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@xxxxxxxxx>
---
v2:
* use rcu_dereference_protected()
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 64e152d..328c9a3 100644
--- a/net/mac80211/cfg.c
+++ b/net/mac80211/cfg.c
@@ -3282,7 +3282,7 @@ 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;
@@ -3299,23 +3299,24 @@ 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
--
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