mac80211: atomically check whether STA exists already

When a STA structure is added, it is often checked whether it
already exists before adding it. This, however, isn't done
atomically so there is a race condition that could lead to two
STA structures being added with the same MAC address. This
patch changes sta_info_add() to return an ERR_PTR in case
of failure and adds the failure mode -EEXIST when the STA
already exists.

Signed-off-by: Johannes Berg <johannes@sipsolutions.net>
Cc: Luis Carlos Cobo <luisca@cozybit.com>
Signed-off-by: John W. Linville <linville@tuxdriver.com>

1 files changed, 2 insertions, 9 deletions

diff --git a/net/mac80211/cfg.c b/net/mac80211/cfg.c
index a083cc78855e..b0c41a0cee79 100644
--- a/net/mac80211/cfg.c
+++ b/net/mac80211/cfg.c
@@ -562,13 +562,6 @@ static int ieee80211_add_station(struct wiphy *wiphy, struct net_device *dev,
         if (!netif_running(dev))
                 return -ENETDOWN;
 
-        /* XXX: get sta belonging to dev */
-        sta = sta_info_get(local, mac);
-        if (sta) {
-                sta_info_put(sta);
-                return -EEXIST;
-        }
-
         if (params->vlan) {
                 sdata = IEEE80211_DEV_TO_SUB_IF(params->vlan);
 
@@ -579,8 +572,8 @@ static int ieee80211_add_station(struct wiphy *wiphy, struct net_device *dev,
                 sdata = IEEE80211_DEV_TO_SUB_IF(dev);
 
         sta = sta_info_add(local, dev, mac, GFP_KERNEL);
-        if (!sta)
-                return -ENOMEM;
+        if (IS_ERR(sta))
+                return PTR_ERR(sta);
 
         sta->dev = sdata->dev;
         if (sdata->vif.type == IEEE80211_IF_TYPE_VLAN ||