3 Commits

Author	SHA1	Message	Date
Simon Tatham	1d323d5c80	Add an actual SSH server program. ... 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).	2018-10-21 10:02:10 +01:00
Simon Tatham	9fe719f47d	Server prep: parse a lot of new channel requests. ... 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.	2018-10-21 10:02:10 +01:00
Simon Tatham	b94c6a7e38	Move client-specific SSH code into new files. ... 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.	2018-10-21 10:02:10 +01:00