2 Commits

Author	SHA1	Message	Date
Simon Tatham	cd8a7181fd	Complete rework of terminal userpass input system. ... The system for handling seat_get_userpass_input has always been structured differently between GUI PuTTY and CLI tools like Plink. In the CLI tools, password input is read directly from the OS terminal/console device by console_get_userpass_input; this means that you need to ensure the same terminal input data _hasn't_ already been consumed by the main event loop and sent on to the backend. This is achieved by the backend_sendok() method, which tells the event loop when the backend has finished issuing password prompts, and hence, when it's safe to start passing standard input to backend_send(). But in the GUI tools, input generated by the terminal window has always been sent straight to backend_send(), regardless of whether backend_sendok() says it wants it. So the terminal-based implementation of username and password prompts has to work by consuming input data that had _already_ been passed to the backend - hence, any backend that needs to do that must keep its input on a bufchain, and pass that bufchain to seat_get_userpass_input. It's awkward that these two totally different systems coexist in the first place. And now that SSH proxying needs to present interactive prompts of its own, it's clear which one should win: the CLI style is the Right Thing. So this change reworks the GUI side of the mechanism to be more similar: terminal data now goes into a queue in the Ldisc, and is not sent on to the backend until the backend says it's ready for it via backend_sendok(). So terminal-based userpass prompts can now consume data directly from that queue during the connection setup stage. As a result, the 'bufchain *' parameter has vanished from all the userpass_input functions (both the official implementations of the Seat trait method, and term_get_userpass_input() to which some of those implementations delegate). The only function that actually used that bufchain, namely term_get_userpass_input(), now instead reads from the ldisc's input queue via a couple of new Ldisc functions. (Not _trivial_ functions, since input buffered by Ldisc can be a mixture of raw bytes and session specials like SS_EOL! The input queue inside Ldisc is a bufchain containing a fiddly binary encoding that can represent an arbitrary interleaving of those things.) This greatly simplifies the calls to seat_get_userpass_input in backends, which now don't have to mess about with passing their own user_input bufchain around, or toggling their want_user_input flag back and forth to request data to put on to that bufchain. But the flip side is that now there has to be some _other_ method for notifying the terminal when there's more input to be consumed during an interactive prompt, and for notifying the backend when prompt input has finished so that it can proceed to the next stage of the protocol. This is done by a pair of extra callbacks: when more data is put on to Ldisc's input queue, it triggers a call to term_get_userpass_input, and when term_get_userpass_input finishes, it calls a callback function provided in the prompts_t. Therefore, any use of a prompts_t which *might* be asynchronous must fill in the latter callback when setting up the prompts_t. In SSH, the callback is centralised into a common PPL helper function, which reinvokes the same PPL's process_queue coroutine; in rlogin we have to set it up ourselves. I'm sorry for this large and sprawling patch: I tried fairly hard to break it up into individually comprehensible sub-patches, but I just couldn't tease out any part of it that would stand sensibly alone.	2021-09-14 13:19:33 +01:00
Simon Tatham	6d272ee007	Allow new_connection to take an optional Seat. (NFC) ... This is working towards allowing the subsidiary SSH connection in an SshProxy to share the main user-facing Seat, so as to be able to pass through interactive prompts. This is more difficult than the similar change with LogPolicy, because Seats are stateful. In particular, the trust-sigil status will need to be controlled by the SshProxy until it's ready to pass over control to the main SSH (or whatever) connection. To make this work, I've introduced a thing called a TempSeat, which is (yet) another Seat implementation. When a backend hands its Seat to new_connection(), it does it in a way that allows new_connection() to borrow it completely, and replace it in the main backend structure with a TempSeat, which acts as a temporary placeholder. If the main backend tries to do things like changing trust status or sending output, the TempSeat will buffer them; later on, when the connection is established, TempSeat will replay the changes into the real Seat. So, in each backend, I've made the following changes: - pass &foo->seat to new_connection, which may overwrite it with a TempSeat. - if it has done so (which we can tell via the is_tempseat() query function), then we have to free the TempSeat and reinstate our main Seat. The signal that we can do so is the PLUGLOG_CONNECT_SUCCESS notification, which indicates that SshProxy has finished all its connection setup work. - we also have to remember to free the TempSeat if our backend is disposed of without that having happened (e.g. because the connection _doesn't_ succeed). - in backends which have no local auth phase to worry about, ensure we don't call seat_set_trust_status on the main Seat _before_ it gets potentially replaced with a TempSeat. Moved some calls of seat_set_trust_status to just after new_connection(), so that now the initial trust status setup will go into the TempSeat (if appropriate) and be buffered until that seat is relinquished. In all other uses of new_connection, where we don't have a Seat available at all, we just pass NULL. This is NFC, because neither new_connection() nor any of its delegates will _actually_ do this replacement yet. We're just setting up the framework to enable it to do so in the next commit.	2021-09-13 17:24:47 +01:00