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mac80211: fix racy usage of chanctx->refcount

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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>
This commit is contained in:
Michal Kazior 2014-04-09 15:29:32 +02:00 committed by Johannes Berg
parent 1f0d54cdcf
commit 2b32713d72
1 changed files with 9 additions and 8 deletions
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17
net/mac80211/cfg.c
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@ -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;