This commit includes <stdbool.h> from defs.h and deletes my
traditional definitions of TRUE and FALSE, but other than that, it's a
100% mechanical search-and-replace transforming all uses of TRUE and
FALSE into the C99-standardised lowercase spellings.
No actual types are changed in this commit; that will come next. This
is just getting the noise out of the way, so that subsequent commits
can have a higher proportion of signal.
This server is NOT SECURE! If anyone is reading this commit message,
DO NOT DEPLOY IT IN A HOSTILE-FACING ENVIRONMENT! Its purpose is to
speak the server end of everything PuTTY speaks on the client side, so
that I can test that I haven't broken PuTTY when I reorganise its
code, even things like RSA key exchange or chained auth methods which
it's hard to find a server that speaks at all.
(For this reason, it's declared with [UT] in the Recipe file, so that
it falls into the same category as programs like testbn, which won't
be installed by 'make install'.)
Working title is 'Uppity', partly for 'Universal PuTTY Protocol
Interaction Test Yoke', but mostly because it looks quite like the
word 'PuTTY' with part of it reversed. (Apparently 'test yoke' is a
very rarely used term meaning something not altogether unlike 'test
harness', which is a bit of a stretch, but it'll do.)
It doesn't actually _support_ everything I want yet. At the moment,
it's a proof of concept only. But it has most of the machinery
present, and the parts it's missing - such as chained auth methods -
should be easy enough to add because I've built in the required
flexibility, in the form of an AuthPolicy object which can request
them if it wants to. However, the current AuthPolicy object is
entirely trivial, and will let in any user with the password "weasel".
(Another way in which this is not a production-ready server is that it
also has no interaction with the OS's authentication system. In
particular, it will not only let in any user with the same password,
but it won't even change uid - it will open shells and forwardings
under whatever user id you started it up as.)
Currently, the program can only speak the SSH protocol on its standard
I/O channels (using the new FdSocket facility), so if you want it to
listen on a network port, you'll have to run it from some kind of
separate listening program similar to inetd. For my own tests, I'm not
even doing that: I'm just having PuTTY spawn it as a local proxy
process, which also conveniently eliminates the risk of anyone hostile
connecting to it.
The bulk of the actual code reorganisation is already done by previous
commits, so this change is _mostly_ just dropping in a new set of
server-specific source files alongside the client-specific ones I
created recently. The remaining changes in the shared SSH code are
numerous, but all minor:
- a few extra parameters to BPP and PPL constructors (e.g. 'are you
in server mode?'), and pass both sets of SSH-1 protocol flags from
the login to the connection layer
- in server mode, unconditionally send our version string _before_
waiting for the remote one
- a new hook in the SSH-1 BPP to handle enabling compression in
server mode, where the message exchange works the other way round
- new code in the SSH-2 BPP to do _deferred_ compression the other
way round (the non-deferred version is still nicely symmetric)
- in the SSH-2 transport layer, some adjustments to do key derivation
either way round (swapping round the identifying letters in the
various hash preimages, and making sure to list the KEXINITs in the
right order)
- also in the SSH-2 transport layer, an if statement that controls
whether we send SERVICE_REQUEST and wait for SERVICE_ACCEPT, or
vice versa
- new ConnectionLayer methods for opening outgoing channels for X and
agent forwardings
- new functions in portfwd.c to establish listening sockets suitable
for remote-to-local port forwarding (i.e. not under the direction
of a Conf the way it's done on the client side).
ssh2connection.c now knows how to unmarshal the message formats for
all the channel requests we'll need to handle when we're the server
and a client sends them. Each one is translated into a call to a new
method in the Channel vtable, which is implemented by a trivial
'always fail' routine in every channel type we know about so far.
The vtable method underneath sshfwd_write now takes an is_stderr
parameter, and in SSH-2, this is implemented by having separate stdout
and stderr bufchains in each outgoing channel, and counting the size
of both for the purposes of measuring backlog and so forth.
To avoid making _most_ call sites more verbose, the usual macro
wrapper hasn't changed its API; it just sets is_stderr=FALSE. To use
the new feature, there's an sshfwd_write_ext macro that exposes the
extra parameter.
This is a major code reorganisation in preparation for making this
code base into one that can build an SSH server as well as a client.
(Mostly for purposes of using the server as a regression test suite
for the client, though I have some other possible uses in mind too.
However, it's currently no part of my plan to harden the server to the
point where it can sensibly be deployed in a hostile environment.)
