bonding: fix multiple 3ad mode sysfs race conditions

When bond_3ad_get_active_agg_info() is used in all show_ad_ functions
it is not protected against slave manipulation and since it walks over
the slaves and uses them, this can easily result in NULL pointer
dereference or use of freed memory. Both the new wrapper and the
internal function are exported to the bonding as they're needed in
different places.

Signed-off-by: Nikolay Aleksandrov <[e-mail]>
Signed-off-by: David S. Miller <[e-mail]>

drivers/net/bonding/bond_3ad.c

···
 }
 
 /**
- * bond_3ad_get_active_agg_info - get information of the active aggregator
+ * __bond_3ad_get_active_agg_info - get information of the active aggregator
  * @bond: bonding struct to work on
  * @ad_info: ad_info struct to fill with the bond's info
  *
  * Returns:   0 on success
  *          < 0 on error
  */
-int bond_3ad_get_active_agg_info(struct bonding *bond, struct ad_info *ad_info)
+int __bond_3ad_get_active_agg_info(struct bonding *bond,
+				   struct ad_info *ad_info)
 {
 	struct aggregator *aggregator = NULL;
 	struct port *port;
···
 	return -1;
 }
 
+/* Wrapper used to hold bond->lock so no slave manipulation can occur */
+int bond_3ad_get_active_agg_info(struct bonding *bond, struct ad_info *ad_info)
+{
+	int ret;
+
+	read_lock(&bond->lock);
+	ret = __bond_3ad_get_active_agg_info(bond, ad_info);
+	read_unlock(&bond->lock);
+
+	return ret;
+}
+
 int bond_3ad_xmit_xor(struct sk_buff *skb, struct net_device *dev)
 {
 	struct slave *slave, *start_at;
···
 	struct ad_info ad_info;
 	int res = 1;
 
-	if (bond_3ad_get_active_agg_info(bond, &ad_info)) {
-		pr_debug("%s: Error: bond_3ad_get_active_agg_info failed\n",
+	if (__bond_3ad_get_active_agg_info(bond, &ad_info)) {
+		pr_debug("%s: Error: __bond_3ad_get_active_agg_info failed\n",
 			 dev->name);
 		goto out;
 	}

drivers/net/bonding/bond_3ad.h

···
 void bond_3ad_adapter_duplex_changed(struct slave *slave);
 void bond_3ad_handle_link_change(struct slave *slave, char link);
 int  bond_3ad_get_active_agg_info(struct bonding *bond, struct ad_info *ad_info);
+int  __bond_3ad_get_active_agg_info(struct bonding *bond,
+				    struct ad_info *ad_info);
 int bond_3ad_xmit_xor(struct sk_buff *skb, struct net_device *dev);
 int bond_3ad_lacpdu_recv(const struct sk_buff *skb, struct bonding *bond,
 			 struct slave *slave);

drivers/net/bonding/bond_procfs.c

···
 		seq_printf(seq, "Aggregator selection policy (ad_select): %s\n",
 			   ad_select_tbl[bond->params.ad_select].modename);
 
-		if (bond_3ad_get_active_agg_info(bond, &ad_info)) {
+		if (__bond_3ad_get_active_agg_info(bond, &ad_info)) {
 			seq_printf(seq, "bond %s has no active aggregator\n",
 				   bond->dev->name);
 		} else {

drivers/net/bonding/bond_sysfs.c

···
 }
 static DEVICE_ATTR(mii_status, S_IRUGO, bonding_show_mii_status, NULL);
 
-
 /*
  * Show current 802.3ad aggregator ID.
  */
···
 	if (bond->params.mode == BOND_MODE_8023AD) {
 		struct ad_info ad_info;
 		count = sprintf(buf, "%d\n",
-				(bond_3ad_get_active_agg_info(bond, &ad_info))
+				bond_3ad_get_active_agg_info(bond, &ad_info)
 				?  0 : ad_info.aggregator_id);
 	}
 
···
 	if (bond->params.mode == BOND_MODE_8023AD) {
 		struct ad_info ad_info;
 		count = sprintf(buf, "%d\n",
-				(bond_3ad_get_active_agg_info(bond, &ad_info))
+				bond_3ad_get_active_agg_info(bond, &ad_info)
 				?  0 : ad_info.ports);
 	}
 
···
 	if (bond->params.mode == BOND_MODE_8023AD) {
 		struct ad_info ad_info;
 		count = sprintf(buf, "%d\n",
-				(bond_3ad_get_active_agg_info(bond, &ad_info))
+				bond_3ad_get_active_agg_info(bond, &ad_info)
 				?  0 : ad_info.actor_key);
 	}
 
···
 	if (bond->params.mode == BOND_MODE_8023AD) {
 		struct ad_info ad_info;
 		count = sprintf(buf, "%d\n",
-				(bond_3ad_get_active_agg_info(bond, &ad_info))
+				bond_3ad_get_active_agg_info(bond, &ad_info)
 				?  0 : ad_info.partner_key);
 	}