batman-adv: Make bat_priv->curr_gw an rcu protected pointer

The rcu protected macros rcu_dereference() and rcu_assign_pointer()
for the bat_priv->curr_gw need to be used, as well as spin/rcu locking.

Otherwise we might end up using a curr_gw pointer pointing to already
freed memory.

Reported-by: Sven Eckelmann <sven@narfation.org>
Signed-off-by: Linus Lüssing <linus.luessing@ascom.ch>
Signed-off-by: Marek Lindner <lindner_marek@yahoo.de>

2 files changed, 72 insertions, 32 deletions

diff --git a/net/batman-adv/gateway_client.c b/net/batman-adv/gateway_client.c
index 517e001605d9..a3e842fd0f9c 100644
--- a/net/batman-adv/gateway_client.c
+++ b/net/batman-adv/gateway_client.c
@@ -44,19 +44,29 @@ static void gw_node_free_ref(struct gw_node *gw_node)
 
 void *gw_get_selected(struct bat_priv *bat_priv)
 {
-        struct gw_node *curr_gateway_tmp = bat_priv->curr_gw;
+        struct gw_node *curr_gateway_tmp;
+        struct orig_node *orig_node = NULL;
 
+        rcu_read_lock();
+        curr_gateway_tmp = rcu_dereference(bat_priv->curr_gw);
         if (!curr_gateway_tmp)
-                return NULL;
+                goto out;
+
+        orig_node = curr_gateway_tmp->orig_node;
 
-        return curr_gateway_tmp->orig_node;
+out:
+        rcu_read_unlock();
+        return orig_node;
 }
 
 void gw_deselect(struct bat_priv *bat_priv)
 {
-        struct gw_node *gw_node = bat_priv->curr_gw;
+        struct gw_node *gw_node;
 
-        bat_priv->curr_gw = NULL;
+        spin_lock_bh(&bat_priv->gw_list_lock);
+        gw_node = rcu_dereference(bat_priv->curr_gw);
+        rcu_assign_pointer(bat_priv->curr_gw, NULL);
+        spin_unlock_bh(&bat_priv->gw_list_lock);
 
         if (gw_node)
                 gw_node_free_ref(gw_node);
@@ -64,12 +74,15 @@ void gw_deselect(struct bat_priv *bat_priv)
 
 static void gw_select(struct bat_priv *bat_priv, struct gw_node *new_gw_node)
 {
-        struct gw_node *curr_gw_node = bat_priv->curr_gw;
+        struct gw_node *curr_gw_node;
 
         if (new_gw_node && !atomic_inc_not_zero(&new_gw_node->refcount))
                 new_gw_node = NULL;
 
-        bat_priv->curr_gw = new_gw_node;
+        spin_lock_bh(&bat_priv->gw_list_lock);
+        curr_gw_node = rcu_dereference(bat_priv->curr_gw);
+        rcu_assign_pointer(bat_priv->curr_gw, new_gw_node);
+        spin_unlock_bh(&bat_priv->gw_list_lock);
 
         if (curr_gw_node)
                 gw_node_free_ref(curr_gw_node);
@@ -78,7 +91,7 @@ static void gw_select(struct bat_priv *bat_priv, struct gw_node *new_gw_node)
 void gw_election(struct bat_priv *bat_priv)
 {
         struct hlist_node *node;
-        struct gw_node *gw_node, *curr_gw_tmp = NULL;
+        struct gw_node *gw_node, *curr_gw, *curr_gw_tmp = NULL;
         uint8_t max_tq = 0;
         uint32_t max_gw_factor = 0, tmp_gw_factor = 0;
         int down, up;
@@ -92,19 +105,23 @@ void gw_election(struct bat_priv *bat_priv)
         if (atomic_read(&bat_priv->gw_mode) != GW_MODE_CLIENT)
                 return;
 
-        if (bat_priv->curr_gw)
+        rcu_read_lock();
+        curr_gw = rcu_dereference(bat_priv->curr_gw);
+        if (curr_gw) {
+                rcu_read_unlock();
                 return;
+        }
 
