Sending the FD over D-bus

* Sending the FD over D-bus
@ 2019-04-09 19:47 Ratan Gupta
  2019-04-10  2:13 ` William Kennington
  2019-04-11  7:51 ` vishwa
  0 siblings, 2 replies; 10+ messages in thread
From: Ratan Gupta @ 2019-04-09 19:47 UTC (permalink / raw)
  To: Tanous, Ed, bradleyb, openbmc

[-- Attachment #1: Type: text/plain, Size: 1243 bytes --]

Hi All,

As Discussed in yesterday community call, I did some POC to send the 
unix FD object over the D-Bus.

BackGround: We are exploring the possibilities how to send the secrets 
from one process to other process,

a) If the IPC is D-bus

b) Calling process doesn't have the root permission to write the secrets 
in the configuration file.

One of the proposal came, Can the calling process  send the unix fd over 
the D-Bus instead of sending the actual password

and receiving process reads the data from the sent fd.?

There was a confusion if some other app can snoop the D-bus message and 
get the FD and read it.I tried to simulate the same

behavior in the POC but not sure whether it is correct or not.

This POC has two files which is attached with this mail.

Dbus-Service(dbus-service-fd-test.py):  Method(readFD) which takes the 
unix fd as parameter reads it and send the data back

Dbus-Client(dbus-client-fd-test.py): Writes dummy data in the file, then 
opens the file and send the fd over D-bus.

After sending the data over D-bus , I introduced a sleep of 15 sec so 
that I can try to open the same fd from other

process,I open the python shell and try to open the shared FD but 
couldn't open it.

Ratan

[-- Attachment #2: dbus-client-fd-test.py --]
[-- Type: text/x-python, Size: 993 bytes --]

import unittest
import time

import dbus
import dbus.service
import dbus.glib

class TestCase(unittest.TestCase):

    def setUp(self):
        # WRITE SOMETHING IN THE FILE AND
        # close it
        f = open("/tmp/fd-test", "w")
        f.write("Hello, World!")
        f.close();

    def testHelloService(self):
        bus = dbus.SessionBus()
        service = bus.get_object('test.readFDservice', '/test/readFDservice')
        method = service.get_dbus_method('readFD', 'test.readFDservice')
        # Have written the hello world in the fd-test file, open the file and
        # send the fd over D-bus.
        f = open('/tmp/fd-test')
        print ("fd = %d" % f.fileno())
        fds = {0:dbus.types.UnixFd(f)}
        r = method("Test", fds)
        time.sleep(60) #To invoke another prg to try to read the shared fd.
        f.close()

        print ("r = %s" % r)
        assert r == "Hello, World!" # we got the same string

if __name__ == '__main__':
    unittest.main()

[-- Attachment #3: dbus-service-fd-test.py --]
[-- Type: text/x-python, Size: 782 bytes --]

import os

import dbus
import dbus.service
import dbus.glib
import gobject

class ReadFDService(dbus.service.Object):

    def __init__(self):
        bus_name = dbus.service.BusName('test.readFDservice', bus = dbus.SessionBus())
        dbus.service.Object.__init__(self, bus_name, '/test/readFDservice')

    def listen(self):
        loop = gobject.MainLoop()
        loop.run()

    @dbus.service.method('test.readFDservice', in_signature="sa{uh}")
    def readFD(self, serviceName, fds):
        print ([type(param) for param in (serviceName, fds)]  )
        print ("serviceName: %s" % serviceName)
        print ("fd: %s" % fds)
        r = os.fdopen(fds[0].take()).read()
        return r

if __name__ == '__main__':

    myservice = ReadFDService()
    myservice.listen()

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