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>

1 files changed, 113 insertions, 43 deletions

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);
 }