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, 3 insertions, 3 deletions

diff --git a/net/mac80211/ieee80211_sta.c b/net/mac80211/ieee80211_sta.c
index 8d620baba4fd..64476d9e8d77 100644
--- a/net/mac80211/ieee80211_sta.c
+++ b/net/mac80211/ieee80211_sta.c
@@ -1807,9 +1807,9 @@ static void ieee80211_rx_mgmt_assoc_resp(struct ieee80211_sub_if_data *sdata,
         if (!sta) {
                 struct ieee80211_sta_bss *bss;
                 sta = sta_info_add(local, dev, ifsta->bssid, GFP_KERNEL);
-                if (!sta) {
+                if (IS_ERR(sta)) {
                         printk(KERN_DEBUG "%s: failed to add STA entry for the"
-                               " AP\n", dev->name);
+                               " AP (error %ld)\n", dev->name, PTR_ERR(sta));
                         return;
                 }
                 bss = ieee80211_rx_bss_get(dev, ifsta->bssid,
@@ -3820,7 +3820,7 @@ struct sta_info * ieee80211_ibss_add_sta(struct net_device *dev,
                wiphy_name(local->hw.wiphy), print_mac(mac, addr), dev->name);
 
         sta = sta_info_add(local, dev, addr, GFP_ATOMIC);
-        if (!sta)
+        if (IS_ERR(sta))
                 return NULL;
 
         sta->flags |= WLAN_STA_AUTHORIZED;