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Reformat code blocks in qrexec.md
Use backticks for all code examples in qrexec docs Also use hyphens for unordered lists
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pierwill
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@ -44,7 +44,9 @@ Once this channel is established, stdin/stdout/stderr from the VMprocess is pass
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The `qrexec-client` command is used to make connections to VMs from dom0.
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For example, the following command
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$ qrexec-client -e -d someVM user:'touch hello-world.txt'
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```
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$ qrexec-client -e -d someVM user:'touch hello-world.txt'
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```
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creates an empty file called `hello-world.txt` in the home folder of `someVM`.
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@ -53,7 +55,9 @@ The `-e` flag tells `qrexec-client` to exit immediately after sending the execut
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With this option, no further data is passed between the domains.
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By contrast, the following command demonstrates an open channel between dom0 and someVM (in this case, a remote shell):
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$ qrexec-client -d someVM user:bash
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```
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$ qrexec-client -d someVM user:bash
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```
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The `qvm-run` command is heavily based on `qrexec-client`.
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It also takes care of additional activities, e.g. starting the domain if it is not up yet and starting the GUI daemon.
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@ -89,7 +93,9 @@ The dom0 directory `/etc/qubes-rpc/policy/` contains a file for each available R
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Together the contents of these files make up the RPC access policy database.
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Policies are defined in lines with the following format:
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srcvm destvm (allow|deny|ask[,default_target=default_target_VM])[,user=user_to_run_as][,target=VM_to_redirect_to]
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```
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srcvm destvm (allow|deny|ask[,default_target=default_target_VM])[,user=user_to_run_as][,target=VM_to_redirect_to]
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```
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You can specify srcvm and destvm by name or by one of the reserved keywords such as `@anyvm`, `@dispvm`, or `dom0`.
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(Of these three, only `@anyvm` keyword makes sense in the srcvm field.
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@ -109,36 +115,46 @@ In the target VM, the file `/etc/qubes-rpc/RPC_ACTION_NAME` must exist, containi
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From outside of dom0, RPC calls take the following form:
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$ qrexec-client-vm target_vm_name RPC_ACTION_NAME rpc_client_path client arguments
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```
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$ qrexec-client-vm target_vm_name RPC_ACTION_NAME rpc_client_path client arguments
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```
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For example:
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$ qrexec-client-vm work qubes.StartApp+firefox
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```
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$ qrexec-client-vm work qubes.StartApp+firefox
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```
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Note that only stdin/stdout is passed between RPC server and client -- notably, no command line arguments are passed.
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By default, stderr of client and server is logged in the syslog/journald of the VM where the process is running.
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It is also possible to call service without specific client program -- in which case server stdin/out will be connected with the terminal:
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$ qrexec-client-vm target_vm_name RPC_ACTION_NAME
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```
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$ qrexec-client-vm target_vm_name RPC_ACTION_NAME
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```
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### Specifying VMs: tags, types, targets, etc.
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There are severals methods for specifying source/target VMs in RPC policies.
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* `@tag:some-tag` - meaning a VM with tag `some-tag`
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* `@type:type` - meaning a VM of `type` (like `AppVM`, `TemplateVM` etc)
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- `@tag:some-tag` - meaning a VM with tag `some-tag`
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- `@type:type` - meaning a VM of `type` (like `AppVM`, `TemplateVM` etc)
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Target VM can be also specified as `@default`, which matches the case when calling VM didn't specified any particular target (either by using `@default` target, or empty target).
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For DisposableVMs, `@dispvm:DISP_VM` is very similar to `@dispvm` but forces using a particular VM (`DISP_VM`) as a base VM to be started as DisposableVM.
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For example:
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anon-whonix @dispvm:anon-whonix-dvm allow
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```
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anon-whonix @dispvm:anon-whonix-dvm allow
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```
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Adding such policy itself will not force usage of this particular `DISP_VM` - it will only allow it when specified by the caller.
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But `@dispvm:DISP_VM` can also be used as target in request redirection, so _it is possible_ to force particular `DISP_VM` usage, when caller didn't specify it:
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anon-whonix @dispvm allow,target=@dispvm:anon-whonix-dvm
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```
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anon-whonix @dispvm allow,target=@dispvm:anon-whonix-dvm
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```
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Note that without redirection, this rule would allow using default Disposable VM (`default_dispvm` VM property, which itself defaults to global `default_dispvm` property).
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Also note that the request will be allowed (`allow` action) even if there is no second rule allowing calls to `@dispvm:anon-whonix-dvm`, or even if there is a rule explicitly denying it.
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@ -150,9 +166,11 @@ It is not possible to select VM that policy would deny.
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By default no VM is selected, even if the caller provided some, but policy can specify default value using `default_target=` parameter.
