From mboxrd@z Thu Jan 1 00:00:00 1970 Return-path: Received: from remail2.raritan.com ([62.132.199.138]:45914 "EHLO remail2.raritan.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S932085Ab2B1O3r (ORCPT ); Tue, 28 Feb 2012 09:29:47 -0500 Message-ID: <4F4CE4D6.6020108@raritan.com> (sfid-20120228_152950_864254_C21F9143) Date: Tue, 28 Feb 2012 15:29:42 +0100 From: Ronald Wahl MIME-Version: 1.0 To: linux-wireless@vger.kernel.org Subject: Occasional truncated scan results Content-Type: text/plain; charset=UTF-8; format=flowed Sender: linux-wireless-owner@vger.kernel.org List-ID: Hi, some time ago I had an issue with a wireless device that it couldn't associate to the AP over some time. I found out that the BSS with the corresponding SSID was the last in the scan list and was truncated - all the IEs were missing and so the supplicant did not detect that it supports WPA2 and hence ignored it. After some playing with different wireless devices I discovered that this is not limited to specific drivers so I digged a bit in the scan code in net/wireless/scan.c and found the culprit: The scan result is put together with the iwe_stream_* functions that place data into a provided buffer if enough space is available in the buffer. Otherwise the functions do just nothing. Before a BSS is added there is a check if some minimum space is available but after the BSS has been added it is not clear how many data actually has been placed into the buffer. So especially (but not neccessarily only) the last BSS is prone to be incomplete. I my case all the IEs were missing and this was persistent over some time (the persitence behavior seems to differs between drivers - probably depends on how the scanning is implemented). Currently I implemented a heuristic that checks if some minimum space (currently 256 bytes) is still free _after_ adding a BSS and otherwise return -E2BIG so the user space can provide a larger buffer but this is a crappy hack. Can the code be changed in some way to more reliably detect if some data did not fit into the buffer and report this to user space? - ron -- Ronald Wahl - ronald.wahl@raritan.com - Phone +49 375271349-0 Fax -99 Raritan Deutschland GmbH, Kornmarkt 7, 08056 Zwickau, Germany USt-IdNr. DE813094160, Steuer-Nr. 227/117/01749 Amtsgericht Chemnitz HRB 23605 Geschäftsführung: Stuart Hopper, Burkhard Wessler