Cannot Sandbox App

[reinhard2]

Hey! I have a Problem Sandboxing an App of mine!

I wrote an Mqtt app that connects to an external Mqtt Broker via cellular connection. When setting sandboxed: false in the .adef file it works fine and without problems.

When setting sandboxed to true and rebuilding the App it cannot connect to the broker anymore. I tried adding the “requires” section in the .adef but there were no apparent files in the log that need to be added.
I also used sbhelper to build and trace the app, this added a bunch of different files but it still doesn’t work in Sandboxed mode.

I also tried using strace -f but get Could not exec ‘strace’. No such file or directory in the log

Any tips?

[jyijyi]

You can refer to this sample to see how to use sandbox with cellular data

legatoproject/legato-af

[reinhard2]

I had a look at the application you sent me and changed my App accordingly but i still can’t get it to work. I attached a version of the app with the same problem.Mqtt.rar (656.3 KB)

[jyijyi]

Can the sample work?

[reinhard2]

Ok after instaling the httpGet example i get the exact same problem. When Sandboxed i get “Cannot resolve Hostname”, but unsandboxed it works fine.
(I didn’t change anything in the sample app, except the sandbox state for testing)

[jyijyi]

It works for old fw of wp76, you might try some old fw for wp8548.

Sample application Httpget cannot be run on WP76 R13

It says DNS cannot resolve host name: Oct 29 02:00:56 | httpGet[9967]/httpGetComponent T=main | httpGet.c GetUrl() 78 | curl_easy_perform() failed: Couldn’t resolve host name Any idea on this? I remember this sample works on R9.

Also here says it works on wp77 R12:

HttpGet example via modem does not work on WP7702

[reinhard2]

Ok, but i have 0 interest in running it on an older Firmware.
Is there no way of knowing why exactly its working when unsandboxed and failing when sandboxed?

[jyijyi]

Is that you must use sandbox?

From the log, do you see SMACK issue like below?

Apr 15 15:21:34 swi-mdm9x28-wp user.info Legato:  INFO | httpGet[2472] | HTTP Get!
Apr 15 15:21:34 swi-mdm9x28-wp user.notice kernel: [  562.769934] audit: type=1400 audit(1586935294.631:9): lsm=SMACK fn=smack_inode_getattr action=denied subject="app.http_get_WP76" object="admin" requested=r pid=2472 comm="httpGet" path="pipe:[11977]" dev="pipefs" ino=11977
Apr 15 07:21:34 swi-mdm9x28-wp user.err Legato: =ERR= | httpGet[2472]/httpGetComponent T=main | httpGet.c GetUrl() 79 | curl_easy_perform() failed: Couldn't resolve host name

If so, you might need to change the /etc/resolv.conf
permission

Opening Files in Sandboxed App

I don’t see problem with WP76 R13. You can use my app attached. root@swi-mdm9x28-wp:/tmp# cd /tmp root@swi-mdm9x28-wp:/tmp# root@swi-mdm9x28-wp:/tmp# echo hello_everybody > hello.txt root@swi-mdm9x28-wp:/tmp# root@swi-mdm9x28-wp:/tmp# chmod o+w hello.txt root@swi-mdm9x28-wp:/tmp# root@swi-mdm9x28-wp:/tmp# xattr set ‘security.SMACK64’ ‘app.hello7rwx’ hello.txt root@swi-mdm9x28-wp:/tmp# root@swi-mdm9x28-wp:/tmp# xattr get hello.txt name=security.SMACK64; value=app.hello7rwx root@swi-md…

[reinhard2]

It is not 100% needed i just would prefer to use it.

I just get:
Dec 28 13:33:33 swi-mdm9x15 user.info Legato: INFO | httpGet[13236] | HTTP Get!
Dec 28 13:33:33 swi-mdm9x15 user.info Legato: INFO | httpGet[13236]/httpGetComponent T=main | httpGet.c _httpGetComponent_COMPONENT_INIT() 133 | Requesting connection…
Dec 28 13:33:33 swi-mdm9x15 user.info Legato: INFO | httpGet[13236]/httpGetComponent T=main | httpGet.c ConnectionStateHandler() 110 | Interface rmnet0 connected.
Dec 28 13:33:53 swi-mdm9x15 user.err Legato: =ERR= | httpGet[13236]/httpGetComponent T=main | httpGet.c GetUrl() 77 | curl_easy_perform() failed: Couldn’t resolve host name

[jyijyi]

Can you check the content of resolv.conf file inside the application folder?

[reinhard2]

I’ve got thes 2:

nameserver 213.33.99.70
nameserver 80.120.17.70

[jyijyi]

Where is this file path?

[reinhard2]

Oh sorry,

root@swi-mdm9x15:/legato/systems/current/appsWriteable/httpGet/etc# cat resolv.conf
nameserver 213.33.99.70
nameserver 80.120.17.70

[jyijyi]

Is it ok the type this in console?

curl https://httpbin.org/get

[reinhard2]

root@swi-mdm9x15:/legato/systems/current/appsWriteable/httpGet/etc# curl https://httpbin.org/get
curl: (6) Could not resolve host: httpbin.org

root@swi-mdm9x15:/legato/systems/current/appsWriteable/httpGet/etc# cm data connect
Setting up profile 1
Connecting … ok
Checking if device ‘rmnet0’ is up … ok
Routing inet … ok
Updating /etc/resolv.conf … ok
Updating /etc/resolv.conf … ok
Testing connection … ^C
root@swi-mdm9x15:/legato/systems/current/appsWriteable/httpGet/etc# curl https://httpbin.org/get
{
“args”: {},
“headers”: {
“Accept”: “/”,
“Host”: “httpbin.org”,
“User-Agent”: “curl/7.58.0”,
“X-Amzn-Trace-Id”: “Root=1-5fe9ef99-1e3f8fe037955ec03e8ca987”
},
“origin”: “80.75.32.63”,
“url”: “https://httpbin.org/get”
}

[jyijyi]

How about using real ip address inside the .c file?

[reinhard2]

using the real IP adress i am able to get a proper response with httpGet

[jyijyi]

Is it ok for you?

You can try other api to get ip address

C Program to display hostname and IP address - GeeksforGeeks

[reinhard2]

Might try that, thanks!

[jyijyi]

Another method is using dns query by udp socket

DNS Query Code in C with Linux sockets