-        rcu_read_lock();
         if (hlist_empty(&bat_priv->gw_list)) {
-                rcu_read_unlock();
 
-                if (bat_priv->curr_gw) {
+                if (curr_gw) {
+                        rcu_read_unlock();
                         bat_dbg(DBG_BATMAN, bat_priv,
                                 "Removing selected gateway - "
                                 "no gateway in range\n");
                         gw_deselect(bat_priv);
-                }
+                } else
+                        rcu_read_unlock();
 
                 return;
         }
@@ -153,12 +170,12 @@ void gw_election(struct bat_priv *bat_priv)
                         max_gw_factor = tmp_gw_factor;
         }
 
-        if (bat_priv->curr_gw != curr_gw_tmp) {
-                if ((bat_priv->curr_gw) && (!curr_gw_tmp))
+        if (curr_gw != curr_gw_tmp) {
+                if ((curr_gw) && (!curr_gw_tmp))
                         bat_dbg(DBG_BATMAN, bat_priv,
                                 "Removing selected gateway - "
                                 "no gateway in range\n");
-                else if ((!bat_priv->curr_gw) && (curr_gw_tmp))
+                else if ((!curr_gw) && (curr_gw_tmp))
                         bat_dbg(DBG_BATMAN, bat_priv,
                                 "Adding route to gateway %pM "
                                 "(gw_flags: %i, tq: %i)\n",
@@ -181,31 +198,35 @@ void gw_election(struct bat_priv *bat_priv)
 
 void gw_check_election(struct bat_priv *bat_priv, struct orig_node *orig_node)
 {
-        struct gw_node *curr_gateway_tmp = bat_priv->curr_gw;
+        struct gw_node *curr_gateway_tmp;
         uint8_t gw_tq_avg, orig_tq_avg;
 
+        rcu_read_lock();
+        curr_gateway_tmp = rcu_dereference(bat_priv->curr_gw);
         if (!curr_gateway_tmp)
-                return;
+                goto out_rcu;
 
         if (!curr_gateway_tmp->orig_node)
-                goto deselect;
+                goto deselect_rcu;
 
         if (!curr_gateway_tmp->orig_node->router)
-                goto deselect;
+                goto deselect_rcu;
 
         /* this node already is the gateway */
         if (curr_gateway_tmp->orig_node == orig_node)
-                return;
+                goto out_rcu;
 
         if (!orig_node->router)
-                return;
+                goto out_rcu;
 
         gw_tq_avg = curr_gateway_tmp->orig_node->router->tq_avg;
+        rcu_read_unlock();
+
         orig_tq_avg = orig_node->router->tq_avg;
 
         /* the TQ value has to be better */
         if (orig_tq_avg < gw_tq_avg)
-                return;
+                goto out;
 
         /**
          * if the routing class is greater than 3 the value tells us how much
@@ -213,15 +234,23 @@ void gw_check_election(struct bat_priv *bat_priv, struct orig_node *orig_node)
          **/
         if ((atomic_read(&bat_priv->gw_sel_class) > 3) &&
             (orig_tq_avg - gw_tq_avg < atomic_read(&bat_priv->gw_sel_class)))
-                return;
+                goto out;
 
         bat_dbg(DBG_BATMAN, bat_priv,
                 "Restarting gateway selection: better gateway found (tq curr: "
                 "%i, tq new: %i)\n",
                 gw_tq_avg, orig_tq_avg);
+        goto deselect;
 
+out_rcu:
+        rcu_read_unlock();
+        goto out;
+deselect_rcu:
+        rcu_read_unlock();
 deselect:
         gw_deselect(bat_priv);
+out:
+        return;
 }
 
 static void gw_node_add(struct bat_priv *bat_priv,
@@ -278,7 +307,7 @@ void gw_node_update(struct bat_priv *bat_priv,
                                 "Gateway %pM removed from gateway list\n",
                                 orig_node->orig);
 
