89 lines
3.7 KiB
Markdown
89 lines
3.7 KiB
Markdown
osmo-remsim - Osmocom remote SIM software suite
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===============================================
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This software suite is a work in progress.
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remsim-client
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-------------
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The client interfaces with GSM phones / modems via dedicated "Card
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Emulation" devices such as the Osmocom SIMtrace2 or sysmocom sysmoQMOD
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board + firmware. This hardware implements the ISO7816-3 electrical
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interface and protocol handling and passes any TPDU headers received
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from the phone/modem to remsim-client for further processing of the
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TPDUs associated to the given APDU transfer.
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remsim-client connects via a RSPRO control connection to remsim-server
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at startup and registers itself. It will receive configuration data
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such as the remsim-bankd IP+Port and the ClientId from remsim-server.
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After receiving the configuration, remsim-client will establish a RSPRO
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data connection to the remsim-bankd IP:Port.
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As the USB interface for remote SIM in simtrace2.git uses one interface
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per slot, we can implement the client in blocking mode, i.e. use
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blocking I/O on the TCP/RSPRO side. This simplifies the code compared
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to a more complex async implementation.
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remsim-bankd
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------------
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The remsim-bankd (SIM Bank Daemon) manages one given SIM bank. The
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initial implementation supports a PC/SC driver to expose any PC/SC
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compatible card readers as SIM bank.
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remsim-bankd initially connects via a RSPRO control connection to
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remsim-server at startup, and will in turn receive a set of initial
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[client,slot]:[bankd,slot] mappings. These mappings determine which
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slot on the client (corresponding to a modem) is mapped to which slot on
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the SIM bank. Mappings can be updated by remsim-server at any given
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point in time.
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remsim-bankd implements a RSPRO server, where it listens to connections
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from remsim-clients.
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As PC/SC only offers a blocking API, there is one thread per PC/SC slot.
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This thread will perform blocking I/O on the socket towards the client,
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and blocking API calls on PC/SC.
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In terms of thread handling, we do:
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* accept() handling in [spare] worker threads
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** this means blocking I/O can be used, as each worker thread only has
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one TCP connection
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** client identifies itself with client:slot
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** lookup mapping based on client:slot (using mutex for protection)
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** open the reader based on the lookup result
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The worker threads initially don't have any mapping to a specific
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reader, and that mapping is only established at a later point after the
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client has identified itself. The advantage is that the entire bankd
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can live without any non-blocking I/O.
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The main thread handles the connection to remsim-server, where it can
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also use non-blocking I/O. However, re-connection would be required, to
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avoid stalling all banks/cards in the event of a connection loss to the
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server.
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worker threads have the following states:
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* INIT (just started)
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* ACCEPTING (they're blocking in the accept() call on the server socket fd)
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* CONNECTED_WAIT_ID (TCP established, but peer not yet identified itself)
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* CONNECTED_CLIENT (TCP established, client has identified itself, no mapping)
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* CONNECTED_CLIENT_MAPPED (TCP established, client has identified itself, mapping exists)
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* CONNECTED_CLIENT_MAPPED_CARD (TCP established, client identified, mapping exists, card opened)
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* CONNECTED_SERVER (TCP established, server has identified itself)
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Once the client disconnects, or any other error occurs (such as card I/O
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errors), the worker thread either returns to INIT state (closing client
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socket and reader), or it terminates. Termination would mean that the
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main thread would have to do non-blocking join to detect client
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termination and then re-spawn clients, so the "return to INIT state"
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approach seems to make more sense.
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Open topics:
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* detecting multiple connections from a server, logging this or even
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avoiding that situation
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