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>
diff --git a/net/mac80211/sta_info.c b/net/mac80211/sta_info.c
index b31a627..c6c0df4 100644
--- a/net/mac80211/sta_info.c
+++ b/net/mac80211/sta_info.c
@@ -55,19 +55,29 @@
return -ENOENT;
}
+/* must hold local->sta_lock */
+static struct sta_info *__sta_info_find(struct ieee80211_local *local,
+ u8 *addr)
+{
+ struct sta_info *sta;
+
+ sta = local->sta_hash[STA_HASH(addr)];
+ while (sta) {
+ if (compare_ether_addr(sta->addr, addr) == 0)
+ break;
+ sta = sta->hnext;
+ }
+ return sta;
+}
+
struct sta_info *sta_info_get(struct ieee80211_local *local, u8 *addr)
{
struct sta_info *sta;
read_lock_bh(&local->sta_lock);
- sta = local->sta_hash[STA_HASH(addr)];
- while (sta) {
- if (memcmp(sta->addr, addr, ETH_ALEN) == 0) {
- __sta_info_get(sta);
- break;
- }
- sta = sta->hnext;
- }
+ sta = __sta_info_find(local, addr);
+ if (sta)
+ __sta_info_get(sta);
read_unlock_bh(&local->sta_lock);
return sta;
@@ -110,8 +120,8 @@
EXPORT_SYMBOL(sta_info_put);
-struct sta_info * sta_info_add(struct ieee80211_local *local,
- struct net_device *dev, u8 *addr, gfp_t gfp)
+struct sta_info *sta_info_add(struct ieee80211_local *local,
+ struct net_device *dev, u8 *addr, gfp_t gfp)
{
struct sta_info *sta;
int i;
@@ -119,7 +129,7 @@
sta = kzalloc(sizeof(*sta), gfp);
if (!sta)
- return NULL;
+ return ERR_PTR(-ENOMEM);
kref_init(&sta->kref);
@@ -128,7 +138,7 @@
if (!sta->rate_ctrl_priv) {
rate_control_put(sta->rate_ctrl);
kfree(sta);
- return NULL;
+ return ERR_PTR(-ENOMEM);
}
memcpy(sta->addr, addr, ETH_ALEN);
@@ -158,9 +168,15 @@
}
skb_queue_head_init(&sta->ps_tx_buf);
skb_queue_head_init(&sta->tx_filtered);
- __sta_info_get(sta); /* sta used by caller, decremented by
- * sta_info_put() */
write_lock_bh(&local->sta_lock);
+ /* mark sta as used (by caller) */
+ __sta_info_get(sta);
+ /* check if STA exists already */
+ if (__sta_info_find(local, addr)) {
+ write_unlock_bh(&local->sta_lock);
+ sta_info_put(sta);
+ return ERR_PTR(-EEXIST);
+ }
list_add(&sta->list, &local->sta_list);
local->num_sta++;
sta_info_hash_add(local, sta);