Dan Williams wrote:
> <hidden> this is something that ieee80211 does that's completely wrong.
Because it is not a part of the 802.11 specification, AP vendors have
each implemented their own method for disguising the SSID. Some set the
length to the actual SSID length but put fill the SSID with '\0', some
set the length and SSID to a single space, some set the length to 0.
Since the scan results are supposed to report networks found; the first
agreement we need to make between user space and the kernel is how we
define a 'network', and how do we determine when a network has been
updated?
Take the following flow where you have an AP that supports two networks
on the same channel using the same MAC, but does not beacon a hidden
network if a non-hidden network also exists:
Indirect scan finds via probe request:
ssid_len=3, ssid=Foo, channel 1, BSSID: 00:0e:de:ad:be:ef
and via beacons:
ssid_len=3, ssid=Foo, channel 1, BSSID: 00:0e:de:ad:be:ef
The user configures the SSID to look for to be Bar.
A direct scan for 'Bar' is sent, and the following is found via probe
request:
ssid_len=3, ssid=Bar, channel 1, BSSID: 00:0e:de:ad:be:ef
and via beacons:
ssid_len=3, ssid=Foo, channel 1, BSSID: 00:0e:de:ad:be:ef
The network Bar is associated with, and time passes with no data or
probe requests being sent (idle network). Beacons are received for Foo,
but nothing for Bar (since the AP isn't beaconing hidden networks).
Now you look for scan results with an indirect scan, and you will only see:
ssid_len=3, ssid=Foo, channel 1, BSSID: 00:0e:de:ad:be:ef
Aside from the probe response for Bar, there are never any beacons that
indicate that the network Bar still exists. Scan results *should*
display Foo and Bar, but the current ieee80211 subsystem will filter out
Bar once 15s has passed without receiving a probe response.
Currently ieee80211 does not differentiate between probe responses and
beacons for collecting network data. To "fix" the problem we have now,
ieee80211 needs to be changed to be able to distinguish between probe
respones and beacons, and update all networks that match channel and MAC
when a beacon is received (regardless of SSID) and update a specific
network if the frame is a probe response.
If the above change is made, we can perhaps remove all knowledge of a
hidden vs. broadcast network from the drivers and ieee80211 subsystem.
> Drivers need to report the _exact_ ESSID from the air in their scan
> results. It's up to the user space app to deal with ESSID length of 0.
Agree the kernel should pass the SSID as received.
Ideally user space should just register to receive all beacons and probe
responses from the network device and do all the parsing and network
management, with a timing interval specified for frequency to receive
beacons/probe responses that have not changed (although one packet every
100ms isn't likely to cause too much thrash)
Exporting the entire frame allows user space to provide information on
802.11h, 802.11e, 802.11i and other network capabilities that currently
aren't exposed via the wireless extension interface.
Doing this also has the advantage of being able to remove all scan and
network collection logistics out of the kernel and into user space.
In light of the above, I started playing with a raw packet interface on
the ipw2200 and ipw3945 projects that export all frames to user space in
radiotap format through a 2nd network device. I am working on changing
the way the raw packet interface is configured to be via netlink (vs. a
sysfs entry) but you can apply it to ipw2200-1.1.1 via
http://ipw2200.sf.net/ipw2200-1.1.1-rtap_iface.patch if interested.
> Signed-off-by: Dan Williams <[EMAIL PROTECTED]>
>
> --- net/ieee80211/ieee80211_wx.c 2006-03-24 10:43:04.000000000 -0500
> +++ net/ieee80211/ieee80211_wx.c 2006-03-24 10:53:27.000000000 -0500
> @@ -64,8 +64,8 @@
> iwe.cmd = SIOCGIWESSID;
> iwe.u.data.flags = 1;
> if (network->flags & NETWORK_EMPTY_ESSID) {
> - iwe.u.data.length = sizeof("<hidden>");
> - start = iwe_stream_add_point(start, stop, &iwe, "<hidden>");
> + iwe.u.data.length = 0;
> + start = iwe_stream_add_point(start, stop, &iwe, "");
> } else {
> iwe.u.data.length = min(network->ssid_len, (u8) 32);
> start = iwe_stream_add_point(start, stop, &iwe, network->ssid);
See (untested) attached to change ieee80211 to expose the SSID as received.
James
ieee80211: Change _rx and _wx to export full SSIDs as received over air
This patch modifies the frame parsing code to copy the contents of a
"hidden" network's SSID information element as well as modify the
wireless extension handler for providing that information to user space.
With this patch applied, no "<hidden>" network string will be returned
to user space -- it is up to user space to determine if a network is
hidden or not.
Signed-off-by: James Ketrenos <[EMAIL PROTECTED]>
---
ieee80211/ieee80211_rx.c | 4 +---
ieee80211/ieee80211_wx.c | 11 +++--------
2 files changed, 4 insertions(+), 11 deletions(-)
--- a/net/ieee80211/ieee80211_rx.c 2006-03-24 10:50:00.000000000 -0600
+++ b/net/ieee80211/ieee80211_rx.c 2006-03-24 10:50:23.000000000 -0600
@@ -1000,10 +1000,8 @@ static int ieee80211_parse_info_param(st
switch (info_element->id) {
case MFIE_TYPE_SSID:
if (ieee80211_is_empty_essid(info_element->data,
- info_element->len)) {
+ info_element->len))
network->flags |= NETWORK_EMPTY_ESSID;
- break;
- }
network->ssid_len = min(info_element->len,
(u8) IW_ESSID_MAX_SIZE);
--- a/net/ieee80211/ieee80211_wx.c 2006-03-24 10:50:06.000000000 -0600
+++ a/net/ieee80211/ieee80211_wx.c 2006-03-24 10:50:54.000000000 -0600
@@ -63,14 +63,9 @@ static char *ipw2100_translate_scan(stru
/* Add the ESSID */
iwe.cmd = SIOCGIWESSID;
iwe.u.data.flags = 1;
- if (network->flags & NETWORK_EMPTY_ESSID) {
- iwe.u.data.length = sizeof("<hidden>");
- start = iwe_stream_add_point(start, stop, &iwe, "<hidden>");
- } else {
- iwe.u.data.length = min(network->ssid_len, (u8) 32);
- start = iwe_stream_add_point(start, stop, &iwe, network->ssid);
- }
-
+ iwe.u.data.length = min(network->ssid_len, (u8) 32);
+ start = iwe_stream_add_point(start, stop, &iwe, network->ssid);
+
/* Add the protocol name */
iwe.cmd = SIOCGIWNAME;
snprintf(iwe.u.name, IFNAMSIZ, "IEEE 802.11%s",
