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Continue revising RPC service argument example guide

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pierwill 2019-08-26 09:37:33 -05:00
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@ -235,11 +235,11 @@ See below for an example service using an argument.
## Qubes RPC examples
To demostrate some of the possibilities afforded by the qrexec framework, here are two examples of custom RPC services.
To demonstrate some of the possibilities afforded by the qrexec framework, here are two examples of custom RPC services.
### Simple RPC service (addition)
As a demonstration, we can create an RPC service that adds two integers in a target domain (the server, call it "anotherVM") and returns back the result to the invoker (the client, "someVM").
We can create an RPC service that adds two integers in a target domain (the server, call it "anotherVM") and returns back the result to the invoker (the client, "someVM").
In someVM, create a file with the following contents and save it with the path `/usr/bin/our_test_add_client`:
```
@ -289,12 +289,16 @@ We should get "3" as answer.
### RPC service with argument (file reader)
This example uses an [argument](#service-argument-in-policy) to the policy to create an RPC call that reads a specific file from a predefined directory on the target.
<!-- Besides really naive storage, it may be a very simple password manager. -->
Additionally, in this example a simplified workflow will be used - server code placed directly in the service definition file (in `/etc/qubes-rpc` directory).
And no separate client script will be used.
Here we create an RPC call that reads a specific file from a predefined directory on the target.
This example uses an [argument](#service-argument-in-policy) to the policy.
In this example a simplified workflow will be used. The service code placed is placed directly in the service definition file on the target VM.
No separate client script will be needed.
RPC server code (*/etc/qubes-rpc/test.File*)
First, on your target VM, create two files in the home directory: `testfile1` and `testfile2`.
Have them contain two different lines (like "Hello world!" and "Hello world! (2)").
Now place the code below in `/etc/qubes-rpc/test.File` on that same target VM.
This will create and define our RPC service.
```
#!/bin/sh
@ -303,31 +307,35 @@ if [ -z "$argument" ]; then
echo "ERROR: No argument given!"
exit 1
fi
cat "/home/user/rpc-file-storage/$argument"
cat "/home/user/$argument"
```
(The service argument is already sanitized by qrexec framework. It is guaranteed to not contain any spaces or slashes, so there sould be no need for additional path sanitization.)
We'll create three policy files in dom0:
Now we create three policy files in dom0 (see table).
Replace "source_vm1" and others with the names of your own chosen domains.
|------------------------------------------------------------------------|
| Path to file in `dom0` | Policy contents |
|-------------------------------------------+----------------------------|
| /etc/qubes-rpc/policy/test.File | @anyvm @anyvm deny |
| /etc/qubes-rpc/policy/test.File+testfile1 | source_vm1 target_vm allow |
| /etc/qubes-rpc/policy/test.File+testfile2 | source_vm2 target_vm allow |
|------------------------------------------------------------------------|
invoke RPC from `source_vm1` via
With this done, we can run some tests.
Invoke RPC from `source_vm1` via
```
qrexec-client-vm target_vm test.File+testfile1
$ qrexec-client-vm target_vm test.File+testfile1
```
and we should get content of `/home/user/rpc-file-storage/testfile1` as answer.
also possible to invoke RPC from `source_vm2` via
We should get the contents of `/home/user/rpc-file-storage/testfile1`.
Invoking the service from `source_vm2` should work the same, and `testfile2` should also work.
```
qrexec-client-vm target_vm test.File+testfile2
[user@source_vm2] $ qrexec-client-vm target_vm test.File+testfile1
[user@source_vm2] $ qrexec-client-vm target_vm test.File+testfile2
```
But when invoked with other argument or from different VM, it should be denied.