batman-adv: Fix reference counting of vlan object for tt_local_entry

commit a33d970d upstream.

The batadv_tt_local_entry was specific to a batadv_softif_vlan and held an
implicit reference to it. But this reference was never stored in form of a
pointer in the tt_local_entry itself. Instead batadv_tt_local_remove,
batadv_tt_local_table_free and batadv_tt_local_purge_pending_clients depend
on a consistent state of bat_priv->softif_vlan_list and that
batadv_softif_vlan_get always returns the batadv_softif_vlan object which
it has a reference for. But batadv_softif_vlan_get cannot guarantee that
because it is working only with rcu_read_lock on this list. It can
therefore happen that an vid is in this list twice or that
batadv_softif_vlan_get cannot find the batadv_softif_vlan for an vid due to
some other list operations taking place at the same time.

Instead add a batadv_softif_vlan pointer directly in batadv_tt_local_entry
which will be used for the reference counter decremented on release of
batadv_tt_local_entry.

Fixes: 35df3b29 ("batman-adv: fix TT VLAN inconsistency on VLAN re-add")
Signed-off-by: Sven Eckelmann <sven@narfation.org>
Acked-by: Antonio Quartulli <a@unstable.cc>
Signed-off-by: Marek Lindner <mareklindner@neomailbox.ch>
Signed-off-by: Antonio Quartulli <a@unstable.cc>
[bwh: Backported to 3.16:
 - s/_put/_free_ref/ in various function names
 - Adjust context]
Signed-off-by: Ben Hutchings <ben@decadent.org.uk>

net/batman-adv/translation-table.c

@@ -176,8 +176,10 @@ batadv_tt_global_hash_find(struct batadv_priv *bat_priv, const uint8_t *addr,
 static void
 batadv_tt_local_entry_free_ref(struct batadv_tt_local_entry *tt_local_entry)
 {
-	if (atomic_dec_and_test(&tt_local_entry->common.refcount))
+	if (atomic_dec_and_test(&tt_local_entry->common.refcount)) {
+		batadv_softif_vlan_free_ref(tt_local_entry->vlan);
 		kfree_rcu(tt_local_entry, common.rcu);
+	}
 }
 
 /**
@@ -595,6 +597,7 @@ bool batadv_tt_local_add(struct net_device *soft_iface, const uint8_t *addr,
 	atomic_set(&tt_local->common.refcount, 2);
 	tt_local->last_seen = jiffies;
 	tt_local->common.added_at = tt_local->last_seen;
+	tt_local->vlan = vlan;
 
 	/* the batman interface mac and multicast addresses should never be
 	 * purged
@@ -908,7 +911,6 @@ int batadv_tt_local_seq_print_text(struct seq_file *seq, void *offset)
 	struct batadv_tt_common_entry *tt_common_entry;
 	struct batadv_tt_local_entry *tt_local;
 	struct batadv_hard_iface *primary_if;
-	struct batadv_softif_vlan *vlan;
 	struct hlist_head *head;
 	unsigned short vid;
 	uint32_t i;
@@ -944,14 +946,6 @@ int batadv_tt_local_seq_print_text(struct seq_file *seq, void *offset)
 			last_seen_msecs = last_seen_msecs % 1000;
 
 			no_purge = tt_common_entry->flags & np_flag;
-
-			vlan = batadv_softif_vlan_get(bat_priv, vid);
-			if (!vlan) {
-				seq_printf(seq, "Cannot retrieve VLAN %d\n",
-					   BATADV_PRINT_VID(vid));
-				continue;
-			}
-
 			seq_printf(seq,
 				   " * %pM %4i [%c%c%c%c%c%c] %3u.%03u   (%#.8x)\n",
 				   tt_common_entry->addr,
@@ -969,9 +963,7 @@ int batadv_tt_local_seq_print_text(struct seq_file *seq, void *offset)
 				    BATADV_TT_CLIENT_ISOLA ? 'I' : '.'),
 				   no_purge ? 0 : last_seen_secs,
 				   no_purge ? 0 : last_seen_msecs,
-				   vlan->tt.crc);
-
-			batadv_softif_vlan_free_ref(vlan);
+				   tt_local->vlan->tt.crc);
 		}
 		rcu_read_unlock();
 	}
@@ -1016,7 +1008,6 @@ uint16_t batadv_tt_local_remove(struct batadv_priv *bat_priv,
 {
 	struct batadv_tt_local_entry *tt_local_entry;
 	uint16_t flags, curr_flags = BATADV_NO_FLAGS;
-	struct batadv_softif_vlan *vlan;
 	void *tt_entry_exists;
 
