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>

5 files changed, 203 insertions, 98 deletions

diff --git a/net/mac80211/cfg.c b/net/mac80211/cfg.c
index b0c41a0cee79..e7535ffc8e1c 100644
--- a/net/mac80211/cfg.c
+++ b/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;
 }
diff --git a/net/mac80211/ieee80211_ioctl.c b/net/mac80211/ieee80211_ioctl.c
index 54ad07aafe2d..7551db3f3abc 100644
--- a/net/mac80211/ieee80211_ioctl.c
+++ b/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;
 }
 
diff --git a/net/mac80211/ieee80211_key.h b/net/mac80211/ieee80211_key.h
index fc770e98d47b..d670e6dbfa39 100644
--- a/net/mac80211/ieee80211_key.h
+++ b/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);
diff --git a/net/mac80211/key.c b/net/mac80211/key.c
index ed57fb8e82fc..60aaaf471544 100644
--- a/net/mac80211/key.c
+++ b/net/mac80211/key.c
@@ -13,6 +13,7 @@
 #include <linux/etherdevice.h>
 #include <linux/list.h>
 #include <linux/rcupdate.h>
+#include <linux/rtnetlink.h>
 #include <net/mac80211.h>
 #include "ieee80211_i.h"
 #include "debugfs_key.h"
@@ -34,6 +35,10 @@
  *
  * All operations here are called under RTNL so no extra locking is
  * required.
+ *
+ * NOTE: This code requires that sta info *destruction* is done under
+ *       RTNL, otherwise it can try to access already freed STA structs
+ *       when a STA key is being freed.
  */
 
 static const u8 bcast_addr[ETH_ALEN] = { 0xFF, 0xFF, 0xFF, 0xFF, 0xFF, 0xFF };
@@ -84,16 +89,25 @@ static void ieee80211_key_enable_hw_accel(struct ieee80211_key *key)
                        key->conf.keyidx, print_mac(mac, addr), ret);
 }
 
+static void ieee80211_key_mark_hw_accel_off(struct ieee80211_key *key)
+{
+        if (key->flags & KEY_FLAG_UPLOADED_TO_HARDWARE) {
+                key->flags &= ~KEY_FLAG_UPLOADED_TO_HARDWARE;
+                key->flags |= KEY_FLAG_REMOVE_FROM_HARDWARE;
+        }
+}
+
 static void ieee80211_key_disable_hw_accel(struct ieee80211_key *key)
 {
         const u8 *addr;
         int ret;
         DECLARE_MAC_BUF(mac);
 
-        if (!key->local->ops->set_key)
+        if (!key || !key->local->ops->set_key)
                 return;
 
-        if (!(key->flags & KEY_FLAG_UPLOADED_TO_HARDWARE))
+        if (!(key->flags & KEY_FLAG_UPLOADED_TO_HARDWARE) &&
+            !(key->flags & KEY_FLAG_REMOVE_FROM_HARDWARE))
                 return;
 
         addr = get_mac_for_key(key);
@@ -108,12 +122,11 @@ static void ieee80211_key_disable_hw_accel(struct ieee80211_key *key)
                        wiphy_name(key->local->hw.wiphy),
                        key->conf.keyidx, print_mac(mac, addr), ret);
 
-        key->flags &= ~KEY_FLAG_UPLOADED_TO_HARDWARE;
+        key->flags &= ~(KEY_FLAG_UPLOADED_TO_HARDWARE |
+                        KEY_FLAG_REMOVE_FROM_HARDWARE);
 }
 
-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)
@@ -138,10 +151,6 @@ struct ieee80211_key *ieee80211_key_alloc(struct ieee80211_sub_if_data *sdata,
         key->conf.keylen = key_len;
         memcpy(key->conf.key, key_data, key_len);
 
-        key->local = sdata->local;
-        key->sdata = sdata;
-        key->sta = sta;
-
         if (alg == ALG_CCMP) {
                 /*
                  * Initialize AES key state here as an optimization so that
@@ -154,13 +163,62 @@ struct ieee80211_key *ieee80211_key_alloc(struct ieee80211_sub_if_data *sdata,
                 }
         }
 
-        ieee80211_debugfs_key_add(key->local, key);
+        return key;
+}
 
-        /* remove key first */
-        if (sta)
-                ieee80211_key_free(sta->key);
-        else
-                ieee80211_key_free(sdata->keys[idx]);
+static void __ieee80211_key_replace(struct ieee80211_sub_if_data *sdata,
+                                    struct sta_info *sta,
+                                    struct ieee80211_key *key,
+                                    struct ieee80211_key *new)
+{
+        int idx, defkey;
+
+        if (sta) {
+                rcu_assign_pointer(sta->key, new);
+        } else {
+                WARN_ON(new && key && new->conf.keyidx != key->conf.keyidx);
+
+                if (key)
+                        idx = key->conf.keyidx;
+                else
+                        idx = new->conf.keyidx;
+
+                defkey = key && sdata->default_key == key;
+
+                if (defkey && !new)
+                        ieee80211_set_default_key(sdata, -1);
+
+                rcu_assign_pointer(sdata->keys[idx], new);
+
+                if (defkey && new)
+                        ieee80211_set_default_key(sdata, new->conf.keyidx);
+        }
+
+        if (key) {
+                ieee80211_key_mark_hw_accel_off(key);
+                list_del(&key->list);
+        }
+}
+
+void ieee80211_key_link(struct ieee80211_key *key,
+                        struct ieee80211_sub_if_data *sdata,
+                        struct sta_info *sta)
+{
+        struct ieee80211_key *old_key;
+        int idx;
+
+        ASSERT_RTNL();
+        might_sleep();
+
+        BUG_ON(!sdata);
+        BUG_ON(!key);
+
+        idx = key->conf.keyidx;
+        key->local = sdata->local;
+        key->sdata = sdata;
+        key->sta = sta;
+
+        ieee80211_debugfs_key_add(key->local, key);
 
