Return-path: Received: from mail-ee0-f47.google.com ([74.125.83.47]:46809 "EHLO mail-ee0-f47.google.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1754680AbaCRN7V (ORCPT ); Tue, 18 Mar 2014 09:59:21 -0400 Received: by mail-ee0-f47.google.com with SMTP id b15so5417747eek.34 for ; Tue, 18 Mar 2014 06:59:20 -0700 (PDT) From: Michal Kazior To: linux-wireless@vger.kernel.org Cc: johannes@sipsolutions.net, Michal Kazior Subject: [RFC 11/21] mac80211: fix racy usage of chanctx->refcount Date: Tue, 18 Mar 2014 14:53:14 +0100 Message-Id: <1395150804-24090-12-git-send-email-michal.kazior@tieto.com> (sfid-20140318_145938_007831_D3FBBA3D) In-Reply-To: <1395150804-24090-1-git-send-email-michal.kazior@tieto.com> References: <1395150804-24090-1-git-send-email-michal.kazior@tieto.com> Sender: linux-wireless-owner@vger.kernel.org List-ID: Channel context refcount is protected by chanctx_mtx. Accessing the value without holding the mutex is racy. RCU section didn't guarantee anything here. Theoretically ieee80211_channel_switch() could fail to see refcount change and read "1" instead of, e.g. "2". This means mac80211 could accept CSA even though it shouldn't have. Signed-off-by: Michal Kazior --- net/mac80211/cfg.c | 17 +++++++++-------- 1 file changed, 9 insertions(+), 8 deletions(-) diff --git a/net/mac80211/cfg.c b/net/mac80211/cfg.c index 137d379..61b62f4 100644 --- a/net/mac80211/cfg.c +++ b/net/mac80211/cfg.c @@ -3225,7 +3225,7 @@ int ieee80211_channel_switch(struct wiphy *wiphy, struct net_device *dev, { struct ieee80211_sub_if_data *sdata = IEEE80211_DEV_TO_SUB_IF(dev); struct ieee80211_local *local = sdata->local; - struct ieee80211_chanctx_conf *chanctx_conf; + struct ieee80211_chanctx_conf *conf; struct ieee80211_chanctx *chanctx; int err, num_chanctx, changed = 0; @@ -3241,23 +3241,24 @@ int ieee80211_channel_switch(struct wiphy *wiphy, struct net_device *dev, &sdata->vif.bss_conf.chandef)) return -EINVAL; - rcu_read_lock(); - chanctx_conf = rcu_dereference(sdata->vif.chanctx_conf); - if (!chanctx_conf) { - rcu_read_unlock(); + mutex_lock(&local->chanctx_mtx); + conf = rcu_dereference_protected(sdata->vif.chanctx_conf, + lockdep_is_held(&local->chanctx_mtx)); + if (!conf) { + mutex_unlock(&local->chanctx_mtx); return -EBUSY; } /* don't handle for multi-VIF cases */ - chanctx = container_of(chanctx_conf, struct ieee80211_chanctx, conf); + chanctx = container_of(conf, struct ieee80211_chanctx, conf); if (chanctx->refcount > 1) { - rcu_read_unlock(); + mutex_unlock(&local->chanctx_mtx); return -EBUSY; } num_chanctx = 0; list_for_each_entry_rcu(chanctx, &local->chanctx_list, list) num_chanctx++; - rcu_read_unlock(); + mutex_unlock(&local->chanctx_mtx); if (num_chanctx > 1) return -EBUSY; -- 1.8.5.3