Osmocom Remote SIM Software Suite https://osmocom.org/projects/osmo-remsim
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Harald Welte 65006583c1 server: Detect duplicate client/bankd connection; drop new ones
we're dropping the current (new) connection as we don't really know which
is the "right" one. Dropping the new gives the old connection time to
timeout, or to continue to operate.  If we were to drop the old
connection, this could interrupt a perfectly working connection and opens
some kind of DoS.

Related: OS#5527
Change-Id: I00387dbc19d689415470e2f08df08a47a78b81c0
2022-05-03 18:09:14 +02:00
asn1 server: Detect duplicate client/bankd connection; drop new ones 2022-05-03 18:09:14 +02:00
contrib Bump version: → 1.0.0 2021-12-09 09:09:49 +01:00
debian Bump version: → 1.0.0 2021-12-09 09:09:49 +01:00
doc Fix client_id/bank_id/slot_nr range in manual + --help output 2022-01-16 14:35:25 +01:00
ffasn1c add ffasn1c example for RSPRO 2018-09-24 17:46:05 +02:00
include server: Detect duplicate client/bankd connection; drop new ones 2022-05-03 18:09:14 +02:00
src server: Detect duplicate client/bankd connection; drop new ones 2022-05-03 18:09:14 +02:00
.gitignore gitignore: add osmo-remsim-client-reader_conf 2021-06-22 17:40:08 +02:00
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Makefile.am Makefile.am: EXTRA_DIST: debian, contrib/*.spec.in 2020-05-22 14:13:21 +02:00
README.md README.md: add 'osmo-' prefix to remsim-{server,bankd,client} 2019-04-03 17:24:42 +02:00
configure.ac Depend on libosmo-simtrace >= 0.8.0 2021-12-09 08:18:46 +01:00
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libosmo-rspro.pc.in Add libosmo-rspro.pc.in for pkg-config integration 2019-04-03 09:35:48 +02:00
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osmo-remsim - Osmocom remote SIM software suite

This software suite is a work in progress.


The client interfaces with GSM phones / modems via dedicated "Card Emulation" devices such as the Osmocom SIMtrace2 or sysmocom sysmoQMOD board + firmware. This hardware implements the ISO7816-3 electrical interface and protocol handling and passes any TPDU headers received from the phone/modem to osmo-remsim-client for further processing of the TPDUs associated to the given APDU transfer.

osmo-remsim-client connects via a RSPRO control connection to osmo-remsim-server at startup and registers itself. It will receive configuration data such as the osmo-remsim-bankd IP+Port and the ClientId from osmo-remsim-server.

After receiving the configuration, osmo-remsim-client will establish a RSPRO data connection to the osmo-remsim-bankd IP:Port.

As the USB interface for remote SIM in simtrace2.git uses one interface per slot, we can implement the client in blocking mode, i.e. use blocking I/O on the TCP/RSPRO side. This simplifies the code compared to a more complex async implementation.


The osmo-remsim-bankd (SIM Bank Daemon) manages one given SIM bank. The initial implementation supports a PC/SC driver to expose any PC/SC compatible card readers as SIM bank.

osmo-remsim-bankd initially connects via a RSPRO control connection to osmo-remsim-server at startup, and will in turn receive a set of initial [client,slot]:[bankd,slot] mappings. These mappings determine which slot on the client (corresponding to a modem) is mapped to which slot on the SIM bank. Mappings can be updated by osmo-remsim-server at any given point in time.

osmo-remsim-bankd implements a RSPRO server, where it listens to connections from osmo-remsim-clients.

As PC/SC only offers a blocking API, there is one thread per PC/SC slot. This thread will perform blocking I/O on the socket towards the client, and blocking API calls on PC/SC.

In terms of thread handling, we do:

  • accept() handling in [spare] worker threads ** this means blocking I/O can be used, as each worker thread only has one TCP connection ** client identifies itself with client:slot ** lookup mapping based on client:slot (using mutex for protection) ** open the reader based on the lookup result

The worker threads initially don't have any mapping to a specific reader, and that mapping is only established at a later point after the client has identified itself. The advantage is that the entire bankd can live without any non-blocking I/O.

The main thread handles the connection to osmo-remsim-server, where it can also use non-blocking I/O. However, re-connection would be required, to avoid stalling all banks/cards in the event of a connection loss to the server.

worker threads have the following states:

  • INIT (just started)
  • ACCEPTING (they're blocking in the accept() call on the server socket fd)
  • CONNECTED_WAIT_ID (TCP established, but peer not yet identified itself)
  • CONNECTED_CLIENT (TCP established, client has identified itself, no mapping)
  • CONNECTED_CLIENT_MAPPED (TCP established, client has identified itself, mapping exists)
  • CONNECTED_CLIENT_MAPPED_CARD (TCP established, client identified, mapping exists, card opened)
  • CONNECTED_SERVER (TCP established, server has identified itself)

Once the client disconnects, or any other error occurs (such as card I/O errors), the worker thread either returns to INIT state (closing client socket and reader), or it terminates. Termination would mean that the main thread would have to do non-blocking join to detect client termination and then re-spawn clients, so the "return to INIT state" approach seems to make more sense.

Open topics:

  • detecting multiple connections from a server, logging this or even avoiding that situation