         if (sta) {
                 ieee80211_debugfs_key_sta_link(key, sta);
@@ -186,50 +244,53 @@ struct ieee80211_key *ieee80211_key_alloc(struct ieee80211_sub_if_data *sdata,
                 }
         }
 
-        /* enable hwaccel if appropriate */
-        if (netif_running(key->sdata->dev))
-                ieee80211_key_enable_hw_accel(key);
-
         if (sta)
-                rcu_assign_pointer(sta->key, key);
+                old_key = sta->key;
         else
-                rcu_assign_pointer(sdata->keys[idx], key);
+                old_key = sdata->keys[idx];
+
+        __ieee80211_key_replace(sdata, sta, old_key, key);
 
         list_add(&key->list, &sdata->key_list);
 
-        return key;
+        synchronize_rcu();
+
+        ieee80211_key_free(old_key);
+        ieee80211_key_enable_hw_accel(key);
 }
 
 void ieee80211_key_free(struct ieee80211_key *key)
 {
+        ASSERT_RTNL();
+        might_sleep();
+
         if (!key)
                 return;
 
-        if (key->sta) {
-                rcu_assign_pointer(key->sta->key, NULL);
-        } else {
-                if (key->sdata->default_key == key)
-                        ieee80211_set_default_key(key->sdata, -1);
-                if (key->conf.keyidx >= 0 &&
-                    key->conf.keyidx < NUM_DEFAULT_KEYS)
-                        rcu_assign_pointer(key->sdata->keys[key->conf.keyidx],
-                                           NULL);
-                else
-                        WARN_ON(1);
-        }
+        if (key->sdata) {
+                /*
+                 * Replace key with nothingness.
+                 *
+                 * Because other code may have key reference (RCU protected)
+                 * right now, we then wait for a grace period before freeing
+                 * it.
+                 */
+                __ieee80211_key_replace(key->sdata, key->sta, key, NULL);
 
-        /* wait for all key users to complete */
-        synchronize_rcu();
+                synchronize_rcu();
 
-        /* remove from hwaccel if appropriate */
-        ieee80211_key_disable_hw_accel(key);
+                /*
+                 * Remove from hwaccel if appropriate, this will
+                 * only happen when the key is actually unlinked,
+                 * it will already be done when the key was replaced.
+                 */
+                ieee80211_key_disable_hw_accel(key);
+        }
 
         if (key->conf.alg == ALG_CCMP)
                 ieee80211_aes_key_free(key->u.ccmp.tfm);
         ieee80211_debugfs_key_remove(key);
 
-        list_del(&key->list);
-
         kfree(key);
 }
 
@@ -253,6 +314,10 @@ void ieee80211_set_default_key(struct ieee80211_sub_if_data *sdata, int idx)
 void ieee80211_free_keys(struct ieee80211_sub_if_data *sdata)
 {
         struct ieee80211_key *key, *tmp;
+        LIST_HEAD(tmp_list);
+
+        ASSERT_RTNL();
+        might_sleep();
 
         list_for_each_entry_safe(key, tmp, &sdata->key_list, list)
                 ieee80211_key_free(key);
@@ -262,8 +327,10 @@ void ieee80211_enable_keys(struct ieee80211_sub_if_data *sdata)
 {
         struct ieee80211_key *key;
 
-        WARN_ON(!netif_running(sdata->dev));
-        if (!netif_running(sdata->dev))
+        ASSERT_RTNL();
+        might_sleep();
+
+        if (WARN_ON(!netif_running(sdata->dev)))
                 return;
 
         list_for_each_entry(key, &sdata->key_list, list)
@@ -274,6 +341,9 @@ void ieee80211_disable_keys(struct ieee80211_sub_if_data *sdata)
 {
         struct ieee80211_key *key;
 
+        ASSERT_RTNL();
+        might_sleep();
+
         list_for_each_entry(key, &sdata->key_list, list)
                 ieee80211_key_disable_hw_accel(key);
 }
diff --git a/net/mac80211/sta_info.c b/net/mac80211/sta_info.c
index c6c0df4bbd2c..e384e6632d97 100644
--- a/net/mac80211/sta_info.c
+++ b/net/mac80211/sta_info.c
@@ -312,7 +312,7 @@ void sta_info_free(struct sta_info *sta)
 #endif /* CONFIG_MAC80211_VERBOSE_DEBUG */
 
         ieee80211_key_free(sta->key);
-        sta->key = NULL;
+        WARN_ON(sta->key);
 
         if (local->ops->sta_notify) {
                 struct ieee80211_sub_if_data *sdata;