MozillaTeam/Specs/Karmic/FirefoxWifiScanning

FirefoxWifiScanning

Launchpad Entry: mozilla-karmic-firefox-wifi-scanning
Affected Packages: wpasupplicant, firefox-3.5+
Creator: Alexander Sack

please don't edit this spec without contacting the author or the approver first

Intro

Firefox 3.5 will ship a new feature that supports geolocation services based on wifi APs found during scans. This spec only covers system setups that use a dbus enabled wpasupplicant for their wifi connectivity (e.g. NetworkManager, connman, ifupdown). This spec has three parts:

suggest changes required to the wpasupplicant default dbus access policies to allow applications to leverage its scan results.
outline best practices for applications in general that need to access wifi scan results.
outline a patch for the mozilla code base to support wpasupplicant scan result instead of the current wireless extension approach

Use-Case

Application F (like Firefox 3.5) wants to provide geolocation based services to the user and needs recent wifi scan results to leverage a geolocation service provider (such as google).

Design

Problem: Using wireless extensions from unprivileged user-space programs to obtain scan result has deficiencies:

iwlist scan does not trigger a real scan
iwlist scan list results age and even get consumed by other apps; this will cause the scan result list to be regularly empty and unreliable.

Solution: use wpasupplicant to access a better AP cache.

Details: On wpasupplicant enabled systems you can (in theory) listen to wpasupplicant ScanResultsAvailable dbus signal and then get details using the appropriate wpasupplicant intefaces and members

It might also make sense to allow users at the console to trigger scans in wpasupplicant; this will prevent outdated lists for users that don't use a connection manager performing background scanning.

Implementation

changes to wpasupplicant dbus policy

grant access for default to

scanResults member of the fi.epitest.hostap.WPASupplicant.Interface interface
properties member of the fi.epitest.hostap.WPASupplicant.BSSID interface

Example dbus policy section to grant those privileges (based on current wpasupplicant policy):

<!DOCTYPE busconfig PUBLIC
 "-//freedesktop//DTD D-BUS Bus Configuration 1.0//EN"
 "http://www.freedesktop.org/standards/dbus/1.0/busconfig.dtd">
<busconfig>
        <policy user="root">
                <allow own="fi.epitest.hostap.WPASupplicant"/>

                <allow send_destination="fi.epitest.hostap.WPASupplicant"/>
                <allow send_interface="fi.epitest.hostap.WPASupplicant"/>
        </policy>
        <policy group="netdev">
                <allow send_destination="fi.epitest.hostap.WPASupplicant"/>
                <allow send_interface="fi.epitest.hostap.WPASupplicant"/>
        </policy>
        <policy context="default">
                <deny own="fi.epitest.hostap.WPASupplicant"/>
                <deny send_destination="fi.epitest.hostap.WPASupplicant"/>
                <deny send_interface="fi.epitest.hostap.WPASupplicant"/>

                <!-- extra privileges to access scan result details for unprivileged users -->
                <allow send_interface="fi.epitest.hostap.WPASupplicant.Interface"
                       send_member="scanResults"/>
                <allow send_interface="fi.epitest.hostap.WPASupplicant.BSSID"
                       send_member="properties"/>
        </policy>
</busconfig>

same as above, but just the diff -u:

--- /etc/dbus-1/system.d/wpa_supplicant.conf.orig       2009-06-16 16:01:39.000000000 +0200
+++ /etc/dbus-1/system.d/wpa_supplicant.conf    2009-06-16 16:03:32.000000000 +0200
@@ -16,5 +16,9 @@
                 <deny own="fi.epitest.hostap.WPASupplicant"/>
                 <deny send_destination="fi.epitest.hostap.WPASupplicant"/>
                 <deny send_interface="fi.epitest.hostap.WPASupplicant"/>
+                <allow send_interface="fi.epitest.hostap.WPASupplicant.Interface"
+                       send_member="scanResults"/>
+                <allow send_interface="fi.epitest.hostap.WPASupplicant.BSSID"
+                       send_member="properties"/>
         </policy>
 </busconfig>

Best practices for tracking wpasupplicant scan results

listen to scanResults; the dbus signal that matters is

signal sender=:1.8 -> dest=(null destination) serial=11608 path=/fi/epitest/hostap/WPASupplicant/Interfaces/6; interface=fi.epitest.hostap.WPASupplicant.Interface; member=ScanResultsAvailable

to obtain current list of scanResults call the dbus scanResults member method

$ dbus-send --print-reply --dest="fi.epitest.hostap.WPASupplicant" --system "/fi/epitest/hostap/WPASupplicant/Interfaces/6" "fi.epitest.hostap.WPASupplicant.Interface.scanResults"
method return sender=:1.8 -> dest=:1.643 reply_serial=2
   array [
      object path "/fi/epitest/hostap/WPASupplicant/Interfaces/6/BSSIDs/00227532243f"
      object path "/fi/epitest/hostap/WPASupplicant/Interfaces/6/BSSIDs/0012bfdea08e"
      object path "/fi/epitest/hostap/WPASupplicant/Interfaces/6/BSSIDs/0012bf7a07c9"
      object path "/fi/epitest/hostap/WPASupplicant/Interfaces/6/BSSIDs/00150c53e790"
      object path "/fi/epitest/hostap/WPASupplicant/Interfaces/6/BSSIDs/00184d19b334"
      object path "/fi/epitest/hostap/WPASupplicant/Interfaces/6/BSSIDs/00146c43ca4a"
      object path "/fi/epitest/hostap/WPASupplicant/Interfaces/6/BSSIDs/00230801d407"
      object path "/fi/epitest/hostap/WPASupplicant/Interfaces/6/BSSIDs/0013494e13c1"
      object path "/fi/epitest/hostap/WPASupplicant/Interfaces/6/BSSIDs/001d19b62e15"
      object path "/fi/epitest/hostap/WPASupplicant/Interfaces/6/BSSIDs/001b2fe8e05e"
      object path "/fi/epitest/hostap/WPASupplicant/Interfaces/6/BSSIDs/001b119cec36"
      object path "/fi/epitest/hostap/WPASupplicant/Interfaces/6/BSSIDs/000124f4831c"
   ]

to obtain details for each scan result, use:

dbus-send --print-reply --dest="fi.epitest.hostap.WPASupplicant" --system "/fi/epitest/hostap/WPASupplicant/Interfaces/6/BSSIDs/0012bfdea08e" "fi.epitest.hostap.WPASupplicant.BSSID.properties"
... (result)

Firefox changes

Firefox implementation nsWifiScannerUnix.cpp should provide xpcom hook to plug in toolkit/unix shipped scanners; unix scanner should fallback to current iw implementation if the toolkit/unix scanner fails.

toolkit/unix scanner needs to listen to ScanResultsAvailable signals on the dbus. From those signals it can track active interfaces and query those for scanResults.

Main action on firefox from this spec is filing an upstream bug and working together with upstream. Once there is a trunk fix, consider to backport for 1.9.1 branch and consider to initiate major change request.

Comments

MozillaTeam/Specs/Karmic/FirefoxWifiScanning (last edited 2009-06-16 14:05:31 by g225201237)

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