mac80211: split ieee80211_key_alloc/free

In order to RCU-ify sta_info, we need to be able to allocate
a key without linking it to an sdata/sta structure (because
allocation cannot be done in an rcu critical section). This
patch splits up ieee80211_key_alloc() and updates all users
appropriately.

While at it, this patch fixes a number of race conditions
such as finally making key replacement atomic, unfortunately
at the expense of more complex code.

Note that this patch documents /existing/ bugs with sta info
and key interaction, there is currently a race condition
when a sta info is freed without holding the RTNL. This will
finally be fixed by a followup patch.

Signed-off-by: Johannes Berg <johannes@sipsolutions.net>
Signed-off-by: John W. Linville <linville@tuxdriver.com>

net/mac80211/cfg.c

@@ -123,6 +123,7 @@ static int ieee80211_add_key(struct wiphy *wiphy, struct net_device *dev,
 	struct sta_info *sta = NULL;
 	enum ieee80211_key_alg alg;
 	int ret;
+	struct ieee80211_key *key;
 
 	sdata = IEEE80211_DEV_TO_SUB_IF(dev);
 
@@ -141,16 +142,21 @@ static int ieee80211_add_key(struct wiphy *wiphy, struct net_device *dev,
 		return -EINVAL;
 	}
 
+	key = ieee80211_key_alloc(alg, key_idx, params->key_len, params->key);
+	if (!key)
+		return -ENOMEM;
+
 	if (mac_addr) {
 		sta = sta_info_get(sdata->local, mac_addr);
-		if (!sta)
+		if (!sta) {
+			ieee80211_key_free(key);
 			return -ENOENT;
+		}
 	}
 
+	ieee80211_key_link(key, sdata, sta);
+
 	ret = 0;
-	if (!ieee80211_key_alloc(sdata, sta, alg, key_idx,
-				 params->key_len, params->key))
-		ret = -ENOMEM;
 
 	if (sta)
 		sta_info_put(sta);
@@ -164,6 +170,7 @@ static int ieee80211_del_key(struct wiphy *wiphy, struct net_device *dev,
 	struct ieee80211_sub_if_data *sdata;
 	struct sta_info *sta;
 	int ret;
+	struct ieee80211_key *key;
 
 	sdata = IEEE80211_DEV_TO_SUB_IF(dev);
 
@@ -173,9 +180,11 @@ static int ieee80211_del_key(struct wiphy *wiphy, struct net_device *dev,
 			return -ENOENT;
 
 		ret = 0;
-		if (sta->key)
-			ieee80211_key_free(sta->key);
-		else
+		if (sta->key) {
+			key = sta->key;
+			ieee80211_key_free(key);
+			WARN_ON(sta->key);
+		} else
 			ret = -ENOENT;
 
 		sta_info_put(sta);
@@ -185,7 +194,9 @@ static int ieee80211_del_key(struct wiphy *wiphy, struct net_device *dev,
 	if (!sdata->keys[key_idx])
 		return -ENOENT;
 
-	ieee80211_key_free(sdata->keys[key_idx]);
+	key = sdata->keys[key_idx];
+	ieee80211_key_free(key);
+	WARN_ON(sdata->keys[key_idx]);
 
 	return 0;
 }

net/mac80211/ieee80211_ioctl.c

@@ -33,8 +33,8 @@ static int ieee80211_set_encryption(struct net_device *dev, u8 *sta_addr,
 				    size_t key_len)
 {
 	struct ieee80211_local *local = wdev_priv(dev->ieee80211_ptr);
-	int ret = 0;
-	struct sta_info *sta;
+	int ret;
+	struct sta_info *sta = NULL;
 	struct ieee80211_key *key;
 	struct ieee80211_sub_if_data *sdata;
 
@@ -46,58 +46,64 @@ static int ieee80211_set_encryption(struct net_device *dev, u8 *sta_addr,
 		return -EINVAL;
 	}
 
-	if (is_broadcast_ether_addr(sta_addr)) {
-		sta = NULL;
-		key = sdata->keys[idx];
-	} else {
-		set_tx_key = 0;
-		/*
-		 * According to the standard, the key index of a pairwise
-		 * key must be zero. However, some AP are broken when it
-		 * comes to WEP key indices, so we work around this.
-		 */
-		if (idx != 0 && alg != ALG_WEP) {
-			printk(KERN_DEBUG "%s: set_encrypt - non-zero idx for "
-			       "individual key\n", dev->name);
-			return -EINVAL;
+	if (remove) {
+		if (is_broadcast_ether_addr(sta_addr)) {
+			key = sdata->keys[idx];
+		} else {
+			sta = sta_info_get(local, sta_addr);
+			if (!sta) {
+				ret = -ENOENT;
+				key = NULL;
+				goto err_out;
+			}
+
+			key = sta->key;
 		}
 