In this preparatory commit, I've broken up the SSH-2 transport and
connection layers, and the SSH-1 connection layer, into multiple
source files, with each layer having its own header file containing
the shared type definitions. In each case, the new source file
contains code that's specific to the client side of the protocol, so
that a new file can be swapped in in its place when building the
server.
Mostly this is just a straightforward moving of code without changing
it very much, but there are a couple of actual changes in the process:
The parsing of SSH-2 global-request and channel open-messages is now
done by a new pair of functions in the client module. For channel
opens, I've invented a new union data type to be the return value from
that function, representing either failure (plus error message),
success (plus Channel instance to manage the new channel), or an
instruction to hand the channel over to a sharing downstream (plus a
pointer to the downstream in question).
Also, the tree234 of remote port forwardings in ssh2connection is now
initialised on first use by the client-specific code, so that's where
its compare function lives. The shared ssh2connection_free() still
takes responsibility for freeing it, but now has to check if it's
non-null first.
The outer shell of the ssh2_lportfwd_open method, for making a
local-to-remote port forwarding, is still centralised in
ssh2connection.c, but the part of it that actually constructs the
outgoing channel-open message has moved into the client code, because
that will have to change depending on whether the channel-open has to
have type direct-tcpip or forwarded-tcpip.
In the SSH-1 connection layer, half the filter_queue method has moved
out into the new client-specific code, but not all of it -
bidirectional channel maintenance messages are still handled
centrally. One exception is SSH_MSG_PORT_OPEN, which can be sent in
both directions, but with subtly different semantics - from server to
client, it's referring to a previously established remote forwarding
(and must be rejected if there isn't one that matches it), but from
client to server it's just a "direct-tcpip" request with no prior
context. So that one is in the client-specific module, and when I add
the server code it will have its own different handler.
Previously, it returned a human-readable string suitable for log
files, which tried to say something useful about the remote end of a
socket. Now it returns a whole SocketPeerInfo structure, of which that
human-friendly log string is just one field, but also some of the same
information - remote IP address and port, in particular - is provided
in machine-readable form where it's available.
Turns out that initiation of a CHANNEL_CLOSE message before both sides
have sent EOF is not only for _unclean_ closures or emergencies; it's
actually a perfectly normal thing that some channel types want to do.
(For example, a channel with a pty at the server end of it has no real
concept of sending EOF independently in both directions: when the pty
master sends EIO, the pty is no longer functioning, and you can no
longer send to it any more than you can receive.)
In SSH-1, the channel system isn't rich enough to represent the
complicated main shell session, so it's all done with a separate set
of custom message types. But PuTTY now abstracts away that difference,
by representing both as different implementations of the SshChannel
class: ssh1channel is for things that the protocol thinks are 'really'
channels, and ssh1mainchan is for the shell session. All the same
methods are implemented, but generate different wire messages.
This means that the logic to decide _when_ to enable X forwarding,
agent forwarding etc is all centralised into mainchan.c, where it
doesn't have to be repeated for both protocol versions.
It also simplifies the final loop in the connection protocol, which no
longer has to contain the code to move data from the user input
bufchain to the channel's output; that's now done by the mainchan
write method, the same as it is in SSH-2 where mainchan is just like
other channels.
I've introduced a new POD struct type 'ssh_ttymodes' which stores an
encoding of everything you can specify in the "pty-req" packet or the
SSH-1 equivalent. This allows me to split up
write_ttymodes_to_packet_from_conf() into two separate functions, one
to parse all the ttymode data out of a Conf (and a Seat for fallback)
and return one of those structures, and the other to write it into an
SSH packet.
While I'm at it, I've moved the special case of terminal speeds into
the same mechanism, simplifying the call sites in both versions of the
SSH protocol.
The new master definition of all terminal modes lives in a header
file, with an ifdef around each item, so that later on I'll be able to
include it in a context that only enumerates the modes supported by
the particular target Unix platform.
This gets another big pile of logic out of ssh2connection and puts it
somewhere more central. Now the only thing left in ssh2connection is
the formatting and parsing of the various channel requests; the logic
deciding which ones to issue and what to do about them is devolved to
the Channel implementation, as it properly should be.
In my future plans, some SshChannels are going to need to be able to
ask favours from the connection layer as a whole. And an SshChannel is
inextricably tied to an instance of the connection layer, so there's
no real reason _not_ to make the pointer generally available.
Each of the new subroutines corresponds to one of the channel types
for which we know how to parse a CHANNEL_OPEN, and has a collection of
parameters corresponding to the fields of that message structure.
ssh2_connection_filter_queue now confines itself to parsing the
message, calling one of those functions, and constructing an
appropriate reply message if any.
