Return-path: Received: from mail-vx0-f174.google.com ([209.85.220.174]:57396 "EHLO mail-vx0-f174.google.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1751131Ab2D3HaY convert rfc822-to-8bit (ORCPT ); Mon, 30 Apr 2012 03:30:24 -0400 Received: by vcqp1 with SMTP id p1so1849508vcq.19 for ; Mon, 30 Apr 2012 00:30:23 -0700 (PDT) MIME-Version: 1.0 In-Reply-To: References: Date: Mon, 30 Apr 2012 13:00:23 +0530 Message-ID: (sfid-20120430_093031_339287_4051228B) Subject: Re: bss table corruption From: Mohammed Shafi To: Emmanuel Grumbach Cc: linux-wireless , Johannes Berg Content-Type: text/plain; charset=ISO-8859-1 Sender: linux-wireless-owner@vger.kernel.org List-ID: Hi Emmanuel, On Mon, Apr 30, 2012 at 10:58 AM, Emmanuel Grumbach wrote: > For quite a while now (not sure I can tell exactly for how long) we > see issues in association and scan list. > We send probe before authentication, get the probe response but never > send the authentication. > Moreover a lot of entries in the BSS list are duplicated. > > I began to look at it and ended up to understand that these 2 issues > are related: we just can't find an existing BSS in the BSS table. > Obviously this causes the second issue. The reason was it breaks the > association is that ieee80211_probe_auth will never be able to find > the IEs of the probe response since we couldn't fetch the BSS when we > parsed the probe response. In short: > > ? ? ? ?if (auth_data->bss->proberesp_ies) { > always return false.... and we fall back to send yet another probe request. > > As you probably know, the BSS table is implemented with an Red Black > Tree which requires its elements to be comparable. The compare > function compares the BSSID which is not always unique (there can be > several SSIDs on the same BSSID), so all the IEs are also compared. > But is this a good idea ? > It seems that since the IEs of an BSS may change from time to time > this compare function is not consistent... > > Just for playing I always return a positive value in cmp_bss (to have > all the nodes serialized and avoid the possibility to miss a existing > node) and don't rebalance the tree after insertion... the bug > disappeared. > > Thought ? > > Emmanuel Grumbach > egrumbach@gmail.com > -- > To unsubscribe from this list: send the line "unsubscribe linux-wireless" in > the body of a message to majordomo@vger.kernel.org > More majordomo info at ?http://vger.kernel.org/majordomo-info.html we are comparing the BSSID of the new entry with the old entry (ie) we would return positive (with your latest fix) if the BSSID of the new entry > BSSID of the old entry, should not we do the same for comparing frequency, ie length and ie content. just got a doubt if this is by design we have things like this. net/wireless/scan.c | 6 +++--- 1 files changed, 3 insertions(+), 3 deletions(-) diff --git a/net/wireless/scan.c b/net/wireless/scan.c index 70faadf..fda4eef 100644 --- a/net/wireless/scan.c +++ b/net/wireless/scan.c @@ -271,7 +271,7 @@ static int cmp_ies(u8 num, u8 *ies1, size_t len1, u8 *ies2, size_t len2) /* sort by length first, then by contents */ if (ie1[1] != ie2[1]) - return ie2[1] - ie1[1]; + return ie1[1] - ie2[1]; return memcmp(ie1 + 2, ie2 + 2, ie1[1]); } @@ -361,7 +361,7 @@ static int cmp_bss_core(struct cfg80211_bss *a, int r; if (a->channel != b->channel) - return b->channel->center_freq - a->channel->center_freq; + return a->channel->center_freq - b->channel->center_freq; if (is_mesh_bss(a)&& is_mesh_bss(b)) { r = cmp_ies(WLAN_EID_MESH_ID, @@ -433,7 +433,7 @@ static int cmp_hidden_bss(struct cfg80211_bss *a, /* sort by length first, then by contents */ if (ie1[1] != ie2[1]) - return ie2[1] - ie1[1]; + return ie1[1] - ie2[1]; /* zeroed SSID ie is another indication of a hidden bss */ for (i = 0; i< ie2[1]; i++) -- thanks, shafi