Return-path: Received: from mail-we0-f174.google.com ([74.125.82.174]:43988 "EHLO mail-we0-f174.google.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1751559Ab2D3HhP convert rfc822-to-8bit (ORCPT ); Mon, 30 Apr 2012 03:37:15 -0400 Received: by wejx9 with SMTP id x9so1636696wej.19 for ; Mon, 30 Apr 2012 00:37:13 -0700 (PDT) MIME-Version: 1.0 In-Reply-To: References: Date: Mon, 30 Apr 2012 10:37:13 +0300 Message-ID: (sfid-20120430_093720_017260_B868C731) Subject: Re: bss table corruption From: Emmanuel Grumbach To: Mohammed Shafi Cc: linux-wireless , Johannes Berg Content-Type: text/plain; charset=ISO-8859-1 Sender: linux-wireless-owner@vger.kernel.org List-ID: On Mon, Apr 30, 2012 at 10:30, Mohammed Shafi wrote: > 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. > > Frankly I didn't think about this :-), but I think the current behavior is correct even if it is not intuitive. All we need a consistent comparison operator. But I don't mind folding you suggestion retest and resubmit. > 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