The SSH-1 SshChannel vtable didn't bother to provide the
window_override_removed method, because I wrongly remembered that it
was only called when connection sharing. In fact, it's _called_ in any
X forwarding, but it only has to _do_ anything when connection
sharing: SSH-1 has to provide an empty implementation to avoid
segfaulting by calling a null function pointer.
This is a new vtable-based abstraction which is passed to a backend in
place of Frontend, and it implements only the subset of the Frontend
functions needed by a backend. (Many other Frontend functions still
exist, notably the wide range of things called by terminal.c providing
platform-independent operations on the GUI terminal window.)
The purpose of making it a vtable is that this opens up the
possibility of creating a backend as an internal implementation detail
of some other activity, by providing just that one backend with a
custom Seat that implements the methods differently.
For example, this refactoring should make it feasible to directly
implement an SSH proxy type, aka the 'jump host' feature supported by
OpenSSH, aka 'open a secondary SSH session in MAINCHAN_DIRECT_TCP
mode, and then expose the main channel of that as the Socket for the
primary connection'. (Which of course you can already do by spawning
'plink -nc' as a separate proxy process, but this would permit it in
the _same_ process without anything getting confused.)
I've centralised a full set of stub methods in misc.c for the new
abstraction, which allows me to get rid of several annoying stubs in
the previous code. Also, while I'm here, I've moved a lot of
duplicated modalfatalbox() type functions from application main
program files into wincons.c / uxcons.c, which I think saves
duplication overall. (A minor visible effect is that the prefixes on
those console-based fatal error messages will now be more consistent
between applications.)
LogContext is now the owner of the logevent() function that back ends
and so forth are constantly calling. Previously, logevent was owned by
the Frontend, which would store the message into its list for the GUI
Event Log dialog (or print it to standard error, or whatever) and then
pass it _back_ to LogContext to write to the currently open log file.
Now it's the other way round: LogContext gets the message from the
back end first, writes it to its log file if it feels so inclined, and
communicates it back to the front end.
This means that lots of parts of the back end system no longer need to
have a pointer to a full-on Frontend; the only thing they needed it
for was logging, so now they just have a LogContext (which many of
them had to have anyway, e.g. for logging SSH packets or session
traffic).
LogContext itself also doesn't get a full Frontend pointer any more:
it now talks back to the front end via a little vtable of its own
called LogPolicy, which contains the method that passes Event Log
entries through, the old askappend() function that decides whether to
truncate a pre-existing log file, and an emergency function for
printing an especially prominent message if the log file can't be
created. One minor nice effect of this is that console and GUI apps
can implement that last function subtly differently, so that Unix
console apps can write it with a plain \n instead of the \r\n
(harmless but inelegant) that the old centralised implementation
generated.
One other consequence of this is that the LogContext has to be
provided to backend_init() so that it's available to backends from the
instant of creation, rather than being provided via a separate API
call a couple of function calls later, because backends have typically
started doing things that need logging (like making network
connections) before the call to backend_provide_logctx. Fortunately,
there's no case in the whole code base where we don't already have
logctx by the time we make a backend (so I don't actually remember why
I ever delayed providing one). So that shortens the backend API by one
function, which is always nice.
While I'm tidying up, I've also moved the printf-style logeventf() and
the handy logevent_and_free() into logging.c, instead of having copies
of them scattered around other places. This has also let me remove
some stub functions from a couple of outlying applications like
Pageant. Finally, I've removed the pointless "_tag" at the end of
LogContext's official struct name.
Ian Jackson points out that the Linux kernel has a macro of this name
with the same purpose, and suggests that it's a good idea to use the
same name as they do, so that at least some people reading one code
base might recognise it from the other.
I never really thought very hard about what order FROMFIELD's
parameters should go in, and therefore I'm pleasantly surprised to
find that my order agrees with the kernel's, so I don't have to
permute every call site as part of making this change :-)
All the main backend structures - Ssh, Telnet, Pty, Serial etc - now
describe structure types themselves rather than pointers to them. The
same goes for the codebase-wide trait types Socket and Plug, and the
supporting types SockAddr and Pinger.
All those things that were typedefed as pointers are older types; the
newer ones have the explicit * at the point of use, because that's
what I now seem to be preferring. But whichever one of those is
better, inconsistently using a mixture of the two styles is worse, so
let's make everything consistent.
