bonding: fix store_arp_validate race with mode change

We need to protect store_arp_validate via rtnl because it can race with
mode changing and we can end up having arp_validate set in a mode
different from active-backup.
Signed-off-by: Nikolay Aleksandrov <nikolay@redhat.com>
Acked-by: Veaceslav Falico <vfalico@redhat.com>
Signed-off-by: David S. Miller <davem@davemloft.net>

drivers/net/bonding/bond_sysfs.c

@@ -419,27 +419,33 @@ static ssize_t bonding_store_arp_validate(struct device *d,
 					  struct device_attribute *attr,
 					  const char *buf, size_t count)
 {
-	int new_value;
+	int new_value, ret = count;
 	struct bonding *bond = to_bond(d);
 
+	if (!rtnl_trylock())
+		return restart_syscall();
 	new_value = bond_parse_parm(buf, arp_validate_tbl);
 	if (new_value < 0) {
 		pr_err("%s: Ignoring invalid arp_validate value %s\n",
 		       bond->dev->name, buf);
-		return -EINVAL;
+		ret = -EINVAL;
+		goto out;
 	}
 	if (new_value && (bond->params.mode != BOND_MODE_ACTIVEBACKUP)) {
 		pr_err("%s: arp_validate only supported in active-backup mode.\n",
 		       bond->dev->name);
-		return -EINVAL;
+		ret = -EINVAL;
+		goto out;
 	}
 	pr_info("%s: setting arp_validate to %s (%d).\n",
 		bond->dev->name, arp_validate_tbl[new_value].modename,
 		new_value);
 
 	bond->params.arp_validate = new_value;
+out:
+	rtnl_unlock();
 
-	return count;
+	return ret;
 }
 
 static DEVICE_ATTR(arp_validate, S_IRUGO | S_IWUSR, bonding_show_arp_validate,