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For example:
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work-mail work-archive allow
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work-mail @tag:work ask,default_target=work-files
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work-mail @default ask,default_target=work-files
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```
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work-mail work-archive allow
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work-mail @tag:work ask,default_target=work-files
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work-mail @default ask,default_target=work-files
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```
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The first rule allow call from `work-mail` to `work-archive`, without any confirmation.
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The second rule will ask the user about calls from `work-mail` VM to any VM with tag `work`.
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@ -196,15 +214,17 @@ And generally the less choices the user must make, the lower the chance to make
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The syntax is simple: when calling a service, add an argument to the service name separated with `+` sign, for example:
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$ qrexec-client-vm target_vm_name RPC_ACTION_NAME+ARGUMENT
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```
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$ qrexec-client-vm target_vm_name RPC_ACTION_NAME+ARGUMENT
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```
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Then create a policy as usual, including the argument (`/etc/qubes-rpc/policy/RPC_ACTION_NAME+ARGUMENT`).
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If the policy for the specific argument is not set (file does not exist), then the default policy for this service is loaded (`/etc/qubes-rpc/policy/RPC_ACTION_NAME`).
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In target VM (when the call is allowed) the service file will searched as:
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- `/etc/qubes-rpc/RPC_ACTION_NAME+ARGUMENT`
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- `/etc/qubes-rpc/RPC_ACTION_NAME`
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- `/etc/qubes-rpc/RPC_ACTION_NAME+ARGUMENT`
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- `/etc/qubes-rpc/RPC_ACTION_NAME`
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In any case, the script will receive `ARGUMENT` as its argument and additionally as `QREXEC_SERVICE_ARGUMENT` environment variable.
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This means it is also possible to install a different script for a particular service argument.
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@ -222,35 +242,45 @@ To demostrate some of the possibilities afforded by the qrexec framework, here a
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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").
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In someVM, create a file with the following contents and save it with the path `/usr/bin/our_test_add_client`:
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#!/bin/sh
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echo $1 $2 # pass data to RPC server
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exec cat >&$SAVED_FD_1 # print result to the original stdout, not to the other RPC endpoint
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```
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#!/bin/sh
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echo $1 $2 # pass data to RPC server
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exec cat >&$SAVED_FD_1 # print result to the original stdout, not to the other RPC endpoint
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```
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Our server will be anotherVM at `/usr/bin/our_test_add_server`.
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The code for this file is:
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#!/bin/sh
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read arg1 arg2 # read from stdin, which is received from the RPC client
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echo $(($arg1+$arg2)) # print to stdout, which is passed to the RPC client
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```
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#!/bin/sh
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read arg1 arg2 # read from stdin, which is received from the RPC client
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echo $(($arg1+$arg2)) # print to stdout, which is passed to the RPC client
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```
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We'll need to create a service called `test.Add` with its own definition and policy file in dom0.
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Now we need to define what the service does.
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In this case, it should call our addition script.
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We define the service with another one-line file, `/etc/qubes-rpc/test.Add`:
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/usr/bin/our_test_add_server
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```
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/usr/bin/our_test_add_server
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```
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The administrative domain will direct traffic based on the current RPC policies.
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In dom0, create a file at `/etc/qubes-rpc/policy/test.Add` containing the following:
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@anyvm @anyvm ask
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```
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@anyvm @anyvm ask
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```
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This will allow our client and server to communicate.
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Before we make the call, ensure that the client and server scripts have executable permissions.
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Finally, invoke the RPC service.
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$ qrexec-client-vm anotherVM test.Add /usr/bin/our_test_add_client 1 2
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```
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$ qrexec-client-vm anotherVM test.Add /usr/bin/our_test_add_client 1 2
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```
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We should get "3" as answer.
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(dom0 will ask for confirmation first.)
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@ -266,13 +296,15 @@ And no separate client script will be used.
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RPC server code (*/etc/qubes-rpc/test.File*)
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#!/bin/sh
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argument="$1" # service argument, also available as $QREXEC_SERVICE_ARGUMENT
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if [ -z "$argument" ]; then
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```
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#!/bin/sh
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argument="$1" # service argument, also available as $QREXEC_SERVICE_ARGUMENT
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if [ -z "$argument" ]; then
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echo "ERROR: No argument given!"
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exit 1
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fi
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cat "/home/user/rpc-file-storage/$argument"
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fi
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cat "/home/user/rpc-file-storage/$argument"
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```
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(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.)
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@ -286,12 +318,16 @@ We'll create three policy files in dom0:
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invoke RPC from `source_vm1` via
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/usr/lib/qubes/qrexec-client-vm target_vm test.File+testfile1
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```
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qrexec-client-vm target_vm test.File+testfile1
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```
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and we should get content of `/home/user/rpc-file-storage/testfile1` as answer.
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also possible to invoke RPC from `source_vm2` via
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/usr/lib/qubes/qrexec-client-vm target_vm test.File+testfile2
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```
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qrexec-client-vm target_vm test.File+testfile2
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```
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But when invoked with other argument or from different VM, it should be denied.
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