mac80211: fix racy usage of chanctx->refcount
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 <michal.kazior@tieto.com> Signed-off-by: Johannes Berg <johannes.berg@intel.com>
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@ -3225,7 +3225,7 @@ int ieee80211_channel_switch(struct wiphy *wiphy, struct net_device *dev,
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{
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struct ieee80211_sub_if_data *sdata = IEEE80211_DEV_TO_SUB_IF(dev);
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struct ieee80211_local *local = sdata->local;
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struct ieee80211_chanctx_conf *chanctx_conf;
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struct ieee80211_chanctx_conf *conf;
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struct ieee80211_chanctx *chanctx;
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int err, num_chanctx, changed = 0;
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@ -3241,23 +3241,24 @@ int ieee80211_channel_switch(struct wiphy *wiphy, struct net_device *dev,
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&sdata->vif.bss_conf.chandef))
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return -EINVAL;
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rcu_read_lock();
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chanctx_conf = rcu_dereference(sdata->vif.chanctx_conf);
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if (!chanctx_conf) {
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rcu_read_unlock();
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mutex_lock(&local->chanctx_mtx);
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conf = rcu_dereference_protected(sdata->vif.chanctx_conf,
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lockdep_is_held(&local->chanctx_mtx));
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if (!conf) {
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mutex_unlock(&local->chanctx_mtx);
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return -EBUSY;
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}
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/* don't handle for multi-VIF cases */
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chanctx = container_of(chanctx_conf, struct ieee80211_chanctx, conf);
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chanctx = container_of(conf, struct ieee80211_chanctx, conf);
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if (chanctx->refcount > 1) {
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rcu_read_unlock();
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mutex_unlock(&local->chanctx_mtx);
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return -EBUSY;
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}
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num_chanctx = 0;
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list_for_each_entry_rcu(chanctx, &local->chanctx_list, list)
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num_chanctx++;
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rcu_read_unlock();
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mutex_unlock(&local->chanctx_mtx);
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if (num_chanctx > 1)
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return -EBUSY;
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