-                        if (gw_node == bat_priv->curr_gw) {
+                        if (gw_node == rcu_dereference(bat_priv->curr_gw)) {
                                 rcu_read_unlock();
                                 gw_deselect(bat_priv);
                                 return;
@@ -316,7 +345,7 @@ void gw_node_purge(struct bat_priv *bat_priv)
                     atomic_read(&bat_priv->mesh_state) == MESH_ACTIVE)
                         continue;
 
-                if (bat_priv->curr_gw == gw_node)
+                if (rcu_dereference(bat_priv->curr_gw) == gw_node)
                         gw_deselect(bat_priv);
 
                 hlist_del_rcu(&gw_node->list);
@@ -330,12 +359,16 @@ void gw_node_purge(struct bat_priv *bat_priv)
 static int _write_buffer_text(struct bat_priv *bat_priv,
                               struct seq_file *seq, struct gw_node *gw_node)
 {
-        int down, up;
+        struct gw_node *curr_gw;
+        int down, up, ret;
 
         gw_bandwidth_to_kbit(gw_node->orig_node->gw_flags, &down, &up);
 
-        return seq_printf(seq, "%s %pM (%3i) %pM [%10s]: %3i - %i%s/%i%s\n",
-                       (bat_priv->curr_gw == gw_node ? "=>" : "  "),
+        rcu_read_lock();
+        curr_gw = rcu_dereference(bat_priv->curr_gw);
+
+        ret = seq_printf(seq, "%s %pM (%3i) %pM [%10s]: %3i - %i%s/%i%s\n",
+                       (curr_gw == gw_node ? "=>" : "  "),
                        gw_node->orig_node->orig,
                        gw_node->orig_node->router->tq_avg,
                        gw_node->orig_node->router->addr,
@@ -345,6 +378,9 @@ static int _write_buffer_text(struct bat_priv *bat_priv,
                        (down > 2048 ? "MBit" : "KBit"),
                        (up > 2048 ? up / 1024 : up),
                        (up > 2048 ? "MBit" : "KBit"));
+
+        rcu_read_unlock();
+        return ret;
 }
 
 int gw_client_seq_print_text(struct seq_file *seq, void *offset)
@@ -465,8 +501,12 @@ int gw_is_target(struct bat_priv *bat_priv, struct sk_buff *skb)
         if (atomic_read(&bat_priv->gw_mode) == GW_MODE_SERVER)
                 return -1;
 
-        if (!bat_priv->curr_gw)
+        rcu_read_lock();
+        if (!rcu_dereference(bat_priv->curr_gw)) {
+                rcu_read_unlock();
                 return 0;
+        }
+        rcu_read_unlock();
 
         return 1;
 }
diff --git a/net/batman-adv/types.h b/net/batman-adv/types.h
index e1f3e5e71555..3dd5e77a0aa0 100644
--- a/net/batman-adv/types.h
+++ b/net/batman-adv/types.h
@@ -162,7 +162,7 @@ struct bat_priv {
         spinlock_t forw_bcast_list_lock; /* protects  */
         spinlock_t hna_lhash_lock; /* protects hna_local_hash */
         spinlock_t hna_ghash_lock; /* protects hna_global_hash */
-        spinlock_t gw_list_lock; /* protects gw_list */
+        spinlock_t gw_list_lock; /* protects gw_list and curr_gw */
         spinlock_t vis_hash_lock; /* protects vis_hash */
         spinlock_t vis_list_lock; /* protects vis_info::recv_list */
         spinlock_t softif_neigh_lock; /* protects soft-interface neigh list */
@@ -171,7 +171,7 @@ struct bat_priv {
         struct delayed_work hna_work;
         struct delayed_work orig_work;
         struct delayed_work vis_work;
-        struct gw_node *curr_gw;
+        struct gw_node __rcu *curr_gw;  /* rcu protected pointer */
         struct vis_info *my_vis_info;
 };