Because the source address in the UDP packet itself is not
authenticated (i.e. it can be forged by an attacker), this
introduces a potential vulnerability by which an attacker with
control over one link can trick a tinc node into dumping its network
traffic to an arbitrary IP address.
This commit fixes the issue by invalidating UDP/PMTU state for a node
when its UDP address changes. This will trigger a temporary fallback
to indirect communication until we get confirmation via PMTU discovery
that the node is indeed sitting at the other end of the new UDP address.
Currently tinc only uses type 2 MTU probe replies if the recipient uses
protocol version 17.3. It should of course support any higher minor
protocol version as well.
In this commit, if a node receives a REQ_PUBKEY message from a node it
doesn't have the key for, it will send a REQ_PUBKEY message in return
*before* sending its own key.
The rationale is to prevent delays when establishing communication
between two nodes that see each other for the first time. These delays
are caused by the first SPTPS packet being dropped on the floor, as
shown in the following typical exchange:
node1: No Ed25519 key known for node2
REQ_PUBKEY ->
<- ANS_PUBKEY
node1: Learned Ed25519 public key from node2
REQ_SPTPS_START ->
node2: No Ed25519 key known for zyklos
<- REQ_PUBKEY
ANS_PUBKEY ->
node2: Learned Ed25519 public key from node1
-- 10-second delay --
node1: No key from node2 after 10 seconds, restarting SPTPS
REQ_SPTPS_START ->
<- SPTPS ->
node1: SPTPS key exchange with node2 succesful
node2: SPTPS key exchange with node1 succesful
With this patch, the following happens instead:
node1: No Ed25519 key known for node2
REQ_PUBKEY ->
node2: Preemptively requesting Ed25519 key for node1
<- REQ_PUBKEY
<- ANS_PUBKEY
ANS_PUBKEY ->
node2: Learned Ed25519 public key from node1
node1: Learned Ed25519 public key from node2
REQ_SPTPS_START ->
<- SPTPS ->
node1: SPTPS key exchange with node2 succesful
node2: SPTPS key exchange with node1 succesful
There are platforms on which it is impossible to rename the TUN/TAP
device. An example is Mac OS X (tuntapx). On these platforms,
specifying the Interface option will not rename the interface, but
the specified name will still be passed to tinc-up scripts and the
like, resulting in potential confusion for the user.
A logic bug was introduced in bd451cfe15
in which running graph() several times with zero reachable nodes had
the effect of calling device_enable() (instead of keeping the device
disabled).
This results in weird behavior when DeviceStandby is enabled, especially
on Windows where calling device_enable() several times in a row corrupts
I/O structures for the device, rendering it unusable.
The Windows build was broken by commit
826ad11e41 which introduced a dependency
on the HOST_NAME_MAX macro, which is not defined on Windows. According
to MSDN for gethostname(), the maximum length of the returned string
is 256 bytes (including the terminating null byte), so let's use that
as a fallback.
Successfully getting an existing variable ("tinc get name") should
not result in an error exitcode (1) from the tinc command.
This changes the result of test/commandline.test from FAIL to PASS.
The handling of TAP-Win32 virtual network device reads that complete
immediately (ReadFile() returns TRUE) is incorrect - instead of
starting a new read, tinc will continue listening for the overlapped
read completion event which will never fire. As a result, tinc stops
receiving packets on the interface.
With newer TAP-Win32 versions (such as the experimental
tap-windows6 9.21.0), tinc is unable to read from the virtual network
device:
Error while reading from (null) {23810A13-BCA9-44CE-94C6-9AEDFBF85736}: No such file or directory
This is because these new drivers apparently don't accept reads when
the device is not in the connected state (media status).
This commit fixes the issue by making sure we start reading no sooner
than when the device is enabled, and that we stop reading when the
device is disabled. This also makes the behavior somewhat cleaner,
because it doesn't make much sense to read from a disabled device
anyway.
Some tinc commands, such as "tinc generate-keys", use the terminal to
ask the user for information. This can be bypassed by making sure
there is no terminal, which is trivial on *nix but might require
jumping through some hoops on Windows depending on how the command is
invoked.
This commit adds a --batch option that ensures tinc will never ask the
user for input, even if it is attached to a terminal.
