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, 2 deletions

diff --git a/net/mac80211/ieee80211.c b/net/mac80211/ieee80211.c
index a00858dbab18..f82ebdd53d48 100644
--- a/net/mac80211/ieee80211.c
+++ b/net/mac80211/ieee80211.c
@@ -838,8 +838,8 @@ int ieee80211_if_update_wds(struct net_device *dev, u8 *remote_addr)
 
         /* Create STA entry for the new peer */
         sta = sta_info_add(local, dev, remote_addr, GFP_KERNEL);
-        if (!sta)
-                return -ENOMEM;
+        if (IS_ERR(sta))
+                return PTR_ERR(sta);
 
         sta->flags |= WLAN_STA_AUTHORIZED;