 	tt_local_entry = batadv_tt_local_hash_find(bat_priv, addr, vid);
@@ -1056,14 +1047,6 @@ uint16_t batadv_tt_local_remove(struct batadv_priv *bat_priv,
 	/* extra call to free the local tt entry */
 	batadv_tt_local_entry_free_ref(tt_local_entry);
 
-	/* decrease the reference held for this vlan */
-	vlan = batadv_softif_vlan_get(bat_priv, vid);
-	if (!vlan)
-		goto out;
-
-	batadv_softif_vlan_free_ref(vlan);
-	batadv_softif_vlan_free_ref(vlan);
-
 out:
 	if (tt_local_entry)
 		batadv_tt_local_entry_free_ref(tt_local_entry);
@@ -1136,7 +1119,6 @@ static void batadv_tt_local_table_free(struct batadv_priv *bat_priv)
 	spinlock_t *list_lock; /* protects write access to the hash lists */
 	struct batadv_tt_common_entry *tt_common_entry;
 	struct batadv_tt_local_entry *tt_local;
-	struct batadv_softif_vlan *vlan;
 	struct hlist_node *node_tmp;
 	struct hlist_head *head;
 	uint32_t i;
@@ -1158,14 +1140,6 @@ static void batadv_tt_local_table_free(struct batadv_priv *bat_priv)
 						struct batadv_tt_local_entry,
 						common);
 
-			/* decrease the reference held for this vlan */
-			vlan = batadv_softif_vlan_get(bat_priv,
-						      tt_common_entry->vid);
-			if (vlan) {
-				batadv_softif_vlan_free_ref(vlan);
-				batadv_softif_vlan_free_ref(vlan);
-			}
-
 			batadv_tt_local_entry_free_ref(tt_local);
 		}
 		spin_unlock_bh(list_lock);
@@ -3174,7 +3148,6 @@ static void batadv_tt_local_purge_pending_clients(struct batadv_priv *bat_priv)
 	struct batadv_hashtable *hash = bat_priv->tt.local_hash;
 	struct batadv_tt_common_entry *tt_common;
 	struct batadv_tt_local_entry *tt_local;
-	struct batadv_softif_vlan *vlan;
 	struct hlist_node *node_tmp;
 	struct hlist_head *head;
 	spinlock_t *list_lock; /* protects write access to the hash lists */
@@ -3204,13 +3177,6 @@ static void batadv_tt_local_purge_pending_clients(struct batadv_priv *bat_priv)
 						struct batadv_tt_local_entry,
 						common);
 
-			/* decrease the reference held for this vlan */
-			vlan = batadv_softif_vlan_get(bat_priv, tt_common->vid);
-			if (vlan) {
-				batadv_softif_vlan_free_ref(vlan);
-				batadv_softif_vlan_free_ref(vlan);
-			}
-
 			batadv_tt_local_entry_free_ref(tt_local);
 		}
 		spin_unlock_bh(list_lock);

net/batman-adv/types.h

@@ -934,10 +934,12 @@ struct batadv_tt_common_entry {
  * struct batadv_tt_local_entry - translation table local entry data
  * @common: general translation table data
  * @last_seen: timestamp used for purging stale tt local entries
+ * @vlan: soft-interface vlan of the entry
  */
 struct batadv_tt_local_entry {
 	struct batadv_tt_common_entry common;
 	unsigned long last_seen;
+	struct batadv_softif_vlan *vlan;
 };
 
 /**