-		sta = sta_info_get(local, sta_addr);
-		if (!sta) {
-#ifdef CONFIG_MAC80211_VERBOSE_DEBUG
-			DECLARE_MAC_BUF(mac);
-			printk(KERN_DEBUG "%s: set_encrypt - unknown addr "
-			       "%s\n",
-			       dev->name, print_mac(mac, sta_addr));
-#endif /* CONFIG_MAC80211_VERBOSE_DEBUG */
+		if (!key)
+			ret = -ENOENT;
+		else
+			ret = 0;
+	} else {
+		key = ieee80211_key_alloc(alg, idx, key_len, _key);
+		if (!key)
+			return -ENOMEM;
+
+		if (!is_broadcast_ether_addr(sta_addr)) {
+			set_tx_key = 0;
+			/*
+			 * According to the standard, the key index of a
+			 * pairwise key must be zero. However, some AP are
+			 * broken when it comes to WEP key indices, so we
+			 * work around this.
+			 */
+			if (idx != 0 && alg != ALG_WEP) {
+				ret = -EINVAL;
+				goto err_out;
+			}
 
-			return -ENOENT;
+			sta = sta_info_get(local, sta_addr);
+			if (!sta) {
+				ret = -ENOENT;
+				goto err_out;
+			}
 		}
 
-		key = sta->key;
-	}
+		ieee80211_key_link(key, sdata, sta);
 
-	if (remove) {
-		ieee80211_key_free(key);
+		if (set_tx_key || (!sta && !sdata->default_key && key))
+			ieee80211_set_default_key(sdata, idx);
+
+		/* don't free key later */
 		key = NULL;
-	} else {
-		/*
-		 * Automatically frees any old key if present.
-		 */
-		key = ieee80211_key_alloc(sdata, sta, alg, idx, key_len, _key);
-		if (!key) {
-			ret = -ENOMEM;
-			goto err_out;
-		}
-	}
 
-	if (set_tx_key || (!sta && !sdata->default_key && key))
-		ieee80211_set_default_key(sdata, idx);
+		ret = 0;
+	}
 
-	ret = 0;
  err_out:
 	if (sta)
 		sta_info_put(sta);
+	ieee80211_key_free(key);
 	return ret;
 }
 

net/mac80211/ieee80211_key.h

@@ -13,6 +13,7 @@
 #include <linux/types.h>
 #include <linux/list.h>
 #include <linux/crypto.h>
+#include <linux/rcupdate.h>
 #include <net/mac80211.h>
 
 /* ALG_TKIP
@@ -45,7 +46,19 @@ struct ieee80211_local;
 struct ieee80211_sub_if_data;
 struct sta_info;
 
-#define KEY_FLAG_UPLOADED_TO_HARDWARE	(1<<0)
+/**
+ * enum ieee80211_internal_key_flags - internal key flags
+ *
+ * @KEY_FLAG_UPLOADED_TO_HARDWARE: Indicates that this key is present
+ *	in the hardware for TX crypto hardware acceleration.
+ * @KEY_FLAG_REMOVE_FROM_HARDWARE: Indicates to the key code that this
+ *	key is present in the hardware (but it cannot be used for
+ *	hardware acceleration any more!)
+ */
+enum ieee80211_internal_key_flags {
+	KEY_FLAG_UPLOADED_TO_HARDWARE	= BIT(0),
+	KEY_FLAG_REMOVE_FROM_HARDWARE	= BIT(1),
+};
 
 struct ieee80211_key {
 	struct ieee80211_local *local;
@@ -112,12 +125,17 @@ struct ieee80211_key {
 	struct ieee80211_key_conf conf;
 };
 
-struct ieee80211_key *ieee80211_key_alloc(struct ieee80211_sub_if_data *sdata,
-					  struct sta_info *sta,
-					  enum ieee80211_key_alg alg,
+struct ieee80211_key *ieee80211_key_alloc(enum ieee80211_key_alg alg,
 					  int idx,
 					  size_t key_len,
 					  const u8 *key_data);
+/*
+ * Insert a key into data structures (sdata, sta if necessary)
+ * to make it used, free old key.
+ */
+void ieee80211_key_link(struct ieee80211_key *key,
+			struct ieee80211_sub_if_data *sdata,
+			struct sta_info *sta);
 void ieee80211_key_free(struct ieee80211_key *key);
 void ieee80211_set_default_key(struct ieee80211_sub_if_data *sdata, int idx);
 void ieee80211_free_keys(struct ieee80211_sub_if_data *sdata);