A few types are still implicitly pointers, such as Bignum and some of
the GSSAPI types; generally this is either because they have to be
void *, or because they're typedefed differently on different
platforms and aren't always pointers at all. Can't be helped. But I've
got rid of the main ones, at least.
The check_termination function in ssh2connection is supposed to be
called whenever it's possible that we've run out of (a) channels, and
(b) sharing downstreams. I've been calling it on every channel close,
but apparently completely forgot to add a callback from sshshare.c
that also arranges to call it when we run out of downstreams.
When the connection layer is ready to receive user input, it sets the
flag causing ssh_ppl_want_user_input to return true. But one thing it
_didn't_ do was to check whether the user input bufchain already had
some data in it because the user had typed ahead of the session setup,
and send that input immediately if so. Now it does.
I've tried to separate out as many individually coherent changes from
this work as I could into their own commits, but here's where I run
out and have to commit the rest of this major refactoring as a
big-bang change.
Most of ssh.c is now no longer in ssh.c: all five of the main
coroutines that handle layers of the SSH-1 and SSH-2 protocols now
each have their own source file to live in, and a lot of the
supporting functions have moved into the appropriate one of those too.
The new abstraction is a vtable called 'PacketProtocolLayer', which
has an input and output packet queue. Each layer's main coroutine is
invoked from the method ssh_ppl_process_queue(), which is usually
(though not exclusively) triggered automatically when things are
pushed on the input queue. In SSH-2, the base layer is the transport
protocol, and it contains a pair of subsidiary queues by which it
passes some of its packets to the higher SSH-2 layers - first userauth
and then connection, which are peers at the same level, with the
former abdicating in favour of the latter at the appropriate moment.
SSH-1 is simpler: the whole login phase of the protocol (crypto setup
and authentication) is all in one module, and since SSH-1 has no
repeat key exchange, that setup layer abdicates in favour of the
connection phase when it's done.
ssh.c itself is now about a tenth of its old size (which all by itself
is cause for celebration!). Its main job is to set up all the layers,
hook them up to each other and to the BPP, and to funnel data back and
forth between that collection of modules and external things such as
the network and the terminal. Once it's set up a collection of packet
protocol layers, it communicates with them partly by calling methods
of the base layer (and if that's ssh2transport then it will delegate
some functionality to the corresponding methods of its higher layer),
and partly by talking directly to the connection layer no matter where
it is in the stack by means of the separate ConnectionLayer vtable
which I introduced in commit 8001dd4cb, and to which I've now added
quite a few extra methods replacing services that used to be internal
function calls within ssh.c.
(One effect of this is that the SSH-1 and SSH-2 channel storage is now
no longer shared - there are distinct struct types ssh1_channel and
ssh2_channel. That means a bit more code duplication, but on the plus
side, a lot fewer confusing conditionals in the middle of half-shared
functions, and less risk of a piece of SSH-1 escaping into SSH-2 or
vice versa, which I remember has happened at least once in the past.)
The bulk of this commit introduces the five new source files, their
common header sshppl.h and some shared supporting routines in
sshcommon.c, and rewrites nearly all of ssh.c itself. But it also
includes a couple of other changes that I couldn't separate easily
enough:
Firstly, there's a new handling for socket EOF, in which ssh.c sets an
'input_eof' flag in the BPP, and that responds by checking a flag that
tells it whether to report the EOF as an error or not. (This is the
main reason for those new BPP_READ / BPP_WAITFOR macros - they can
check the EOF flag every time the coroutine is resumed.)
Secondly, the error reporting itself is changed around again. I'd
expected to put some data fields in the public PacketProtocolLayer
structure that it could set to report errors in the same way as the
BPPs have been doing, but in the end, I decided propagating all those
data fields around was a pain and that even the BPPs shouldn't have
been doing it that way. So I've reverted to a system where everything
calls back to functions in ssh.c itself to report any connection-
ending condition. But there's a new family of those functions,
categorising the possible such conditions by semantics, and each one
has a different set of detailed effects (e.g. how rudely to close the
network connection, what exit status should be passed back to the
whole application, whether to send a disconnect message and/or display
a GUI error box).
I don't expect this to be immediately perfect: of course, the code has
been through a big upheaval, new bugs are expected, and I haven't been
able to do a full job of testing (e.g. I haven't tested every auth or
kex method). But I've checked that it _basically_ works - both SSH
protocols, all the different kinds of forwarding channel, more than
one auth method, Windows and Linux, connection sharing - and I think
it's now at the point where the easiest way to find further bugs is to
let it out into the wild and see what users can spot.
