From mboxrd@z Thu Jan 1 00:00:00 1970 Return-path: Received: from s3.sipsolutions.net ([5.9.151.49]:35419 "EHLO sipsolutions.net" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1750996AbbAWJm6 (ORCPT ); Fri, 23 Jan 2015 04:42:58 -0500 Message-ID: <1422006174.2728.12.camel@sipsolutions.net> (sfid-20150123_104302_972030_ACE35486) Subject: Re: [PATCH v3] mac80211: Avoid STA expiration timer truncation to u32 From: Johannes Berg To: Masashi Honma Cc: linux-wireless@vger.kernel.org, me@bobcopeland.com Date: Fri, 23 Jan 2015 10:42:54 +0100 In-Reply-To: <1421722023-4691-1-git-send-email-masashi.honma@gmail.com> (sfid-20150120_034734_203758_428E04AE) References: <1421722023-4691-1-git-send-email-masashi.honma@gmail.com> (sfid-20150120_034734_203758_428E04AE) Content-Type: text/plain; charset="UTF-8" Mime-Version: 1.0 Sender: linux-wireless-owner@vger.kernel.org List-ID: On Tue, 2015-01-20 at 11:47 +0900, Masashi Honma wrote: > On some combination of plink_timeout and HZ, the STA expiration timer will be > unexpectedly truncated to u32. Maybe there is a question "Who sets such a large > number to plink_timeout ?". At least wpa_supplicant will set 0xffffffff to > plink_timeout to disable this timer because wpa_supplicant has it's own > expiration mechanism. Ok - but that doesn't really disable the timer? Perhaps we should have a new userspace API to explicitly disable it? OTOH, worst case I guess that means it's like >100 years in the future, so I guess it doesn't matter. However, though, you can hardly rely on this fix being present in the kernel, so you can't really set such a large value unconditionally anyway, no? Otherwise a newer wpa_supplicant running on an older kernel would suddenly behave incorrectly. That doesn't seem right. Having an explicit feature to disable plink timeout would perhaps be better? > --- a/net/mac80211/mesh.c > +++ b/net/mac80211/mesh.c > @@ -573,8 +573,11 @@ static void ieee80211_mesh_housekeeping(struct ieee80211_sub_if_data *sdata) > { > struct ieee80211_if_mesh *ifmsh = &sdata->u.mesh; > u32 changed; > + u64 exp_time; > > - ieee80211_sta_expire(sdata, ifmsh->mshcfg.plink_timeout * HZ); > + exp_time = ifmsh->mshcfg.plink_timeout * (u64)HZ; > + if (exp_time < 0x100000000) > + ieee80211_sta_expire(sdata, exp_time); I'm not convinced this is right. For one, I believe on 32-bit machines you'll need to write "0x100000000ULL" instead of the plain constant. Perhaps preferably, you'd use use ">= MAX_UINT". However, the argument to ieee80211_sta_expire() is an unsigned long (as is jiffies), so on 64-bit machines you could even still use the value and the conditional isn't needed. Given these complications, I would prefer having a feature attribute to treat e.g. 0 as disabling the timer entirely, and if this feature isn't present then have wpa_supplicant instead use a safe value that doesn't trigger the kernel bug - e.g. 0xffffffff/1000 [which is the max possible HZ]. johannes